Download 313 ALGOLOY DERS NOTLARI

313 ALGOLOY
DERS NOTLARI
Doç. Dr. Muzaffer Dügel
AİBÜ Fen-Edebiyat Fakültesi Biyoloji Bölümü
İÇİNDEKİLER
1
INTRODUCTION TO THE ALGAE ................................................................................. 1
1.1
2
3
4
Classification ............................................................................................................... 1
MORPHOLOGY ................................................................................................................ 3
2.1
Biochemical and structural features of Algae.............................................................. 3
2.2
Range of Morphological Diversity in Algae ............................................................... 4
2.2.1
Unicellular organization ....................................................................................... 4
2.2.2
Colonial Organization .......................................................................................... 5
2.2.3
Filamentous organization ..................................................................................... 6
2.2.4
Siphonaceous organization ................................................................................... 7
2.2.5
Parenchymatous organization .............................................................................. 8
REPRODUCTION AND LIFE HISTORY........................................................................ 9
3.1
Asexual reproduction of algae ..................................................................................... 9
3.2
Sexual reproduction of algae ..................................................................................... 11
CYTOLOGY OF ALGAE ............................................................................................... 14
4.1
Cell walls ................................................................................................................... 14
4.1.1
5
Coccoliths: .......................................................................................................... 14
4.2
Flagella ...................................................................................................................... 15
4.3
Plastids (chromatophore = chloroplast) ..................................................................... 17
4.4
Algal pigments ........................................................................................................... 17
4.4.1
Chlorophyll pigments ......................................................................................... 17
4.4.2
Carotenoid pigments .......................................................................................... 19
4.4.3
Phycobilin pigments ........................................................................................... 19
4.4.4
Chromatic adaptation ......................................................................................... 20
4.4.5
Endosymbiosis and origin of plastids................................................................. 21
4.5
Pyrenoids ................................................................................................................... 23
4.6
Mitochondria ............................................................................................................. 23
4.7
Eyespots (stigma) ...................................................................................................... 23
4.8
Golgi apparatus .......................................................................................................... 24
DIVERSITY OF THE ALGAE ....................................................................................... 25
5.1
Algae in the marine habitat ........................................................................................ 25
5.2
The Algae of Freshwater ........................................................................................... 27
5.3
Algal blooms.............................................................................................................. 28
5.4
Terrestrial algae ......................................................................................................... 28
5.5
Human uses of algae .................................................................................................. 29
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6
5.6
Variations in algal nutrition ....................................................................................... 29
5.7
Summaries of the nine algal phyla ............................................................................ 30
GENERAL FEATURES OF ALGAL DIVISIONS ........................................................ 33
6.1
Division CYANOBACTERIA (Blue-green algae) ................................................... 33
6.1.1
Habitat ................................................................................................................ 34
6.1.2
Nitrogen Fixation ............................................................................................... 34
6.1.3
Protoplast ............................................................................................................ 34
6.1.4
Motility ............................................................................................................... 35
6.1.5
Form ................................................................................................................... 35
6.1.6
Reproduction ...................................................................................................... 35
6.1.7
Akinetes .............................................................................................................. 36
6.1.8
Cyanobacteria and the origin of an oxygen-rich atmosphere ............................. 37
6.2
Division EUGLENOPHYTA .................................................................................... 38
6.2.1
Reproduction ...................................................................................................... 39
6.2.2
Euglenoid ecology .............................................................................................. 40
6.3
Division CRYPTOPHYTA ....................................................................................... 40
6.3.1
6.4
Division HAPTOPHYTA .......................................................................................... 42
6.4.1
Fossil record ....................................................................................................... 43
6.4.2
Thallus type ........................................................................................................ 44
6.5
Division DINOPHYTA (dinoflagellates) .................................................................. 45
6.5.1
6.6
6.7
Bioluminescence ................................................................................................ 46
Division OCHROPHYTA ......................................................................................... 47
6.6.1
7
Ecology............................................................................................................... 41
Diatoms .............................................................................................................. 48
Division CHLOROPHYTA ....................................................................................... 48
6.7.1
Class: Charophycea ............................................................................................ 49
6.7.2
Order: Charales .................................................................................................. 49
6.7.3
Killer algae in the Mediterranean Sea ................................................................ 50
ECONOMIC ASPECTS .................................................................................................. 51
7.1
Agar ........................................................................................................................... 51
7.2
Alginic acid (alginate) ............................................................................................... 52
7.3
Diatomite ................................................................................................................... 52
7.4
Other aspect of using algae ........................................................................................ 53
7.4.1
Fertilizer ............................................................................................................. 53
7.4.2
Fodder................................................................................................................. 53
7.4.3
8
Food .................................................................................................................... 53
BIOLOGICAL ASSESSMENT IN WATER POLLUTION. .......................................... 54
iii
1
INTRODUCTION TO THE ALGAE
From tiny single-celled species one micrometer in diameter to giant seaweeds over 50 meters
long, algae (sing., alga) are abundant and ancient organisms that can be found in virtually
every ecosystem in the biosphere. (The word alga is derived from Latin word for “seaweed”).
For billions of years algae have exerted profound effects on our planet and its biota, and they
continue to do so today. People from many cultures, ancient and modern, have used algae for
a variety of purposes.
Although most algae are autotrophic, they are not considered plants because they lack many
plant structures, such as roots, stems, and leaves. Algae lack a cuticle, which is a waxy
covering over the aerial parts of plants that reduce water loss. When actively growing, algae
are restricted to damp or wet environments such as the ocean; freshwater ponds, lakes, and
streams; hot spring; polar ice; alpine snow; moist soil, threes, and rocks; and the bodies of
certain animals, including sloths, sea anemones, corals, and worms. Also most algae do not
have multicellular gametangia (sing. gametangium; reproductive structure in which gametes
are produced). Algal gametangia generally are formed from single cells.
1.1
Classification
The history of taxonomy at the kingdom level is a good example of the process of science.
From the time of Aristotle to the mid 19th century, biologist divided organisms into two
kingdoms: Plantae and Animalia. After the development of microscopes, it became
increasingly obvious that many organisms could not be easily assigned to either the plant or
the animal kingdom. For example, the unicellular organism Euglena, which has been
classified at various times in the plant kingdom and in the animal kingdom, carries on
photosynthesis in the light but in the dark uses its flagellum to move about in search of food.
In 1886 a German biologist Ernst Haeckel, proposed that a third kingdom, Protista, be
established to accommodate bacteria and other microorganisms such as Euglena. That did not
appear to fit into the plant or animal kingdoms. Today many biologists place algae (including
multicellular forms), protozoa, water molds, and slime molds in kingdom Protista.
Table 1.1 Two super kingdoms and six kingdoms
Superkingdom
Kingdom
Characteristics
Prokaryota
Eubacteria
Lack distinct nuclei and other membranous organelles; unicellular;
microscopic; cell wall generally composed of peptidoglycan;
photosynthetic autotrophs, chemosynthetic autotrophs, and heterotrophs.
Archaebacteria
Unicellular; microscopic: peptidoglycan absent in cell walls; differ
biochemically from eubacteria. Methanogenes, extreme halophiles,
extreme thermophiles. Strict anaerobes.
Protista
Mainly unicellular or simple multicellular. Three informal groups. (not
taxa) include protozoa; algae; and slime molds and water molds.
Autotrophs, heterotrophs or both.
Fungi
Heterotrophic; absorb nutrients; do not photosynthesize; cell walls of
chitin
Plantae
Multicellular; photosynthetic; possess multicellular reproductive organs;
alteration of generations; cell walls of cellulose
Animalia
Multicellular heterotrophs; many exhibit tissue differentiation and
complex organ systems; most able to move about by muscular contraction;
specialized nervous tissue coordinates response to stimuli.
Eukaryota
1
In 1937 the French marine biologist Edouard Chatton suggested the term procariotique
(“before nucleus”) to describe bacteria, and the term eucariotique (“true nucleus”) to describe
all other cells. This dichotomy between prokaryotes and eukaryotes is now universally
accepted by biologists as a fundamental evolutionary divergence.
Many biologists now group organisms into two superkingdoms and six kingdoms. The two
superkingdoms are Prokaryota and Eukaryota. The six kingdoms are Eubacteria,
Archaebacteria, Protista, Fungi, Plantae, and Animalia.
A term of algae is not a taxonomical level but a group. Table 1.1 show all living things on the
land, algae group are classified into kingdom Protista. We can put the photosynthetic Protista
(all protists that possess plastids) within the algae group. Cyanobacteria (blue-green algae) are
prokaryotic algae and taxonomically include in the Eubacteria kingdom.
The International Code of Botanical Nomenclature laid down the suffixes to be used for
categories of plant classification and the following are those applicable to algae.
DIVISION (Phylum)—phyta
SUBDIVISION—phytina
CLASS—phyceae
SUBCLASS—phycidae
ORDER—ales
SUBORDER—inales
FAMILY—aceae
GENUS (Normally a Latin name)
SPECIES (Latin)
2
2.1
MORPHOLOGY
Biochemical and structural features of Algae
A number of characteristics have been traditionally used in distinguishing among the major
algal groups. Leading among these are the types of photosynthetic pigments, nature of the cell
covering, and the type of storages reserves present (Table 2.1)
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Chlorophyta
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Rhodophyta
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Ochrophyta
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Dinophyta
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●
●
Haptophyta
●
Cryptophyta
●
Euglenophyta
Glaucophyta
Photosynthetic pigments
chlorophyll a
chlorophyll b
chlorophyll c
phycocyanin
allophycocyanin
phycoeryhtrin
α-carotene
β-carotene
xanthophylls
Storge products
cyanophycin granules,
cyanopytan starch (glycogen)
starch
paramylon
chrysolaminaran
lipids
floridian starch
Cell covering
peptidoglycan
some cellulosic
proteinaceous pellicle
cellulosic plates
CaCO3 scales common
sulfated polysaccarides
some calcified
wall of cellulose
some silica/organic scales
some alginates
some naked
Cyanobacteria
Table 2.1 Predominant photosynthetic pigments, storage products, and cell wall components for the major algal groups
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2.2
Range of Morphological Diversity in Algae
A great deal of variation exists in the morphology of the algal thallus (the algal body),
the most commonly encountered forms of which are described briefly in the following
paragraphs.
Thallus Type in The Algae
1. Unicellular organization
Motile unicellular
(Flagellate unicells)
Rhizopodial type
Non-motile unicellular
Protococcoidal type
Motile colonies
(Flagellate colonies)
2. Colonial organization
Non flagellate coenobia
Non-motile colonies
Tetrasporal forms
Unbranched filaments
3. Filamentous organization
Branching filaments
4. Siphonaceous organization
5. Parenchymatous organization
2.2.1
Unicellular organization
Simple isolated cells are found in all algal groups except the Charophyceae (a green alga) and
Phaeophyceae (brown algae), while in some groups they are the only form represented e.g.
Bacillariophyceae (an Ochrophyta). Some unicellular algae are nonmotile, while others
possess one (or more) of the various means of locomotion found among the algae. Some algae
have locomotory structures known as flagella.
Rhizopodial type: Rhizopodial cells lack rigid cell walls and form cytoplasmic projections;
they are found in the Chrysophyceae (an Ochrophyta—golden-brown algae) Chrysamoeba
(Figure 2.1a).
(b)
(a)
(c)
Figure 2.1 Examples of the rhizopodial and Protococcoidal type of algae; (a) Chrysamoeba (rhizopodial), (b) Chlorella and (c)
Micrasterias (protococcoidal)
Protococcoidal type: Some of the simplest non-motile genera are found in the Cyanobacteria,
Synechoccus, which lacks even an organized nucleus and plastids while simple spherical cells
with a nucleus and plastids containing the characteristic pigments of the group, occur in the
Chlorophyta (Chlorella) (Figure 2.1 b,c)
Flagellate unicells: Motile vegetative cells, moving by
means of flagella, are found in all groups except the
cyanobacteria, Rhodophyta, Phaeophyceae, Charophyceae,
and Bacillariophyceae (diatoms). With a few exceptions
the structure of the flagellate vegetative cells, gametes and
zoospores, is remarkably constant and characteristics. In
the Chlorophyceae (Isokonte) the vegetative cells, the
zoospores and the gametes, all have two equal flagella or
multiples of two, in the dinophyceae there two unequal
flagella running in different planes, in the Chyrsophyceae
one or two and in the pigmented Euglenophyta one long, at
least in some, one short (Figure 2.2).
2.2.2
Figure 2.2 A flagellate unicellular algae
(Phacus) (Euglenophyta)
Colonial Organization
(a)
(b)
Figure 2.3 Flagellate colonies (a) Gonium, (b) Volvox.
Flagellate colonies: Motile flagellate cells aggregate to form simple colonies in some species
of Ceratium (Dinophyta); in this the unmodified cells form into chains after division. In the
some green algae clusters of the cells, bearing siliceous scales or bristles are common. In the
Chlorophyceae, aggregates of cells, embedded in mucilage, from either plate–like colonies
5
(e.g. Gonium) (Figure 2.3a) or mucilage spheres in which the cells are arranged just below the
surface and are interconnected by protoplasmic filaments (e.g. Volvox) (Figure 2.3b).
Coenobia: If a colony assemblage of individual cells form predictable number and
arrangement of cells remain constant throughout the life of the individual, this colony type is
referred to as a coenobium. Depending on the organism, cells in coenobia may be either
flagellated or nonmotile (e.g. Pediastrum) (Figure 2.4).
(b)
(a)
Figure 2.4 Coenobial algae (a) Scenedesmus, (b) Pediastrum. Note that each colony compose of constant number of cells.
