Download 321-12-taxa-Diatoms2005

GEOL 3213
MICROPALEONTOLOGY
Diatoms:
Introduction & Classification
Photosynthetic algae
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Phylum – Bacillariophyta (diatoms)
*Phylum – Chrysophyta (chrysophytes)
Phylum – Haptophyta (coccoliths)
Phylum – Phaeophyta (brown algae)
Phylum – Chlorophyta (green algae)
Phylum- Rhodophyta (red algae)
etc.
*Diatoms and coccoliths are grouped together with
the chrysophyta (includes silicoflagellates) by
some workers.
Other
“Algae”
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Diatoms – Biology & Ecology
Unicellular &/or colonial organisms
Eukaryotic
Lack flagella
Asexual and sexual reproduction
May be single celled or in chains
Photosynthetic, productive even in cold nutrient-rich water (Antarctic, etc.)
Base of the food chain = “Grass of the sea” (Account for up to 25% total world
primary food production by phytoplankton. Some species harvested for food
for shellfish industry.)
• Planktic and benthic forms
Seafloor siliceous ooze
composed of diatoms and
radiolaria
Diatoms – Biology & Ecology
• Can move on & within the sediment with mucus
streamers associated with a groove called the raphe
• Can live heterotrophically in the dark
• Occurrences:
– Freshwater (lacustrine, swamp, marsh, riverine)
– Marine (shoreline environments to the deep sea)
– Other:
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Damp terrestrial
Hot springs
Hypersaline lakes
Melt-water pools on icebergs
• Diversity of benthic forms is high worldwide
Diatom Classification
• Diatoms are the “golden brown” algae
• Some researchers classify them in the Phylum
Bacillariophyta
• Other workers put them, with the coccolithophores &
silicoflagellates, in the Phylum Chrysophyta
• Frustrule (porous valves) shapes vary greatly, so there is
no simple summary of morphology
• Two major subdivisions are recognized:
– Centrales (centric) = circular, oblong, hemicircular, triangular,
or quadrangular, with surface features arranged around a
central point – radially symmetrical
– Pennales (pennate) = elongate with major features at right
angles to the median line (long axis). (These are further
subdivided into 7 subgroups.) - bilaterally symmetrical
• Range:
Diatom Skeletons
– Jurassic(?) marine, Mid-Cretaceous to Recent
– Oldest nonmarine forms are Eocene
• Skeleton called a frustrule
– Overlapping bivalves
• Box = hypotheca
• Lid = epitheca
• Overlapping sides = girdle
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Porous (called punctae); striae & costae
Raphe = groove = for locomotion?
Opaline
Marine dominantly centric forms (Cretaceous to Recent)
Nonmarine dominantly pennate forms (Paleocene to Recent)
As small as 5 um and up to