Tetrasporal forms: In most groups of algae, non-motile colonies are found in which the cells
are embedded in mucilage; these are known as tetrasporal thalli. The name is came from
Tetraspora (a green algae) in which the cells grouped in fours and no case in there any
connection between these. Tetraspora is a large nonmotile colony. Rather than flagella, each
cell of the vegetative colony bears two pseudocilia, which appear to have been evolutionarily
derived from flagella by reduction. Pseudocilia cannot undergo swimming motions, and their
function in Tetraspora and its relatives is unknown (Hata! Başvuru kaynağı bulunamadı.).
(a)
(b)
Figure 2.5 Tetrasporal forms; (a) Microcystis (blue - green algae) (b) Tetraspora with pseudocilia (green algae).
2.2.3
Filamentous organization
Simple unbranched filaments are found in only a small number of algal groups; they may be
either free-living (e.g. Ulothrix), attached at least initially (e.g. Oedogonium), or aggregated
into colonies (e.g. Nostoc). In the cyanobacteria the filament (trichome) is formed of simple
vegetative cells (e.g. Oscillatoria), the only modification being the development of the apical
cell into a hooded or variously shaped cell. In Spirulina and sometimes in Anabaena, the
filament is wound into a loose or close helix (Figure 2.6a,b)
(a)
(b)
(c)
Figure 2.6 Unbranched filamentous algae; (a) Oscillatoria (blue-green algae), (b) Nostoc (blue-green algae), (c) Ulothrix
(green algae).
Branching filaments: In Cladophora, a
sample branched system found with
basal attachment cells. The branches of
the former end in very characteristic
hairs with bulbous bases and cell
division is of the Oedogonium type.
The Charales (e.g. Chara) have a
complex branching system derived
from apical cells which cut off
segments at the base which form nodal
and internodal cells (Figure 2.7).
Figure 2.7 Branched filamentous algae; (a) Cladophora (b) Chara
(green algae)
2.2.4
Siphonaceous organization
This type of thallus is confined to a few genera in
the Xanthopyceae. The simplest organization is that
of a small unbranched vesicle containing a central
vacuole and peripheral cytoplasm in which the
chloroplasts and nuclei are located and anchored by
branching rhizoid (Vaucheria) (Figure 2.8)
Figure 2.8 Siphonaceous Vaucheria (yellow-green
algae)
7
2.2.5
Parenchymatous organization
Parenchyma is a term used to describe plant
(or algal) tissue that is composed of
relatively undifferentiated, isodiametric
cells generated by a meristem. It results
from cell divisions occurring in three
directions, which gives rise to a threedimensional form. Pseudoparencymatous
algae have thalli that superficially resemble
parenchyma, but which are actually
composed of appressed filaments or
amorphous cell aggregates.
Evolutionarily, parenchymatous growth
habits are thought to represent the most
highly derived state, with
pseudoparencymatous forms representing
an intermediate condition between
filamentous and parenchymatous
conditions.
Figure 2.9 Parenchymatous forms (the brown kelp
Macrocycstis).
Parenchymatous and pseudoparencymatous algae assume a wide range of shapes (sheets,
tubes, stem- and leaf-like arrangements, etc.) and sizes (microscopic to lengths of 50 m or
greater). Ulva (sea lettuce) and Macrocystis (giant kelps) are given for an example of
parenchymatous algae. Macrocystic is reach 50 meter long and construct like a rain forest
under the sea (Figure 5.1, Figure 2.9)
3
REPRODUCTION AND LIFE HISTORY
Algae reproduce by a variety of means, both sexual and asexual. In sexual reproduction,
plasmogamy—fusion of haploid reproductive cells (gametes)—is followed by karyogamy
(nuclear fusion), to form a diploid zygote. The homologous chromosomes contributed by each
of two gametes pair and at some point are partitioned into haploid cells through the process of
meiosis.
Asexual reproduction is a means by which an individual organism can produce additional
copies of itself without such unions of cytoplasmic and nuclear materials or meiosis.
3.1
Asexual reproduction of algae
In general its process the protoplast is released from the algal cell and germinates to form a
new plant.
Cellular bisection: In unicellular flagellates (e.g. Euglena), in the desmids and diatoms,
increase in size is controlled within fairly narrow limits. Division of the cell occurs when a set
size is reached, e.g. in desmids (fam Desmidiaceae) which this size is related to the basic
morphology of the cell. In multicellular algae (or colonies with indeterminate numbers of
cells), this process would lead to growth of individual, i.e., an increase in the size and the
number of its cells.
In diatoms, vegetative division is initiated after a period of increase in cell volume,
accompanied by a growth and sliding apart of the girdle bands; the valves do not increase in
size, and thus cell division is accompanied by a progressive reduction in cell size (Figure 3.1)
Hypotheca
Epitheca
protoplast enlarge
dividing protoplast
completing the valves
Figure 3.1 Diagram of the process developing new valves produced after a diatom cell division. Note that reduction in the mean
cell size as the population increases through time.
In flagellates, vegetative reproduction is brought about by the longitudinal fission of the cell
and the reformation of the organelles, which have not divided e.g. the eyespot. Fission usually
starts at the anterior end and progress downward.
Zoospore and aplanaspore formation: Zoospores are flagellate reproductive cells that may
be produced within vegetative cells or in specialized cells, depending on the organism (Figure
3.2d). Zoospores contain all of the components necessary to form a new individual.
Sometimes, rather than forming flagella, the spores begin their development before being
released from the parental cell of sporangium (Figure 3.2e). These nonmotile spores are
termed aplanaspores.
Autospore or monospore production: Autospores and monospores are also nonmotile
spores, but unlike aplanaspores, lack the capacity to develop into zoospores. Typically look
like miniature versions of the parental cell in which they form (Figure 3.2f). In green algae,
such cells are known as autospore; they are termed monospores in red algae.
9
(f)
(a)
(c)
(b)
(d)
Hormogonia
(h)
(e)
separation disc
(i)
(g)
Figure 3.2 Examples of asexual reproduction in the algae include (a)-(c) cellular bisection; (d) zoospore, (e) aplanaspor, and (f)
autospore production; (g) autocolony formation; (h) fragmentation; and (i) akinetes.
Autocolony formation: In coenobia, each cell goes through a consistent number of successive
divisions giving rise to a miniature version—an autocolony—of the original coenobium
(Figure 3.2g). Depending on the organism, autocolonies may be formed from nonmotile or
motile cells that arrange themselves in a pattern identical to that of the parental cells.
Fragmentation: The simplest methods of the asexual reproduction are those in which division
of the protoplast is not directly involved, but where the individual cells or cell-aggregates are
separated. In Cyanobacteria, Ulatrichales and filamentous Zyngnemaphyceae, fragmentation
of filaments occurs. In these filamentous groups, sections of trichomes are cut off by the
occurrence. The short lengths of trichome thus released are known hormogonia and are often
more actively motile than the parent filament (Figure 3.2h). They arise by separation of
adjacent terminal walls in the tirchome or by the death of certain cells that may become
concave separation disc or necridia
Akinetes: An akinete is a vegetative cell that develops a thickened cell wall and is enlarged,
compared to typical vegetative cells (Figure 3.2i). It is usually a resistant structure with large
amounts of stored food reserves that allow the alga to survive unwanted environmental
conditions, germinating when they improve. Rather than a means of producing additional
copies of the individual during active growth, akinetes represent a type of survival
mechanism.
3.2
Sexual reproduction of algae
Sexual reproduction is not a universal feature in the algae; it has been never demonstrated in
the Cyanobacteria and in many genera of the Chrysophyta and Bacillariophycea it has rarely
been observed, although it is probably a feature of the life history of most species.
Gametes and gamete fusion:
Sexual reproduction involves the combination of nuclear material and frequently cytoplasm,
from two organisms of the same species. The commonest mechanism is the union of two
morphologically identical gametes (isogamy). The gametes may be motile and similar size
and shape fuse with each other. In some species the gametes differ in size or in motility
(anisogamy), and in these the larger or less active gamete generally absorbs the other. The
oogamous state is achieved when one gamete becomes immobile; this egg cell may be
released (e.g. Fucus). Oogamy occurs more widespread in Phaeophyta (brown algae) and
Rhodophyta (red algae). Another type of fusion is illustrated by some diatoms in which
daughter nuclei fuse without release from the parent cell (autogamy).
Life history types:
The union of male and female gametes results in the formation of a zygote and a doubling of
the chromosomal complement to give the diploid state. Before reproduction can occur again
the chromosome number must be halved. There is a three type of life histories depend on
where the meiosis occurs and the type of cells it produces, and whether or not there is more
than one free-living stage present in the life cycle.
Characteristics of the three types are:
1. The major portion (vegetative phase) of the life cycle is spent in the haploid state,
with meiosis taking place upon germination of the zygote (zygotic meiosis) (Figure
3.3).
2. The vegetative phase is diploid, with meiosis giving rise to the haploid gametes
(gametic meiosis) (Figure 3.4).
3. Two or three multicellular phases occur—the gametophyte (typically haploid) and
one (or more, in the case of many red algae) sporophytes (typically diploid). The
gametophyte produces gametes through mitosis, and the sporophyte produces spores
through meiosis (sporic meiosis). This type of life cycle illustrates the phenomenon of
alteration of generations. Alteration of generations in the algae can be isomorphic,
in which the gametophyte and sporophyte are structurally identical, or
heteromorphic, where gametophyte and sporophyte phases are dissimilar (Figure
3.4).
The first life-cycle types are termed haplobiontic (one type of free living individual) the
second type, diplobiontic (two free living stages) and the final type diplohaplontic (two
phases, (diploid and haploid) life cycle. To ovoid the use of what can be confusing, similar
sound terms (haplobiontic, haplontic, haploid, etc.), we can distinguish these life cycle types
by the nature of meiosis (zygotic, gametic, sporic), with the realization that theses terms are
inconsistent in that zygotic refers to the place where meiosis occurs, while gametic and sporic
refer to the nature of the meiotic products.
11
fertilization
+
2N
gametes
zygote
N
meiosis
+
-
meiosis
vegetative cells
Figure 3.3 Zygotic meiosis in the green unicellular flagellate Chlamydomonas.
zygote
N
2N
egg
meiosis
sperm
antheridium
meiosis
oogonium
G
Figure 3.4 Gametic meiosis in a monecious species of the brown rockweed Fucus.
Z
fertilization
-
gametes
+
N
zygote
2N
+ gametophyte
sporophyte
meiosis
spores
meiosis
- gametophyte
S
Figure 3.5 Sporic meiosis in the green alga Ulva. Note that there are two free-living multicellular stages, one haploid one diploid
(alteration of generations).
13
4
CYTOLOGY OF ALGAE
The details of algal cytology have increased enormously during the last two decades largely
from electron microscope studies of cell walls, flagella and cytoplasmic organelles. The ultrastructural studies are also proving invaluable in solving problems of classification and interrelationships of groups.
4.1
Cell walls
A cell wall of an algae composed of relatively pure or mixed carbohydrates. Sometimes this
structure layered with inorganic substances, e.g. silica, calcium or magnesium carbonate.
In many flagellates, zoospores and gametes the enclosing membrane is merely the outermost
layer of cytoplasm (pellicle, periplast). In some algae it is quite flexible, allowing amoeboid
or rhizopodial motion, while in others it has a more definite form owing to underlying
structural elements like Euglena. Even in Euglena there is often considerable change in cell
shape (metaboly) appearing as an inflation passing up and down the cell. In spite of the
cytoplasmic nature of this type of cell membrane, it may have extremely complex striations,
be produced into wings, or be ornamented with a spiral system of nodules.
In most non-motile, unicellular and all the multicellular species the cytoplasm is bounded by a
definite cell wall; it is rarely composed of a single substance and usually has a layered
structure. The outer layer is often mucilaginous or is a thick envelope of mucilage, not
normally visible.
A common constituent of algal cell walls is pectin, but it is more frequently mixed with
cellulose (Chlorophyta, Dinophyta, Rhodophyta, Phaeophyta), with xylose and/or mannose
(Bryopsidophyceae) or silica (Bacillariophcea). In some algae the wall is strengthened with
plates or an encrusting and even penetrating deposit of calcium carbonate (Coccoliths)
(coralline Rhodophyta, Coccolithinae).
4.1.1
Coccoliths:
The scale and coccoliths of the Prymnesiales (a section of the haptophyta), are outer small,
that only electron micrographs reveal the full detail.
Figure 4.1 SEM view of Emiliana huxleyi, showing the coccosphere made up of intreloking coccoliths.
There are two main types of coccolith.
1. Holococcoliths: They are composed of submicroscopic crystals. They are formed
extracellularly.
2. Hetercoccoliths: These are the larger, more obvious coccoliths built up of plates, ribs,
etc., to form a complex amorphous structure (e.g. Emiliana huxleyi, Figure 4.1)
The formation of either holococcoliths or heterococcoliths may in some instance be a valid
taxonomic criterion. The mechanism of coccolith formation is not yet completely understood
but there is evidence that in Coccolithus and Criscosphaera the unmineralised scales and
calcareous coccoliths arise within the bladder of Golgi body. The function of these complex
calcareous plates is unknown. Superficially it would appear that this “heavy skeleton” would
be detrimental to floating organisms. Emiliana huxleyi is a haptophytean can be given as
example for coccolith formation.
Coccoliths probably serve a number of functions, including restriction of access to cells by
pathogenic bacteria and viruses, protection from predation by protozoa, and buoyancy
regulation (by regulated production/loss of heavy coccoliths).
4.2
Flagella
The flagella of algal cells differ in their place of insertion on the cell and in their number,
length, and appendages.
Flagellum consists of two central microtubules surrounded by nine peripheral microtubules
(axoneme) all enclosed in a plasma membrane. This structure is the basic pattern of plant and
animal flagella. The flagella end in the cell, in hollow basal bodies separated from the
flagellum by a diaphragm, but with nine outer tubules continued into wall while the two
centre tubules stop short at the diagram.
Flagella types:
1. Acronematic flagella: This flagellum lacking hair-like appendages (smooth) and its
ended by a fine hair. Acronematic flagellum is usually directed in posterior direction.
2. Pleuronematic flagella: Flagellum bearing lateral hair-like appendages (mastigonem)
and is usually directed in an anterior direction. Pleuronematic flagella are known to be
characteristic of Euglena, Cryptomonas, Synura, Vaucheria.
When these hairs arise unilaterally from the flagellum it is said to be stichonematic; if the
mastigonems arranged in two rows, the term pantonematic is applied. The second flagellum,
when present, is always of the acronematic type.
Pantenomatic
Stichonematic
Acronematic
Two flagellum
15
The flagella of motile cells of most algae have different flagella compositions. If flagella
are equal in length, it’s called isokont flagella. When these flagella unequal in length it is
said to be heterokont flagella.
3. Haptonema: In some mainly marine flagellates, e.g. Chrysochromulina, there is in
addition to the flagella, a structure known as haptonema, which is similar in length to
the flagella or in some species much longer and often with a swollen tip; it is capable
of boing coiled to varying degrees, even right up to the body in the form of a solenoid,
is thinner than the flagella and can serve to anchor the flagellate. Haptonema consists
of three concentric membranes enclosing a ring of six tubules; the outer is threelayered, each layer being approximately 3 nm thick, while the inner are thinner.
Haptonema
Axonem
Typical eukaryotic
flagellum showing
9+2 patterm
Haptonema cross
section
Chrysochromulina chiton
(Chrysophyta)
The type of flagellum appears to be characteristic of taxonomic groups and constant
throughout the group, e.g. one acronematic and one pleuronematic in the Phaeophyta and
Xantophyta and two acronematic in the Chlorophyta. In the Chrysophyta the flagella bear
mastigonems while those of the Haptophyta are smooth.
Flagellu
Basal region
Nucleus
a
f
b
c
e
d
g
h
Figure 4.2 Behaviour of basal region and flagella during meiosis
a) A cell with flagellum b) withdraw flagellum into protoplasm c) Disappearing of axonema d) Bazal region goes near to nucleus
e) Dividing of basal area f) Anaphase g) Telophase h) Construction of axonema
4.3
Plastids (chromatophore = chloroplast)
The most obvious feature of algal cells is the plastid, the form of which is a useful criterion of
taxonomic affinity when combined with other features. Shape of chromathophores may be
discoid, plate, simple, lobed, spiral, branched or very complex structure. Electron microscopic
studies show a chromatophore membrane of unit membrane structure. Inside the
chromatophore membrane further stacks of membranes occur, each of which is a paired
structure, joined at the ends form thylakoids. In Rhodophyta, Chlorophyta and Charophyta
chromotophore membrane consists of two layers, other algal eucaryotic algal groups in
addition to this two layer there is a chloroplast endoplasmic reticulum (CER). The CER is
an evagination of the outer nuclear membrane, extending to surrounds the chloroplasts and
also pyrenoid, if present.
Thylakoids are the photosynthetic lamella which chlorophyll containing structures and
granules, lipid droplets and starch grains are found in the matrix. Between the thylakoids is
the matrix (or stroma) and this, the stacks of thylakoids and the membrane, form the algal
chromatophore. In most algae there are no grana comparable to those of the higher plants, but
in the desmid. Thylakoids are central of the photosynthetic reactions. They are the sites of
chlorophyll a. In Cyanobacteria and Rhodophyta accessory pigments also occurs in thylakoid
surfaces in the form of small particles, the phycobilisomes. In most algae the eyespots and
pyrenoids are associated with plastids.
4.4
Algal pigments
Algal pigments can be divided into three groups, differing widely in chemical composition.

Chlorophylls

Carotenoids (carotenes and xantophyllls)

Phycobilins
4.4.1
Chlorophyll pigments
Fat soluble chlorophylls are tetrapyrrolic molecules with a central magnesium atom and two
ester groups. Five chlorophylls have been isolated but only one, chlorophyll a, is common to
all algal groups. There is a similarity between Chlorophyta and higher plants (which have
only chlorophylls a and b). Chlorophylls are characterized by strong absorption of red (650680 nm) and blue (400-450 nm). The chlorophyll molecule is loosely associated with protein
molecules in the plastids.
Chlorophyll a is the main photosynthetic pigment that initiates the light-dependent reactions
of photosynthesis. Chlorophyll b is an accessory pigment that also participates in
photosynthesis. It differs from chlorophyll a only in a functional group on the porhpyrin ring:
the methyl group (—CH3) in chlorophyll a is replaced in chlorophyll b by a terminal carbonyl
group (—CHO). This difference shifts the wavelengths of light absorbed and reflected by
chlorophyll b, making it yellow-green, whereas chlorophyll a is bright green.
17
chlorophyll a
(reaction center)
incoming light
Accessory
pigments
Figure 4.3 Energy from photons bounces among pigment molecules until trapped by chlorophyll a molecule.
CH2
CH3
in chlorophyll a
in chlorophyll b
CHO
CH3
CH2 CH3
N
N
Mg
N
H
Porphyrin ring
(absorbs light)
N
CH3
CH3
CH2
H
CH2
O
C
O
H
C
O
OCH3
O
CH3
CH3
CH3 H
CH3 H
H
CH3
Hydrocarbon side chain
Figure 4.4 Chlorophyll structure. Chlorophyll consists of a porphyrin ring and a hydrocarbon side chain. The porpyrin ring, with a
magnesium atom in its center, contains a system of alternating double and single bonds: these are commonly
found in molecules that strongly absorb visible light. At the top right corner of the diagram methyl group (—CH3)
distinguishes chlorophyll a from chlorophyll b, which has a carbonyl group (—CHO) in this position.
4.4.2
Carotenoid pigments
The other fat-soluble group of pigments comprises the yellow- or red- colored carotenoids,
consisting of carotenes, xantophylls (oxycarotenes) and carotenoid acids. They absorb blue
and green light (430-500 nm). Transmit yellow and red, and are weakly fluorescent.
Carotenes are unsaturated long-chain hydrocarbon molecules. The structure is a polyene
chain, i.e. having alternate double and single bonds; light absorption is due to these bonds and
the greater the number of double bonds the redder color. The ends of the chains of molecules
are coiled into rings and like the chlorophylls they are loosely bound with proteins in the
plastids. The β-carotene content of algae is generally less (5-20 percent) in the Chlorophyta
than in the higher plants (30 percent of total pigment). β-carotene occurs in nearly all
photosynthetic algae, and is particularly important as the main source of provitamin A,
required by animals for synthesis of the visual pigment rhodopsin and in the regulation of
genes involved in limb and skin development. These pigments harvest blue wavelengths of
light that are not directly absorbed by chlorophyll a. In addition, carotenoids also provide
protection from harmful photooxidation. Their association with chlorophyll prevents the
formation of highly reactive oxygen radicals that could otherwise cause irreparable damage to
lipids, proteins, and other molecules.
The xanthophylls are long chain hydrocarbons of the carotene type but with oxygen atoms
forming hydroxyl (—OH) structures (Figure 4.5c).
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3 CH3
β-carotene
(a)
CH3
CH3
CH3
CH3
CH3
CH2-OH
CH3
provitamin A
(b)
CH3
CH3 CH3
CH3
CH3
CH3
OH
(c)
4.4.3
CH3
zeaxanthin
CH3
OH
CH3 CH3
Different from
β-carotene
Figure 4.5 Structures of (a) βcarotene, (b) provitamin A,
and (c) zeaxanthin.
Provitamin A is formed by
splitting β-carotene into two
equal parts (at arrow).
Zeaxanthin is a common
xanthophyll, and is also
synthesized from βcarotene.
Phycobilin pigments
A group of water-soluble pigments (phycobilins) are found in the Rhodophyta, Cyanobacteria,
and Cryptophyta. There are two types of phycobilins:
Phycocyanin: Transmitting blue light and absorbing green, yellow and red.
Phycoeryhtrin: Transmitting red light, and absorbing blue green and yellow.
Allophycocyanin: Transmitting and absorption features such as Phycocyanin but
structurally different
19
Phycobilin pigments found in the phycobilisomes—located on thylakoids— captured light
energy is efficiently passed to phycocyanin and allophycocyanin, and finally to chlorophyll a,
allowing the harvesting of light energy of light energy that is otherwise inaccessible to
chlorophyll. The components of phycobilisomes are arranged in such a way as to maximize
energy transfer to chlorophyll a. On the basis of absorbance characteristics, energy transfer is
expected to occur from phycoeryhtrin to phycocyanin to allophycocyanin to chlorophyll a in
photosystem II (Figure 4.8)
Models of the structure of a phycobilisomes show an outer surface consisting of fingerlike
stacks (rods) composed of several phycoeryhtrin molecules, an inner layer of phycocyanin,
and a core of allophycocyanin molecules.
Any algae group (e.g. cyanobacteria) having chlorophyll b do not produce phycobilin
pigments.
4.4.4
Chromatic adaptation
Some cyanobacteria can adjust their pigment composition in response to changes in light
quality. Exposure to red light increases synthesis of the blue-colored phycocyanin, whereas
exposure to green light increases synthesis of phycoeryhtrin. Than some cyanobacteria can
undergo a color change to red under green light, and change to blue-green pigmentation in red
light. Such alteration of pigment composition, known as chromatic adaptation, provides an
adaptive advantage to cyanobacteria whose light environment may change over their lifetime.
Light energy is passing through water is differentially absorbed, the red first then green and
finally blue, so that the Rhodophyta (red algae), living generally at the greatest depth, have
their maximum absorption in the green, which is the only light energy available in any
quantity at such depth; the intermediate Phaeophyceans (brown algae in phylum Ochrophyta)
absorb green-yellow-orange, which penetrates to intermediate depths and the Chlorophyta in
the blue and red, both of which are available at the surface.
phycoeryhtrin
phycocyanin
allophycocyanin
thylakoid
Figure 4.6 A model of the phycobilisomes. Note the positions of the there types of phycobilin pigment molecules relative to the
energy transfer incated in the figure The pigments are held together by linker proteins (striped boxes).
1.0
Chlorophyll b
Absorbance
0.8
0.6
Carotenoids
Chlorophyll a
0.4
0.2
400
600
500
700
Wavelength (nm)
Figure 4.7 Absorption spectra for chlorophyll
a, carotenoids, and chlorophyll b. The
latter two pigment types act as
“accessory” pigment, absorbing
additional wavelengths of light and
passing the energy along to chlorophyll
a.
hv
PHYCOERYTHRIN
(A 545nm — F 575nm)
PHYCOCYANIN
(A 555nm — F 636nm)
ALLOPHYCOCYANIN
(A 650nm — F 636nm
Aggregated F 675nm)
CHLOROPHYLL a
(A 670nm — F 685nm)
4.4.5
Figure 4.8 In phycobilisomes light energy is
transferred from phycoeryhtrin to
phycocyanin to allophycocyanin to and
finally to chlorophyll a in thylakoids.
Endosymbiosis and origin of plastids
We have two definition of symbiosis, one of them is original definition “living together of
dissimilar organisms” and a more modern one, “living together in physical contact of
organisms of different species” as well as extending the definition to intracellular
associations.
Phagotrophy (the ingestion of particulate food) is regarded as the major mechanism by which
algal plastids were acquired, and it has been proposed that the earliest photosynthetic
eukaryotes in all of the major algal lineages were phagotrophic.
The process of incorporation and integration of bacterial endosimbiyonts (photosynthetic
cyanobacteria blue-green algae) within host cells to form ekaryotic, organelle-containing
21
entities is called primary endosymbiosis (Hata! Başvuru kaynağı bulunamadı.) The
process by which eukaryotic cells are taken up and integrated into host cell is known
secondary endosymbiosis (Hata! Başvuru kaynağı bulunamadı.).
Red algae (Rhodophyta) and green algae (Chlorophyta) have plastids that arisen by primary
endosymbiosis. Their plastid structure supports this theory. They have only two layer of
membrane, but the other algal groups have more than two layers. Algal groups those plastids
arisen by secondary endosymbiosis evolved from red algae or green algae.
Following structure of plastids supports endosymbiosis theory.
1. The DNA of algal plastids has ring shaped nucleotids. The plastid transcription and
translation system is very similar to that of bacteria.
2. Ribosomal sizes (70 S) and the spectrum of antibiotic sensitivities very similar to tahat
of bacteria.
3. Membranes of plastids compose of more than one layer.
Similarities in plastid and eubacterial structures indicate that all modran plastids are of
cyanobacterial origin.
photosynthetic
prokaryote
free-living bacterium
N
phagotrophic
eukaryote
photosynthetic
eukaryote/
primary plastid
C
phagotrophic
eukaryote
N
N
2nd phagotrophic
eukaryote
N'
Mitochondrion
or
plastid
C
N
2nd photosynthetic
eukaryote /
secondary plastid
N
N'
Figure 4.9 A diagrammatic representation of the process of
primary endosymbiosis, in which a free living bacterium is
incorporated into a phagotrophic eukaryotic cell and
eventually transformed into an organelle.
Figure 4.10 Diagram of secondary endosymbiosis, whereby a
eukaryote that earlier acquired a plastid via primary
endosymbiosis is itself taken up by a second eukaryote.
4.5
Pyrenoids
In most algae pyrenoids are associated with the chromatophores. In most green algae the
plastids contain one or more specially differentiated regions called pyrenoids. In the green
algae the pyrenoid is the site of the starch formation, one or more starch grains forming within
the chloroplast closely appressed to the surface of the pyrenoid. It has been suggested that the
pyrenoid is the region of temporary storage for early products of photosynthesis that, upon
overproduction, are converted into starch.
4.6
Mitochondria
Mitochondria are basically similar in all groups, and certainly function similarly as sites of
enzyme action in Krebs cycle, amino acid intreconversion and protein synthesis. They are
bounded by a double membrane, the inner produced into folds (cristae), projecting into the
lumen which contains a structureless or slightly granular matrix. In certain cells the number of
mitochondria appears to be relatively constant. Cells of Cyanobacteria do not posses
mitochondria.
Among the various algal groups, three types of mitochondria have been noted; they are
distinguished by morphology of the cristae (Table 4.1). Some algal groups (ochrophytes,
dinoflagellates, haptophyta) have mitochondria with tubular cristae, whereas others
(glaucophytes, cryptomonads, red algae, and green algae) have flattened, plate-like cristae,
while euglenoids have discoid cristae. It has been proposed that the mitochondrion arose once
in common ancestor of all extant eukaryotes, possibly at the same time as the nucleus.
Mitochondria have long been known to posses eubacterial-like DNA and transcription and
translation systems, including similarly sized ribosomes. Also, infoldings of the cell
membrane similar to the cristae of mitochondria characterize certain alpha proteobacteria
(purple bacteria), where they function in photosynthesis. These similarities, together with
comparative molecular sequence evidence, particularly for 70 S ribosome genes, strongly
support the hypothesis that mitochondria were once free-living photosynthetic proteobacteria
that became endosymbiotically incorporated into the host cells, lost photosynthetic capacity,
and assumed the specialized function of aerobic respiration.
Table 4.1 Characteristics of the mitochondria and endosymbiotic origin of plastids of the major eukaryotic algal groups
Group
Mitochondrial cristae
Plastid origin(s)
Glaucophytes (Glaucophyta)
flattened
primary
Cryptomonads (Cryptophyta)
flattened
secondary (red)
Red algae (Rhodophyta)
flattened
primary
Green algae (Chlorophyta)
flattened
primary
Euglenoids (Euglenophyta)
disk-shaped
secondary (green)
Haptophytes (Haptophyta)
tubular
secondary (red)
Dinoflagellates (Dinophyta)
tubular
mainly tertiary (various sources)
Ochrophytes (Ochrophyta)
tubular
secondary (red)
4.7
Eyespots (stigma)
Many motile algae have eyespots. Eyespot may detect the direction of the source of light and
distinguish light intensity. The eyespot of some flagellates is situated beneath the
chromatophore membrane. It consists of clusters of carotenoid-lipid granules each surrounded
23
by a membrane. The eyespot of Euglena is not within the chromatophore, a feature which can
be seen by light microscopy. Euglena eyespot granules also containing a special pigment
(astaxantin). Astaxanthin (derivative of β-carotene) is a pigment occurring in several animals.
This pigment characteristic of Euglena gives a special structure that both plants and animals.
4.8
Golgi apparatus
These are present in all algal cells except Cyanobacteria and are fairly easily recognizable in
sections under the electron microscope. They may be found in the region of the nucleus (e.g.
in Chlamydomonas) or associated with flagellar basis (e.g. in Chrysochromulina) and are
composed of stacks of flat vesicles. They are frequently accompanied by smooth, circular or
oval vesicles which form at the edges of the dictiyosome. The Golgi apparatus of diatoms
produce vesicles which are involved in wall formation. Heterococcolids of Haptophyta body
wall formed internally by the Golgi apparatus. Bioluminescent dinoflagellates posses’
spherical structure derived from the Golgi apparatus. These vesicles contain luciferin,
luciferas and some cases luciferin-binding protein.
5
5.1
DIVERSITY OF THE ALGAE
Algae in the marine habitat
On land the largest and most striking plants are the trees. Together with their herbaceous
relatives, their foliage makes green the most conspicuous color of the biosphere. Underwater
there are “trees” of similar height that are less widely valuable because most humans spend
little time in their world. Brown undulating forests of 50-meter long giant kelps, as tall and
crowded as their terrestrial counterparts, dominate significant stretches of submerged
temperate coastlines. Like trees, kelps use photosynthesis
Figure 5.1 Kelp forest off the Chilean
coast. Predominant alga pictured is
Macrocystis sp.
To convert the energy of sunlight into chemical energy, but the green of their chlorophyll is
masked by the large amounts of brown pigments. These accessory pigments aid in the
collection of light not absorbed directly by chlorophyll molecules and channel the light energy
to chlorophyll a (the only pigment that is able to effectively convert energy of absorbed light
into high energy bonds of organic molecules. This is necessary because as light passes
through water, the longer wavelengths are filtered out first, such that eventually all that
remains is a faint blue-green light that cannot be absorbed by chlorophyll.
The depth record for algae is held by dark purple-colored crusts of yet unnamed red algae
discovered in tropical waters by phycologists using submersibles. These organisms live at
depth greater than 250 meters, where the light intensity is only 0.0005% that of surface light.
The accessory pigments of these algae are essential for the survival of photosynthetic in such
low-irradiance environments. In contrast, algae that live in high-irradiance habitats typically
have pigments that help protect against photodamage. It is the composition and amounts of
accessory and protective photosynthetic pigments that give algae their wide variety of colors
and, for several algal groups, their common names such as the brown algae, red algae, and
green algae. But attempting to identify a particular alga by color alone could be problematic,
25
since, for example, there are red-colored green algae and brown of purple-colored red algae;
other characteristics and features must also be considered.
The rocky or sandy shallows of temperate and tropical oceans harbor a vast array of brown,
red, and green algal growths that many form thin and sometimes slippery films on rocks; or
miniature jointed shrubs armored with limestone. Tropical corals share the sea bottom with
intracellular tenants (microscopic golden algal cells known as zooxanthellae) that generate
food and oxygen in exchange for metabolic by-products (carbon dioxide and ammonia)
released by coral cells. Zooxanthellae help to corals to live in the typically low-nutrient
conditions of tropical waters. Because of their obligate association with these photosynthetic
algae, reef-building corals are limited to shallow, well illuminated waters less than 20meters
or so in depth.
Figure 5.2 Hydra containing endosymbiotic green algae
known as zoochlorellae.
Beneficial algae also occur within the cells and tissues of wide variety of other marine
animals such as nudibrahchs, anemones, giant clams, ascidians, and sponges, as well as inside
the cells of simple organism known as protists.
Algal aggregations and other large group of algae construct importance level of
phytoplankton (free-living organisms that lack of swimming organelles). Although
individually visible to humans only with the aid of a microscope, large populations can give
ocean waters green or rusty colors. Color variations reflect differences in the types and
amounts of blue-green, red, orange, and golden accessory pigments accompanying the green
of chlorophyll.
Population of marine phytoplankton can become so large that they are detectable by satellite
remote sensing technology. Such blooms are in fact one of the more dramatic vegetational
features of the planet when viewed from space. Collectively marine microalgae have been
modifying the earth’s atmosphere for more than 2.7 billion years, and they continue to exert a
powerful influence on modern atmospheric chemistry and biochemical cycling of carbon,
sulfur, nitrogen, phosphorus, and other elements. Hundreds of millions of years’ worth of past
phytoplankton growth and sedimentation have generated important oil and limestone deposits.
Species of Halophyta phylum generated chalk cliffs with their calcium carbonate coccoliths
during Late Cretaceous and the name of time “Cretaceous” (chalk era) come from algae that
lived during those times.
5.2
The Algae of Freshwater
Freshwater lakes, ponds and streams contain planktonic and attached forms microalgae.
(b)
(a)
Figure 5.3 Some freshwater algae. (a) Chara sp., a green alga
commonly called a stonewort, is closely related to plants.
Chara is widely distributed in fresh water, where it grows to
30 cm or longer. (b) LM of a widely distributed desmid
(Micrasterias sp.), a unicellular green alga with mirror-image
halves. (c) LM of Volvox colonies, each composed of 50.000
cells. New colonies can be observed inside the paternal
colonies, which eventually break apart to release them.
(c)
The life form of algae according to their environment and features
Planktonic: free-floating, or suspended in the water column.
Benthic: Having to do with the benthos—the bottom of a lake, stream or marine
system.
Epiphytic: living on the surfaces of plants or algae.
Epilithic: living on the surfaces on rocks.
Epipelic: living on the surfaces of mud or sand.
Epizooic: living on the surface on animals.
Endozooic: living within an animal’s body.
Although not exhibiting the huge size range of their marine relatives, freshwater algae display
a wide diversity of form and function. As in the oceans, it is not uncommon to find that
certain photosynthetic freshwater algae colonize the cells and tissues of protozoa or
coelenterates like the familiar Hydra. Cyanobacteria living within the tissues of water ferns
27
can be a major to the nitrogen economy of rice cultivation in paddies and influence the
nutrition of millions of human beings. Freshwater phytoplankton and periphyton (also known
as benthic algae) form the base of the aquatic food chain, without which freshwater fisheries
could not exist. In addition to oceanic and freshwater environments, some algae have adapted
to extreme habitats such as hot springs and salty lakes
5.3
Algal blooms
Blooms of microscopic algae occur in marine and freshwaters, often in response to pollution
with nutrients such as nitrogen and/or phosphate. Nutrient pollution can usually be traced to
human activities, such as discharge of effluents containing sewage or industrial wastes, or the
use of agricultural fertilizers. Water transparency may become so reduced that organisms such
as corals, aquatic plants, and periphyton no longer receive sufficient light for photosynthesis.
It has been estimated that 50% or more of marine and freshwater algal blooms produce
poisons that effect neuromuscular systems, are toxic to the liver, or are carcinogenic
vertebrates. These toxins can cause massive fish kills, death of birds, cattle, dogs and other
animals, and serious illness, or death, in humans.
(a)
Figure 5.4 Algal blooms (a) in pacific ocean consisting a
dinoflagellate Noctiluca (b) in the Gippsland Lakes
(Australia) consisting Nodularia spumigens, cyanobacteria.
5.4
(b)
Terrestrial algae
A considerable number of algae have adapted to life on land, such as those occurring in the
snows of mountain ranges, in “cryptobiotic crusts” typical of desert and grassland soils, or
embedded within surfaces of rocks in deserts, polar regions and other biomes. The activities
of soil and rock algae are thought to enhance soil formation and water retention, increase the
availability of nutrients for plants growing nearby, and minimize soil erosion.
Several species of terrestrial algae, together with fungi, form the distinctive life-forms known
as lichens. Lichens are ecologically important because of their role as pioneers in early stages
of succession, where they help to convert rock into soil, slowly dissolving it with excreted
acids. Lichens also help to stabilize fragile desert soil and are used as living barometers of air
quality because of their sensitivity to air pollution.
Some terrestrial algae occur in surprising places. For example, algae can impart a greenish
cast to the fur of giant sloths and sometimes live within the hollow hairs of polar bears. Also
pink color of flamingos is due to a red-colored algal accessory (carotenoid) pigment
consumed as they feed. Algae also occur regularly within the tissues of various plants.
5.5
Human uses of algae
For millennia people throughout the world have collected algae for food, fodder (food for
farm animals), or fertilizer. More recently algae have begun to play important roles in
biotechnology. For example, they have been used to absorb excess nutrients from effluents,
thereby reducing nutrient pollution in lakes and streams. Algae also generate industrially
useful biomolecules, and serve as a human food source, either directly or indirectly, by
supporting aquaculture of shrimp and other aquatic animals.
Algae have provided science with uniquely advantageous model systems for the study of
photosynthesis and other molecular, biochemical, and cellular-level phenomena of wider
importance. Examples include Melvin Clavin’s explanation of light-independent (“dark”)
reactions of photosynthesis in the green alga Chlorella. Studies of algae have been essential to
our understanding of basic photosynthetic processes, and they continue to break new
conceptual ground.
5.6
Variations in algal nutrition
The old concept of algae as a simple phototrophic group has now to be modified.
Photoautotrophy, they synthesis of the essential metabolites from simple chemicals and light
energy, is however, still a feature of many algae (e.g. many Chlorophyta, diatoms and
Cyanobacteria) and is obligate. Carbon fixation is important event for autotrophic species,
that the transformation of dissolved inorganic carbon, such as carbon dioxide or bicarbonate
ion, into an organic form. Photosynthesis is also a kind of carbon fixation:
6CO2
Carbon
dioxide
+ 12H2O ————→
Water
Light energy
C6H12O6
Glucose
+ 6O2
Oxygen
+ 6H2O
Water
Chlorophyll
The majority of algal groups contain heterotrophic species that obtain organic carbon from the
external environment either by ingesting particles by a ingesting particles by a process known
as phagotrophy, or through uptake of dissolved organic compounds, an ability termed
osmotrophy. Some algae, referred to as auxotrophs, are incapable of synthesizing certain
essential vitamins and hence must import them. Only there vitamins are known to be required
by auxotrophic algae—biotin (vitamin H), thiamine (B1), and cobalamin (B12).
Numerous algae exhibit a mixed mode of nutrition; that is, photosynthesis in addition to
osmotrophy and/or phagotrophy—an ability termed mixotrophy. Mixotrophic organisms (e.g.
Euglena spp.) have a tendency to metabolize photographically in the light and
heterotrophically in the dark; these may be termed amphitrophic. Some algae (e.g.
Ochromonas sp.) possess pigments in such small amount that although they can
photosynthesize this alone is not sufficient for growth. Another example of mixotrophy in a
nonflagellate alga is the uptake of dissolved amino acids by rhizoids of the green seaweed
Caulerpa.
In addition to inorganic and organic components, phototrophic algae require an external
source of energy. This energy is provided by light of wavelengths between 400 and 700 nm
and it is absorbed by the photosynthetic pigments located, usually, but not always, in distinct
plastids.
29
General nutrition types:
Photoautotrophy: Organisms that obtains its organic nutrients by means of photosynthesis:
obligate photoautotrophs are restricted to this form of nutrition (Photoautotrophic).
Chemoautotrophy: Organisms using inorganic sources of carbon, nitrogen, etc., as starting
material of biosynthesis, and an inorganic chemical energy source (Chemoautotrophic).
Photoheterotrophy: A form of nutrition in which light is captured and used as an energy
source by a pigmented alga, which, at the same time, takes up dissolved organic compounds
from the environments (Photoheterotrophic) (e.g. Chrycochromulina sp., a marine and
freshwater Haptophyta)
Chemoheterotrophy = Chemotrophy: Organism obtaining energy by taking in and
oxidizing chemical components by the breakdown of complex organic pounds (food).
Mixotrophy: A form of nutrition in which both autotrophy and heterotrophy may be utilized,
depending on the availability of resources.
Auxotrophy: The nutritional requirement for one or more vitamins (auxotrophic).
5.7
Summaries of the nine algal phyla
Phylum Cyanobacteria (Cyanophyta, blue-green algae).
This phylum is a well-defined group of eubacteria. Cyanobacteria include unicellular
and filamentous forms, some having specialized cells. Uniquely among bacteria,
cyanobacteria produce oxygen as a product of photosynthesis. Chlorophyll a and accessory
and protective pigments (phycobilins and carotenoids) are present, associated with
membranous thylakoids. Some members of the group (prochlorophytes) also possess
chlorophyll b. The photosynthetic storage products include an α-1,4-glucan known as
cyanophytan starch. Among autotrophs, cyanobacterial cells are unique in being prokaryotic
in organization, hence typical eukaryotic flagella and organelles (chloroplasts. mitochondria
and nuclei) are lacking. Cyanobacteria are common and diverse both freshwater and the sea.
Sexual reproduction of the typical eukaryotic type, involving gamete fusion, is not present.
Phylum Glaucophyta
Glaucophytes includes several eukaryotes having blue-green plastids (known as
cyanelles or cyanellae) that differ from other plastids and resemble cyanobacteria in several
ways including the possession of a thin peptidoglycan wall. The cyanelles/plastids possess
chlorophyll a and phycobilins, as well as carotenoids. Granules of true starch (an α-1,4-glucan
are produced in the cytoplasm. There are about nine genera, all freshwater. Sexual
reproduction is unknown. This group has sometimes been included within the red algae.
Phylum Euglenophyta
This phylum contains euglenoid flagellates, which occur as unicells or colonies. There
are about 40 genera, two thirds of which are heterotrophic, some having colorless plastids and
some lacking plastids altogether. One third have green plastids with chlorophyll a and the
accessory pigment chlorophyll b as well as the carotenoids that are typical of green algae, and
are capable of photosynthesis. Cell walls are lacking, but there is a protein-rich pellicle
beneath the cell membrane. One to several flagella may be present, and non flagellate cells
can undergo a type of motion involving changes in cell shape. The storage material is not
starch but rather a β-1,3,-linked glucan known as paramylon, which occurs as granules in the
cytoplasm of pigmented as well as most colorless forms. Most of the 900 or so species are
freshwater, and sexual reproduction is not known.
Phylum Cryptophyta
Cryptophyta contains the unicellular cryptomonad flagellates, with 12-13 genera. A
few are colorless, but most possess various colored plastids with chlorophyll a. Chlorophyll c,
carotenoids, and phycobilins constitute the accessory pigments. Alloxanthin is a xantophyll
that is unique to cryptomonads. There is not a typical cell wall. Rather, rigid proteinaceous
plates of various shapes occur beneath the cell membrane. Cells can be recognized by their
typical flattened asymmetrical shape and the two anterior, slightly unequal flagella. The
storage carbohydrate is starch, located in a space between plastid membranes. There are about
100 freshwater species and about 100 marine species. There is some evidence for sexual
reproduction.
Phylum Haptophyta
Haptophytes comprises unicellular flagellates or nonflagellate unicells or colonies that
have flagellate life-history stages. The photosynthetic pigments include chlorophyll a, and
accessory and photoprotective pigments including chlorophyll c and caretonoids such as
fucoxanthin. Species vary in the form of chlorophyll c and presence of absence and form of
fucoxanthin. There is a β-1,3-glucan storage material. Two flagella and nearby sturctire
known as a haptonema characterize the apices of flagellates. Many species, known as
coccolithophorids, produce calcium carbonate-rich scales called coccoliths. The 300 species
are primarily marine. Sexual reproduction, known in some cases to involve heteromorphic
alteration of generations, is widespread.
Phylum Dinophyta
This phylum includes the dinoflagellates, mostly unicellular flagellates having two
dissimilar flagella. About one half of the 550 genera are colorless heterotrophs; the rest
possess plastids that vary significantly in pigment composition and type of Rubisco, the
enzyme responsible for photosynthetic carbon fixation. Pigmentation is usually golden-brown,
reflecting the common occurrence of the unique accessory xanthophyll peridinin, but green
and other colors are known. True starch granules occur in the cytoplasm. The cell covering is
a peripheral layer of membrane-bound vesicles, which in many cases enclose cellulosic plates.
Of the 2000-4000 species, the vast majority are marine; only about 220freshwater forms are
recognized. Symbiotic dinoflagellates known as zooxanthellae occur in reef-forming corals
and other marine invertebrates. Sexual production is known.
Phylum Ochrophyta
This phylum includes diatoms, chrysophyceans, phaeophyceans (brown algae), and
some other groups. Members range in size from microscopic unicells to giant kelps (60 m in
length) having considerable tissue differentiation. Chlorophyll a is present in most
ochrophytes, but some colorless heterotrophic forms also occur. I the pigmented forms,
dominant accessory and photoprotective pigments may include chlorophyll c and carotenoids
such as fucoxanthin or vaucherianxanthin. The food reserve is cytoplasmic lipid droplets
and/or a soluble carbohydrate (β-1,3-glucan chrysolaminaran or laminaran) which occurs in
cytoplasmic vacuoles. There are usually two heteromorphic flagella, one bearing many
distinctive three-piece hairs known as mastigonemes. Cell coverings vary widely and include
silica scales and enclosures as well as cellulose cell walls. There are more than 250genera and
10.000 species of extant diatoms alone. Some groups of the Ochrophyta are primarily
freshwater, some are primarily marine, and some, such diatoms, are common in both fresh
and salt water. The brown algae known as the giant kelps are the largest of all the algae.
Sexual reproduction is common, and several types of life cycles occur.
31
Phylum Rhodophyta (Red algae)
Red algae have members that occur as unicells, simple filaments, or complex
filamentous aggregations. Pigments are present in all except certain parasitic forms, and
include chlorophyll a together with accessory phycobilins and carotenoids. Flagella are not
present. The cytoplasmic carbohydrate food reserve is granular Floridian starch, an α-1,4glucan. Cell walls are loosely constructed of cellulose and sulfated polygalactans, and some
are impregnated with calcium carbonate. The calcified red algae known as corallines are
widespread and ecologically significant in coral reef systems. The 4000-6000 species are
primarly marine, favoring warm tropical waters. Sexual reproduction is common, as is
alteration of generations. A triphasic life history characterizes most red algae and is unique
to this group.
Phylum Chlorophyta (Green algae)
Green algae have unicellular or multicellular thalli. Some are flagellates, and others
produce reproductive cells, the majority of which are biflagellate. In addition to chlorophyll a,
the pigments chlorophyll b, β-carotene, and other carotenoids occur in plastids. Uniquely,
starch is produced within plastids of green algae (and land plants).Cell walls of some are
cellulosic as in land plants, but the walls of other green algae are composed of different
polymer, and some are calcified. Early divergent flagellates and one multicellular clade (the
ulvophycean green seaweeds) are primarily marine, whereas other groups are primarily
terrestrial or freshwater. One of the freshwater lineages (the charophyceans) gave rise to the
land plants (embryophytes). There are about 17,000 species. Sexual reproduction is common,
and all three major types of life cycle occur.
6
6.1
GENERAL FEATURES OF ALGAL DIVISIONS
Division CYANOBACTERIA (Blue-green algae)
Cyanobacteria, also known as chloroxybacteria, blue-green algae, or Cyanophyta, are
significant for many reasons. Cyanobacteria were the dominant forms of life on earth for more
than 1.9 billion years. They were the most ancient oxygen-producing photo synthesizers; the
first to produce chlorophylls a and b as well as a variety of accessory photosynthetic
pigments; producer of massive carbonate formations in shallow waters during the
Precambrian period; and the earliest (Precambrian) terrestrial autotorophs. The chloroplasts of
eukaryotic algae and plants are descended from Cyanobacteria.
The oldest fossils attributed to cyanobacteria are 3.5 billion-year-old remains from the Apex
Basalt, a geological deposit in western Australia. Stromatolite is the fossilized remains of a
colony or mat of bacteria cyanobacteria that normally exhibits either a domed or a columnlike shape, and the sediment in which it lies may be marked with fine concentric bands
(Figure 6.1). The layers were produced as calcium carbonate precipitated over the growing
mat of bacterial filaments; photosynthesis in the bacteria depleted carbon dioxide in the
surrounding water, initiating the precipitation. The minerals, along with grains of sediment
precipitating from the water, were then trapped within the sticky layer of mucilage that
surrounds the bacterial colonies, which then continued to grow upwards through the sediment
to form a new layer.
Figure 6.1 A stromatolite that has been split open, revealing the layering typical of
these formations
Cyanobacteria contain chlorophyll a, which differs from the chlorophyll of those bacteria,
which are photosynthetic, and also free oxygen is liberated in blue-green algal photosynthesis
but not in that of bacteria.
The origins of the blue-green algae are unclear. It is attempting to assign them to an
evolutionary path parallel to that of the photosynthetic bacteria, but as the group that evolved
the pathway for evolution of oxygen. No transition forms between these two types of
photosynthesis have been found, however, and thus there are no likely candidates for the
ancestral of the blue-green algae.
33
6.1.1
Habitat
Blue green algae are very common in waters of a great range of salinity and temperature, and
they occur in and on the soil and also on rocks and in their fissures. Little recorded the
occurrence of Gleocapsa, Nostoc in the supralittoral zone of marine shores. A number have
been recovered from the atmosphere. In general blue-green algae seem to be more abundant in
neutral or slightly alkaline habitats, although some (Chroococcus) are said to be to occur in
bog waters at pH 4. Blue-green algae are absent from waters whose pH was less than 4 or 5,
while certain eukaryotic algae are present. Blue-green algae are both planktonic and benthic.
Some planktonic forms for example, Microsystis aeruginosa, Anabaena flos-aquae,
Trichodesmium erythraeum. The last species common in tropical waters, including the Red
Sea (which probably was so named because of the colour of the alga). At least two blue-green
algae, Microcystis aeruginosa and Anabaena flos-aquae, are responsible for acute poisonings
of various animals.
Blue-green algae, along with certain bacteria, occur in alkaline hot springs, they can live at
maximum temperatures of 73-74ºC. Some Cyanobacteria of soil have been shown to remain
viable for 107 years and they have been recovered from house dusts.
A number of blue green algae grow in association with other organisms. Gleopacsa and
Nostoc are the phycobionts of lichens, while others like Nostoc and/or Anabaena occur within
the plant bodies of certain liverworts, water ferns, cycads and angiosperms where they can fix
nitrogen. Certain types are associated with Protozoa, where they have been called cyanelles.
In addition to poisoning animals, blue-green algae may be deleterious to human beings. For
example Lyngbya majuscula causes dermatitis.
6.1.2
Nitrogen Fixation
Cyanobacteria are the only algae known to be capable of transforming molecular nitrogen gas
into ammonia, which has can then be assimilated into amino acids, proteins, and other
nitrogen-containing cellular constituents. Three kinds of blue-green algae have been shown to
fix nitrogen: 1- the filamentous heterocystous species 2- certain unicellular (nonheterocystous
filamentous species, 3- certain nonheterocystous filamentous species, Plectonema boryanum,
although only under microaerophilic conditions. The nitrogen-fixing enzyme complex
nitrogenase is oxygen-sensitive, so that the highest rate of nitrogen fixation occurs under
reduced oxygen tensions. There is evidence that heterocysts reduce the elemental nitrogen and
transfer it to the adjacent vegetative cells. Experiment shows that Phycocyanin which is a
nitrogen reserve, declines in nitrogen-starved cultures. Under aerobic conditions, phycocyanin
developed in the vegetative cells next to the heterocycts. It reappears, under anaerobic
conditions, in the all the vegetative cells. Experiments show the sensitivity of nitrogenase to
oxygen and indicate that less oxygen apparently is present in the heterocysts than in the
vegetative cells.
It has been hypothesized that the sheaths of Gleocapsa, a unicellular blue-green alga that fixes
nitrogen, may somehow affect microaerophilic conditions in the cells that permit nitrogenase
activity.
The nitrogen-fixing capacity of blue-green algae has been made use of in the cultivation of
rice in which their growth is encouraged in the rice paddies.
6.1.3
Protoplast
The photosynthetic lamellae or thylakoids of blue-green algae, unlike those of other
chlorophyllose plants, are not enclosed in membrane-bounded groups to form chloroplasts.
Instead, they lie free in the cytoplasm. The thylakoids are the site of chlorophyll a, and the
accessory pigments also occur on their surfaces in the form of small particles, the
phycobilisomes. The accessory pigments are c-phycocyanin, c-allophycacyanin, and cphycoertytrin, the two former blue and the latter red.
Photosynthetic storage product of cyanobacteria is cyanophycean starch = cyanophycin
(also known as cyanophytan starch or glycogen).
Figure 6.3 An akinete (arrowhead) in Anabaena.
Figure 6.2 Heterocysts (arrows) in Anabaena, illustrating some
of the variation in heterocycsts appearance that occurs
among taxa. Note the conspicuous mucilaginous
sheath (arrowhead)
6.1.4
Motility
Many filamentous blue-green algae are not enclosed in firm sheaths; the hormogonia of those
that are, and some unicellular species, undergo movement when in contact with the substrate.
This movement, accomplished without evident organs of locomotion, is called gliding
movement and occurs also in some filamentous bacteria. It is thought that the oscillation of
certain trichomes like those of species of Oscillatoria is related to these waves of propulsion
of the superficial fibrils.
6.1.5
Form
The cyanobacteria contain unicellular, colonial, and filamentous species. A filament is
composed of a chain of cells, the trichome, and the enveloping stealth, if one is present. The
term trichome (meaning “hair”) is used as a synonym for an unsheathed individual filament.
The term hormogonium is applied to a short filament that results from break up of longer
filaments and serves as a means of vegetative reproduction.
6.1.6
Reproduction
The biological species concept cannot be used with cyanobacteria because sexual fusion of
gametes completely absent from these prokaryotes. In the unicellular blue-green algae,
reproduction is effected by cell division. In cell division in most blue-green algae, the cell
35
becomes constricted in the median plane and the two inner wall layers grow centripetally until
a septum is formed.
Colonial and filamentous Cyanobacteria reproduce by fragmentation in which segments of the
organism become separated from the parent, glide or float away, and grow into new
individuals. Fragmented sections of trichomes, called hormogonia are motile. They arise by
separation of adjacent terminal walls in the trichome or by the death of certain cells that may
become biconcave separation discs or necridia.
6.1.7
Akinetes
The specialized cells known as akinetes are thought to function as resting cells that allow
cyanobacteria to survive adverse conditions. Akinetes are produced only by cyanobacteria
that are also capable of producing heterocysts. These two types of specialized cells share a
number of features that distinguish them from vegetative cells. Particular glycolipids and
polysaccharides occur in the cell walls of both heterocysts and akinetes, but not vegetative
cells. Also, photosystem II is inactivated in the akinetes of at least some cyanobacteria, as it
typically the case for heterocysts. The observations suggest that early stages in the
differentiation of akinetes and heterocysts may be under the control of similar genetic
elements. Akinetes are typically distinguished from heterocysts, however, by absence of
specializations associated with nitrogen-fixation and, often, by large size. In many cases the
akinete wall is distinctively ornamented and may be darkly pigmented.
An akinete develops from a vegetative cell that becomes enlarged and filled with food
reserves (cyanophycin and glycogen granules) and increases its wall externally by an
additional complex investment. After a period of dormancy, the akinete may germinate.
b
a
Figure 6.4 Tolypothrix. (a) Hormogonia. (b) Separation disk (arrowhead) adjacent to a heterocyst; this is where false branches
usually occur in this organism.
Some viruses attack blue-green algae; these have been designated phycoviruses or blue-green
algal viruses (BGA viruses). The virus lyses and destroys the host algal cells. There is some
evidence from filed and laboratory tests that phycoviruses like LPP-1 may be effective in
controlling unwanted blooms of blue-green algae in nature.
6.1.8
Cyanobacteria and the origin of an oxygen-rich atmosphere
It is though that at the time when cyanobacteria first appeared (3.5 billion years ago), the
earths atmosphere was rich in carbon dioxide (10-100 times present level) and that oxygen
was sparse (about 10-8 times that of present levels). Cyanobacterial photosynthesis would not
have been limited by the availability of carbon dioxide, but oxygen-requiring eukaryotes
would not have been to exist. Thus the cyanobacteria dominated earth’s biosphere for at least
one billion years and probably more. Oxygen derived from their photosynthesis gradually
accumulated in the atmosphere, eventually reaching modern levels, about 21%. The rise to
dominance of cyanobacteria—the earliest known oxygenic photosynthesizers—has been
described as the single most significant evolutionary event in the history of life on earth, for
without it, subsequent origin of eukaryotic life would have been impossible.
Cenozoic
Mesozoic
Multicellular forms
Paleozoic
free oxygen
600
eukaryotic cells
1000
Oxygen from photosynthesis
0
Oxygen accumulates in atmosphere
An oxygen-rich atmosphere made aerobic (oxygen-using) respiration possible. The use of
oxygen as an electron acceptor resulted in an 18-fold increase in respiration efficiency,
necessary for survival of most eukaryotes. An oxygen-rich atmosphere—poisonous to all
anaerobic (non-oxygen using) prokaryotes—also caused a radical change in community
dominance by favouring organisms possessing aerobic metabolism. Finally, an oxygen-rich
atmosphere was necessary for generation of the stratospheric ozone shield that protects life on
earth’s surface from the damaging effects of ultraviolet radiation. This allowed algae and
other organisms to colonize surface waters and the land surface, habitats previously rendered
sterile by UV.
autotrophs
(photosynthesis)
prokaryotic cells
Precambrian
heterotrophs
organic evolution
chemical evolution
formation of Earth
5000
mya
Figure 6.5 Diagram illustrating that atmospheric oxygen increase is correlated with the appearance and radiation of eukaryotes.
(mya=millions of years ago)
37
6.2
Division EUGLENOPHYTA
The name of Euglenophyta comes from genus Euglena which means; eu, good, true, in Greek
+ glene, eye, in Greek.
Euglenoids are generally found in environment where there is an abundance of decaying
matter. Such habitats may also include nearshore marine or brackish sand and mud flats
characterized by decaying seaweeds or organic contamination, farm ponds, dipteran larvae
hindguts, and the rectum of tadpoles. Sometimes euglenoids form alarming blood-red surface
blooms that, so far as is known, are not harmful. However, in nearshore marine waters large
populations of euglenoids have been observed to occur among blooms of potentially toxic
algal species.
Because of their association with increased level of dissolved organics, euglenoids have been
used as environmental indicators of such conditions.
Mobile cells usually have only a thin mucilage layer, while immobile cells lacking flagella
may be embedded in relatively thick layers of jelly to form scum on water or other surfaces
that is one cell layer thick. Such mucilage-embedded immobile stages of cells––that under
other conditions are mobile––occur in a number of algal groups and are known as palmella or
palmelloid stages (Figure 6.8)
Except when they are encysted or in a palmella phase, Euglenoids are flagellate, having two
or several flagella. When there are two, one may be nonemergent from the anterior
invagination which consists of a canal and a reservoir. Euglenoid flagella are rather coarse as
compared with those of Chlorophyta. They have the usual (9+2) fibrillar arrangement and in
addition a paraflagellar rod.
The cell covering of euglenoids is known as pellicle. The euglenoids are probably the earliest
divergent (most ancient) group of eukaryotic algae. Only about one third of the known genera
possess green-pigmented chloroplasts. A number of euglenoid genera are phagotrophic (i.e.
they feed upon organic particles) and consequently possess cellular organelles that are
specialised for capture and ingestion of prey, including bacteria and small algal cells. Some
euglenoid predators are indiscriminate feeders, while others specialize, feeding only upon
selected diatom, for instance.
Ultrastructural surveys of cell structure and mitosis of euglenoids revealed close relationship
to a group of flagellate protozoa known as the kinetoplastids. Subsequent molecular analysis
corroborated this relationship and strongly suggested that a kinetoplastid/euglenoid clade
originated quite early within eukaryotes. The kinetoplastids are a great important group
because they include parasitic trypanasomes. Leismania tropica causes Aleppo boil (Şark
çıbanı, halep çıbanı). They contaminate to human with an insect as a porter. Trypanasome
gambiense cause sleeping sickness in Africa. T. cruzi cause Chagas sickness in Latin
America.
Euglenoids are distinguished from kinetoplastids by two principal features. The first is the
producing reserve storage granules known as paramylon, that does not stain blue-black
iodine-iodide solution and is found in the cytoplasm of even colourless form. The second
distinguishing feature is a superficial pellicle composed of ribbon-like, interlocking
proteinaceous strips that wind helically around cells just beneath the plasma membrane,
giving cells are striated appearance.
6.2.1
Reproduction
Sexual reproduction does not occur in euglenoids with regularity, if at all. Asexual
reproduction is by longitudinal division, proceeding from apex to base, such that euglenoids
in the process of cytokinesis appear to be “two-headed”
In response to changing environmental conditions, euglenoids may form resting cysts. Cyts
formation involves loss of flagella, increase in the number of paramylon granules, swelling
and rounding of the cells, increase in the number of mucilage bodies.
Figure 6.6 Diagram illustrating typical features of Euglena,
which include the flask-shaped pocket (reservoir),
from which one of the two flagella emerges.
Adjacent the reservoir are the eyespot and
contractile vacuole. Also typically visible with the
light microscope are paramylon granules, plastids,
and the nucleus with nucleolus and relatively large
chromosomes. (b) TEM view of longitudinally
sectioned Euglena cell. Note eyespot (ES),
plastids (P) with pyrenoids (Py) and Nucleus (N).
Figure 6.7 Dividing Euglena cell Figure 6.8 This is the palmelloid stage of development where the Euglena rounds up into a
with characteristic twoball discarding its flagellum. They will stay in this stage until their environment
improves.
headed
appearance.
Note also the large
number of paramylon
granules.
39
6.2.2
Euglenoid ecology
There are no truly planktonic euglenoid species. They are fundamentally occupants of
interfaces, such as the air-water and sediment-water boundaries. In such habitats euglenoids
can be infected by chytrids (primitive fungi) and consumed by herbivores including other
euglenoids, such as predacious Peranema. The euglenoid storage product, paramylon, is
comparatively indigestible; paramylon granules have been observed to pass through the gut of
herbivores unharmed. In order to digest euglenoid storage products, herbivores require a gut
enzyme, laminarase that can degrade paramylon.
Certain euglenoids are known for tolerating extreme conditions. Some seem able to migrate
into soils and persist there for long periods in a dormant state. Euglena mutabilis is able to
grow in extremely low pH waters, such as streams draining coal mines and the acidic, metal
contaminated ponds. The optimal pH for growth of this species is 3.0 but pH values lower
than 1.0 can be tolerated. Euglenoids are also reported to be able to adapt to salinity increases
more quickly than can other algae.
6.3
Division CRYPTOPHYTA
Cryptomonads, their name literally meaning “hidden single cells”, are among the most
inconspicuous of the algae. Cryptomonads are relatively small 3-50 µm in length––members
of the phytoplankton; they are often most abundant in cold or deep waters; they are readily
eaten by a wide variety of planktonic herbivores; and natural collections are not easily
preserved. The cell tending to burst readily when subjected to environmental shock.
Cryptomonads are probably most appreciated by plankton ecologists who recognize their high
quality as food for zooplankton and algal evolutionary biologists who not that significant
cryptomonads ultrastructure and molecular biology in the study of secondary endosymbiosis.
Cryptomonads and euglenoids share a number of characteristics.
Sharing features of the euglenoids and cryptomonads;
1. They occur fresh and marine environment
2. B vitamin is required by all members of both groups.
3. Fundamentally biflagellate, with flagella emerging from an apical depression.
4. They are primarily unicells that can also occur as nonmotile, mucilage embedded
palmelloid stages and most forms of both groups are essentially naked.
5. They can produce thick-walled cysts that are able to survive adverse conditions, but
neither group has a good fossil record.
6. Plastids of both groups arose by secondary endosymbiosis.
7. Photosynthetic storage of both groups occurs as granules in the cytoplasm.
Such similarities do not indicate that cryptomonads and euglenoids are closely related. Strong
ultrastructural and molecular evidence links the cryptomonads with the Glaucophytes.
Photosynthetic storage material in cryptomonads is starch, which like that of plants and green
algae, (but unlike euglenoid paramylon), stains blue-black with an iodide-iodid solution.
a
b
Figure (a) Cryptomonas obovata (b) Cryptomonas ovata
6.3.1
Ecology
Cryptomonads are especially prominent in oligotrophic, temperate, and high-latitude waters
of lakes and oceans. They seem to be more important in cold waters both lakes and oceans.
They seem to be more important in cold waters, typically becoming abundant in winter and
early spring when they can begin growth under the ice. For example, cryptomonads may
dominate the spring phytoplankton bloom in the North Sea where they are believed to make
significant contributions to net primary productivity. Localized blooms of cryptomonads also
occur in Antarctic waters; the bloom is correlated with the influx of water from melting
glaciers. In perennially ice-covered Antarctic lakes, Chroomonas lacustris or a Cryptomonas
species may dominate the algal flora during the austral summer, contributing more than 70%
of the total phytoplankton biomass. Crytomonads seem to occur only rarely in ocean waters at
temperatures of 22ºC or higher, and they are absent from hot spring and hypersaline waters.
In oligtrophic freshwater lakes, cryptomonads typically form large populations in deep waters
(15-23 m) at the junction of surface oxic (oxygen-rich) and bottom anoxic (oxygen-poor)
zones, where light levels are much lower than in surface waters.
A significant ecological aspect of cryptomonads is their incorporation within cells of the
mixotrophic ciliate Myrionecta rubra. This protozoan can form dramatic, red colored blooms
in waters off the coast of Peru and Baja, typically upwelling conditions that bring additional
nutrients to surface waters. The photosynthetic pigments of the cryptomonad endosymbionts
impart a red coloration to the ciliate host.
Certain dinoflagellates, including Gymnodinium acidotum and Amphidinium wigrense, also
regularly contain portions of cryptomonad cells, particularly plastids. These dinoflagellates
possess phagotrophic capabilities and can thus harvest most or parts of crytomonads or other
cells. In some cases the cryptomonads possess nuclei, but in others, only the plastids persist
within the dinoflagellate cytoplasm.
41
Figure 6.9 Cross section through an unidentified
cryptomonad, viewed with TEM. Note the
peripheral plastid (P), pyrenoid (Py) and starch
(S), Golgi body (G).
6.4
Division HAPTOPHYTA
Haptophyta algae are primarily marine unicellular biflagellates that have had a major impact
on global biochemistry for at least 150 million years. They are probably the single modern
algal group that has the greatest long-term impact on carbon and sulfur cycling and hence,
global climate. Most haptophyta species produce external body scales composed primarily
calcium carbonate that are known as coccoliths. Sedimented coccoliths are the major
contributors to ocean floor limestone accumulation, and represent the largest long-term sink
of inorganic carbon on the earth. Deep-sea carbonate deposits cover about one half of the
world’s seafloor, an area that represents one third of the earth’s surface. Coccoliths contribute
about 25% of the total annual vertical transport of the deep ocean. In addition, the coccolithsproducing Emiliana huxleyi, are known for their formation of extensive ocean blooms with
concomitant production of large amounts of dimetylsulfide (DMS), a volatile sulfurcontaining molecule that increases acid rain. Coccoliths, which readily reflect light, and DMS,
which enhances cloud formation, contribute to increased albedo (reflectance of the earth’s
surface) and thus have a cooling influence on the climate.
Haptophyta are also important in terms of their biotic associations. Most haptophytes contain
golden or brown plastids, and are thus photosynthetic primary producers. However, many are
osmotrophic or phagotrophic; thus mixotrophy is common. Phagotrophy is particularly
prominent among forms that lack a cell covering formed of coccoliths, but which possess a
haptonema, a thread-like extension from the cell that is involved in prey capture, among other
functions. A haptonema occurs in many haptophytes, hence the name of the group, although a
number of taxa appear to have lost this structure.
climate
albedo latent
head
clouds
storms
CO2
acid rain
temperature
DMS
Emiliania
nutrients
CO2
carbonate
organic carbon
respiration
sediments
Figure 6.10 Blooms of Emiliana huxleyi can have important effects on the earth’s climate in a variety of ways, summarized here
in diagram form.
Chrysochromulina polylepis can produce toxic offshore marine blooms that cause death of
fish and invertebrates, while Prymnesium parvum causes similarly toxic blooms in brackish
waters. In 1989, a P. parvum bloom along the Norwegian coast caused a five-million-dollar
loss of salmon.
With the exception of the toxic bloom-formers, haptophyta algae, because of their small size,
fast growth rates, digestibility, and nutritional content, are considered to be high-quality foods
for marine zooplankton. Haptophyta actually reach their highest species diversity in extremely
low-nutrient, subtropical open-ocean waters, where a number of strange and beautiful forms
mysteriously occur in nearly dark ocean waters more than 200 m deep.
6.4.1
Fossil record
The haptophyte algae have one of the best fossil records among the algae, because of often
round or oval calcite coccoliths are readily preserved in sediments. Coccoliths (Gr. kokkos,
berry + lithos, rock) were named in 857 by T. H. Huxley, who observed them in samples of
deep-ocean sediments. Coccoliths first appear in the fossil record either as early as
carboniferous, or in the Late Triassic (about 220 million years ago), continuing to the present
time.
43
-
HCO3
2+
Ca
coccolith
CO2
CO2
CO2
CaCO3
CO2
Figure 6.11 A diagram of an Emiliania huxleyi cell, illustrating that bicarbonate is taken into the cell and used in calcification,
which then provides additional CO2 for photosynthesis.
The rise of coccolithophorids followed the most dramatic worldwide extinction episode in
earth’s history—the 250million year ago end-Permian event. A richly diverse marine
community experienced the loss of 85% of its species. The cause is though to have been
extensive volcanism with the release of large amounts of CO2, resulting in acid rain, and
cooling caused by atmospheric ash, though other causes are also possible.
The abundance of coccolith fossils peaked during the Late Cretaceous (63-95 million years
ago), when very extensive chalk deposits were laid down across much of northern Europe and
other sites around the world. In fact, the term Cretaceous refers to this chalk. Some
blackboard chalks that are derived from such deposits contain coccolith remains.
The impact of massive asteroid or comet off the Yucatan coast (the famous “K/T event”),
which is associated the demise of dinosaurs and ammonites, also apparently caused extinction
of 80% of the coccolithophorids species that had been present in the cretaceous. In contrast,
dinoflagellates and diatoms seem to have escaped similar drastic extinction effects.
Because coccolith are common, small, and exhibit low endemism (restriction of certain
species to particular locales), they are widely used as stratigraphic indicators to match rocks
of equivalent ages from different locales. About 1000 species of fossil coccolithophorids are
widely used as bioindicators in the oil industry.
6.4.2
Thallus type
The most primitive haptophytes are thought to be biflagellate unicells having a haptonema.
Derived forms are considered to include flagellates with a highly reduced haptonema or none
at all, as well as nonflagellate amoeboid, coccoid, palmelloid, colonial, or filamentous forms
that produce biflagellate reproductive cells. Coccolith production is regarded as a derived
feature. Thus haptophytes probably originated much earlier than is suggested by the first
appearance of coccoliths in the fossil record, but did not leave remains because earliest forms
lacked distinctive fossilizable parts.
The haptonema, if present, emerges from the cell apex, between the flagella. The haptonema
is about the same thickness as a flagellum and was mistaken for a flagellum until its structure
was elucidated with transmission electron microscopy. The length and bending behavior of
the haptonema seem to be correlated with phagotrophic behavior; species having a very long
haptonema are inclined toward phagotrophy, whereas those having a very short or no
haptonema are not.
(a)
(b)
(c)
(d)
Figure 6.12 A diagram of the feeding process of Chrysochromulina. In (a) and (b), particles adhere to the haptonema and are
translocated downward to a particle aggregating center. In (c), the aggregated, captured particles are moved to the
tepi of the haptonema. In (d), the aggregate is delivered to the cell surface (at the posterior end of the cell) through
bending of the haptonema. Here is taken into the cell.
High speed video methods revealed of the haptonema in phagotrophy. As the cell swims
forward, prey particles—such as bacterial cells—attach to the forward-projecting haptonema.
Edhesive properties are attributed to presence of sugar groups at the haptonemal surface.
Particles are moved downward to a point about 2 µm distal to the haptonemal base, known as
the particle aggregating center (PAC). Once formed, the PAC moves up to the haptonemal tip
6.5
Division DINOPHYTA (dinoflagellates)
Dinoflagellates probably rank first among the eukaryotic algae in terms of the current and
potential future significance of their biotic association, which may have large impacts on
carbon cycling and coastal fisheries production. Dinoflagellate endosymbionts are essential to
the formation and existence of coral reef ecosystems; they exhibit an amazing diversity of
nutritional types, including autotrophs, mixotrophs, phagotrophs, and parasites; and some are
notorious for the production of toxic red tides (harmful algal blooms). These species
reproduce in such great numbers that the water may appear golden or red, producing a "red
tide". When this happens many kinds of marine life suffer, for the dinoflagellates produce a
neurotoxin which affects muscle function in susceptible organisms. Humans may also be
affected by eating fish or shellfish containing the toxins. The resulting diseases include
ciguatera (from eating affected fish) and paralytic shellfish poisoning, or PSP (from eating
affected shellfish, such as clams, mussels, and oysters); they can be serious but are not usually
fatal.
The term dinoflagellate originates from the Greek word dineo, meaning “to whirl”. However,
there are several non flagellate amoeboid, coccoid, palmelloid, or filamentous forms.
Dinoflagellates are second only to diatoms as eukaryotic primary producers in coastal marine
waters. Though most of too large (2-200 µm) to be consumed by filter feeders, dinoflagellates
45
are readily eaten by large protozoa, rotifers, and planktivorous fish, for which they can be (if
not toxic) high-quality food.
They exhibit high levels of living and fossil biodiversity (more than 550 genera and 4000
species); and the internal complexity of their cells rivals that of ciliate and sarcodine protozoa.
Together with cell membrane, the dinoflagellates cell covering consists of a single layer of
several to many closely adjacent, flattened amphiesmal (thecal) vesicles; the entire array is
known as the amphiesma. In many species the thecal vesicles each contain a thecal plate
composed of cellulose; such species are said to be armored or thecate. In some species the
ampiesmal vesicles are not good developed, cells appear to be naked and are referred to as
unarmored or non-thecate. Soma dinoflagellates dinospores of the invertebrate symbiont
(Symbiodinium) are regarded as intermediate between the armored and unarmored condition.
About half of the known species lack plastids and are there fore obligatory heterotropnic.
Parasitic forms also occur within the cells or tissue of fish, invertebrates, and filamentous
algae.
a
b
Figure 6.13 Armored dinoflagellates (a) Ceratium hirudinella (b) Peridinium
6.5.1
Bioluminescence
There is evidence that the bioluminescence exhibited by marine dinoflagellates has a
defensive function. When the algal cell agitated, they produce blue-green light that results
from reaction of the substrate luciferin with the enzyme luciferase, as in fireflies and various
bacteria. In the case of dinoflagellates, bioluminescence appears to decrease copepod
predation. Two possible protective mechanisms have been suggested: a direct “startle” effect
on the herbivores themselves and a more indirect effect—increased predation upon copepods
that have fed upon glowing dinoflagellates and thus rendered more visible to their predators.
Bioluminescence occurs in approximately 30 photosynthetic dinoflagellates, including
Gonyaulax and some non-photosynthetic marine forms, such as Noctiluca (Figure 6.14)
luciferase
+ O2
luciferin
oxiluciferin
0,1-s blue light
Bioluminescent dinoflagellates possess spherical intracellular structure known as scintillons
or microsources. These are about 0,5 µm in diameter and are arrayed at the cell periphery.
They are derived from the Golgi apparatus and contain luciferin, luciferase oxidizes the
luciferin with molecular O2, causing a 0,1-s flash of blue light.
The number of scintillons in Gonyaulax polyedra decreases from 540 per cell in the night
phase to just 46 in day-phase cells, and the amount of bioluminescence is two orders at
magnitude grater in night-phase cells. There is a daily (circadian) rhythm in synthesis and
destruction of scintilloins, luciferin, and luciferase. This is viewed as an adaptation that
conserves energy, as bioluminescence would not be visible in the day time.
Figure 6.14 Noctiluca scintillans, commonly known as the seasparkle, is bioluminescent. They cause the lighting of the sea.
6.6
Division OCHROPHYTA
In the past covered in this division (Diatoms, Chrysophycea, Hhaeophycea) had been grouped
with haptophyta in the division Chrysophyta. We use newer phylum concept Ochrophyta
because it is defined in terms of flagellar ultrastructure and molecular data, and thus more
closely reflects modern concepts of evolutionary relationships than do older taxonomic
concepts. Brown seaweeds and golden-brown diatoms, as well as incredibly diverse array of
other algae, belong to a group that we have chosen to call the Ochrophyta, or more informally,
the ochrophytes. The name reflects the ocher (golden-brown) color of many algae in this
group.
The term heterokont is using for Ochrophyta. This means “different flagella.” Although other
groups of algae possess flagella that are also distinctively different from each other
(dinoflagellates, for example) the organisms known as heterokonts typically have two flagella
(or have reproductive cells with such flagella) that differ in unique ways: along, forwarddirected flagellum bears two rows of stiff, there-parted hairs and a shorter, smooth flagellum
that often (but not always) bears a basal granule that functions in light sensing.
47
6.6.1
Diatoms
In terms of evolutionary diversification, the diatoms have been wildly successful. Though
occurring only as single cells or chains of cells, with 285 genera encompassing 10,000-12,000
recognized species, diatom diversity is rivaled among the algae only by the green algae. Some
experts believe that many diatom species remain to described and that diatom species may
actually number in millions.
In terms of contributions to global primary productivity, diatoms are among the most
important aquatic photosynthesizers. They dominate the phytoplankton of cold, nutrient-rich
waters, such as upwelling areas of the oceans, and recently circulated lake waters.
Diatoms are commonly grouped into two or there major categories, primarily on the basis of
frustule features that can be readily observed in living cells as well as fossils. The centric
diatoms typically have discoid or cylindrical cells having radial symmetry in face of valve
view. A valve is the top or bottom of silica frustule. Incontrast, valves of pinnate (referring to
“feathery” patterns of ornamentation on the frustule) diatoms have more or less bilateral
symmetry.
a
b
Figure 6.15 A comparison of (a) Pennate diatoms, typified by bilateral symmetry, with (b) centric diatoms, which have radial
symmetry.
6.7
Division CHLOROPHYTA
General features of green algae

Green pigmented algae (occasionally colourless) with true pyrenoids and starch.

Form ranges from unicellular through colonial, coenobial, filamentous, thalloid to
Siphonaceous.

Chromatophores one or more, often complex, but discoid in the siphanoceous genera.

Flagellate stages possessing two (four) or rarely more flagella.

Asexual reproduction via zoospores, aplanaspores, autospores, akinetes, palmelloid
stages or fragmentation.

Sexual reproduction isogamous, anisogamous, or oogamous.

Mostly haploid vegetative plants and with well developed alteration of generations in
some genera.

Freshwater, terrestrial and marine, but certain groups confined to one or other habitat.

Some genera symbiotic with fungi, forming lichens, and other symbiotic with animals
6.7.1
Class: Charophycea
Charophycean green algae represent the lineage that is ancestry to the land plants. The land
plants are thought to have first appeared more than 470 million years ago-the age of the
earliest fossils that are accepted as land plant remains. Charophyceans have been associated
with the ancestry of land plants on the basis of ultrastructural, biochemical, and molecular
evidence. Molecular sequence evidence established a close relationship of charophyceans to
land-plant ancestry.
Charophyceans include the macroscopic charalean algae such as Chara (for which the group
is named) and Nitella, which can be very common in some freshwater environment.
Charophycean algae also include microspobic desmids and the well-known Spirogyra and
related filamentous algae, which are referred to as zygnamataleans (named for the genus
Zygnema).
Macroscopic Charophyceans have along fossil record. This record reveals that relatives of
modern charaleans were the dominant form of macrophytic vegetation in freshwaters for
some three hundred million years prior to the origin of flowering plants. They are much less
diverse today than in some earlier time periods, modern charaleans are widespread and locally
abundant.
Microscopic charophyceans such as Spirogyra are famous for their high level of species
diversity there are more than 3.000 described species, with new forms continuing to be
discovered.
6.7.2
Order: Charales
Modern charaleans algae are important both ecologically and evolutionarily. They are closely
related to the ancestry of land plants. They have a long fossil history, based primarily upon
calcified reproductive structures that provide useful information about the evolutionary
process and patterns of extinction.
(a)
(b)
Figure 6.16 (a) Chara. (b) Nitella
49
6.7.3
Killer algae in the Mediterranean Sea
Alien or "killer" green alga (Caulerpa taxifolia) has made its way to San Diego and Orange
County. A strain of this species has invaded the Mediterranean and has spread uncontrollably
since 1984. The algae has been referred to like "laying astro-turf across the ocean floor"—
displacing everything in its path. It threatens coastal marine life, including native seagrass,
invertebrates, fish, marine mammals, and sea birds.
The production of a deadly poison by species of Caulerpa, referred to as caulerpicin, has been
recognized in Hawaii and in the Philippines and is known to enter into marine food chains.
Since freshly collected plants of Caulerpa are eaten in salads in some areas of the Pacific, the
health hazard is obvious.
•The algae spreads by fragmentation, and even a small piece can form a new plant. It is
believed the algae are transported to different areas via boat anchors and fishing gear.
•It is capable of extremely rapid growth—about an inch a day.
•The algae can survive in various depths and temperatures, and grows on almost any
substrate; it is not free-floating.
The invasive strain of Caulerpa taxifolia was first discovered in the Mediterranean Sea in
1984. Immediate eradication was not attempted and, as a consequence, within a few years
government officials determined the infestation to be uncontrollable. Today, marine scientists
in the Mediterranean are largely resigned to monitoring the seaweed's continuous expansion
over thousands of acres of sea floor.
The invasion of Caulerpa taxifolia: Since its introduction of the Mediterranean Sea, this
anthropogene hybrid seaweed keeps still expanding at a rapid pace. From the main site of
colonization (Menton to Cap d'Ail) it spreaded westwards to the municipality of Eze-sur-Mer
(both sites of southern France) and even further. Here, the total affected area (places where
more than 100 colonies per hectare have developed) now represents about 1360 hectare in
shallow waters.
Invasive Capacity of Caulerpa taxifolia
Chronology of the spread in the Mediterranean:
Date
3
2
# of Sites in Hectares (10E m )
2
Med Waves Report, Spring 1997
Place of Location
1984
1 site at 1 m
Monaco Coast
1990
3 sites, covering 3 hectares
Same coast line
1991
30 hectares
Same coast line
1993
1327 hectares
French coast line
1994
427 hectares
Monaco coast line
1994
1500 hectares
French coast line
1995
427 hectares
Same coast line
1997
4600 hectares
1999
Mediterranean Sea
2
6000 hectares (60 km )
Mediterranean Sea
This exponential increase is not only the result of spreading over short distances through the
dissemination of cuttings near the original patches.
According to last studies on the Turkey coast of Mediterranean Sea C. taxifolia was not
found. But other Caulerpa species, C. rasemosa was found which not toxic like C. taxifolia.
C. rasemosa is also invasive species and expanding and cover sea bottom.
7
ECONOMIC ASPECTS
Algae play a small but important part in the direct economy of many countries.
Four major products are derived commercially from algae;
1. Agar
2. Carrageen
3. Alginic acid (alginates)
4. Diatomite
The first two products are extracted from marine Rhodophyta, the third from Phaeophyceae,
and the fourth from either marine or freshwater diatom deposits. Other direct uses are as food,
for man and cattle, and as organic or inorganic (lime) fertilizers.
It is impossible to assess the full economic importance of algal growth but even the most
conservative estimates contribute 50 per cent of global carbon fixation to the algae; in aquatic
habitats algae are part of the food chain leading to crustacean and fish, on agricultural land
they are an important constituent of the soil flora, and in water supply reservoirs, purification
plants and in sewage disposal plants, they play an important role in oxygenation and filtration.
7.1
Agar
Agar extracted from rhodophycean algae. It is used as a medium in the culture of bacteria,
fungi and algae and also in numerous industrial processes. The term ‘agar’ has been used in
various implications; originally the Malayan word ‘agar’ or ‘agar-agar’ was used for certain
East Indian edible Rhodophyceae of the genus Eucheuma and probably, by extension, for
other seaweeds. Alga is manufactured mainly from Gelidium, Gracillaria, Pterocladia,
Phyllophora. Last species found in Black Sea and Russia, Romania and Turkey use this
species for production of agar.
Fig. Phyllophora nervosa, a Red Algae found in Black Sea and using for agar production
Carrageen
51
This is extracted from Rhdophycean alga Chondrus and to a lesser extent from Gigartina.
Chondrus, growing in the interdital zone is very abundant in the Canada and is harvested
there, using wooden rakes. Most of the processing is done in the United States. In the
presence of potassium, these compounds gel and are used like alginates to stabilize emulsions
and suspend solids, etc., in the food, textile, pharmaceutical, leather and brewing industries.
7.2
Alginic acid (alginate)
These are extracted from Phaeophyta, e.g. from Laminaria, Ascophyllum, Macrocystis,
Ecklonia, Eisenia. The alginic acid occurs in the middle lamella and primary walls of these
algae, while cellulose is found in the secondary walls. Its structure is very similar to that of
cellulose and pectic acid.
The use of alginates in industry depends on the chemical and physical properties of the
compounds, e.g. they are non-toxic, highly viscous and readily form gels. Alginates using
following areas:










7.3
Food industry (filling creams)
Cosmetics (e.g. hand creams)
Textile industry (as printing pastes)
Rubber industry in latex production
As emulsifiers (e.g. in ice cream, synthetic cream, processed cheese, pharmaceutical
emulsions, polishes, emulsion paints)
As gelling agents in confectionary and meat jellies.
As dental impression powders
Ceramic industry (in glazes)
Paper industry (as surface films)
Food industry (as alginate films in the sausage case)
Diatomite
During Tertiary an Quaternary times, the production of diatoms has been so great in some
regions that large sedimentary deposits have been formed. The siliceous cell walls are
relatively insoluble and hence these sediments accumulated in marine and freshwater basins
and some are relatively uncontaminated by clay, etc. In theses areas the thick deposits are
scooped up with large earth-moving equipment and processed in a modern chemical
engineering plant. The natural deposit contains a high proportion of silica. When processed it
is chemically inert and is mainly used as a filtration aid, as a filler in paints, varnishes, and
paper products an in insulation materials, particularly those for use at high at high and low
temperatures.
It is particularly important in the sugar refining and brewing industries. In wine making,
diatomite added as a filter aid, sometimes at as many as four stages in production. It is also as
a filter in the production of antibiotics when the waste mycelium, etc., is removed. In many
industrial processes the recovery of chemicals and reclamation and recycling of water is aided
by the addition of diatomite. Alfred Nobel made use of diatomite as an absorbent for nitroglycerin in the manufacture of dynamite, but it has now been replaced by other substances.
Diatomaceous earth was used to make lightweight bricks in the building of the 32,6 m dome
of the Cathedral of St. Sophia in Istanbul in A.D. 532.
7.4
7.4.1
Other aspect of using algae
Fertilizer
In a small way algae are used as fertilizers on farmland close to the sea. The larger brown and
red algae are used as organic fertilizers; these are usually richer in potassium but poorer in
nitrogen and phosphorus than farm manure. The weed is usually applied direct and ploughed
in, but it also been processed into a seaweed meal for transport inland. A concentrated extract
of seaweeds is sold as liquid fertilizer.
7.4.2
Fodder
In maritema districts seaweeds have been used directly for animal fodder with beneficial
effects; this effects may be related to the high vitamin and micronutrient content. The time of
collection, drying, preparation, and the storage of the meal all affect the nutrient value,
particularly the vitamin content, which can be halved in Fucus meals stored for five months.
The ascorbic acid (vitamin C) content is at a maximum in early summer and a minimum in
mid-winter.
Many fish, both marine and freshwater, feed on planktonic or attached algae. Diatoms are
apparently easily digested by most fish, although the silica frustules are not utilized. Young
marine fish are also known to feed extensively on benthic microscopic algae particularly those
attached to sand grains.
7.4.3
Food
Only in the Far East have algae been regularly used for human food. In the pacific Islands the
raw algae, usually species of Rhodophyta, but also Chlorophyta and Phaeophyta, are chopped
and added to other dishes. Young stipes of Laminaria and the reproductive leaflets of Alaria
have also been eaten without much preparation in Europe and N. America. The most prolific
users of seaweeds are however the coastal population of china, Japan and o tropical Pacific
Islands, where numerous genera are used. The commonest are species of Porphyra and of
Laminaria.
The extensive experiments on mass algal culture show without doubt that if necessary, algae,
particularly Chlorella, could be grown and processed into food.
Deleterious effects
Under certain circumstances and in particular during periods of mass production, algae or
their toxic products may cause injury or even mortality amongst animals. In fish ponds and in
nature, mass growth of filamentous and mucilaginous species results in a physical smothering
and/or oxygen depletion leading to death of young fish fry. The most widespread harmful
affects are those caused by algal blooms.
In the oceans, species of Dinoflagellates often cause the red discoloration known as “red
tides,” while in freshwaters the blooms are usually due to Cyanobacteria, although some of
the most detrimental are caused by minute flagellates. Strong poisons have been extracted
from algae causing water blooms, and from shellfish feeding on the algae. It has been shown
that mussels can store large amounts of these toxins, and when eaten by man, these cause
paralytic shellfish poisoning.
In freshwaters the most common deleterious algae are species of Cyanobacteria (Microcystis,
Aphanizomenon, Anabaena, etc.) killing aquatic animals, farm animals and birds, especially
those which drink the surface waters where there is the greatest concentration of plankton
during an “algal bloom.”
53
8
BIOLOGICAL ASSESSMENT IN WATER POLLUTION.
The effect of pollution on rivers or standing waters can be measured chemically, since it
usually involves the addition of toxic substances or of organic wastes which on decomposition
deplete the oxygen supply. However, the deleterious effects are on the organisms and the
degree of pollution can often be measured most easily by a biological analysis, in which algae
are important indicators. Algae are sensitive to the degree of reducing or oxidizing activity in
the water. In the reducing zone, where oxygen is completely depleted, algae are subordinate to
bacteria, especially sulphur bacteria. However, even in this type of water (polysabrobic), a
few algae may survive, e.g. Oscillatoria chlorina, Spirulina jenneri, Euglena spp. and a few
other flagellates. In the next zone (mesosaprobic), oxygen is not completely depleted and
algae can grow; these zones succeed one another down a river from the source of pollution, or
spread out in concentric zones in ponds and lakes. Two subdivision of this zone are often used
and it is only the α-mesosaprobic zone which is polluted in the common sense of the word.
Here Oscillatoria spp., Nitzchia palea, Gomphonema parvulum appear and indicate the
improvement in the water. The β-mesosaprobic zone may be still polluted on a chemical
basis, but so far as the algae are concerned, it supports a rich flora comparable to that of many
eutrophic waters. Further degreesof purity are found in oligosaprobic waters (i.e. in the upper
reaches of streams or in oligotrophic lakes) and in katharobic waters where organic matter es
at a minimum (e.g. in spring waters).
Increasing organic matter
Katharobic
Oligsaprobic
β-mesosaprobic
α-mesosaprobic
Polysaprobic
Saprobic zones
In water polluted by toxic chemicals, even the bacterial flora may be killed and no breakdown
of the effluents is possible. Short-term pollution of this type may be difficult to detect
chemically since the effluent may pass away rapidly but biological assessment will reveal the
extent to which the algal flora has suffered.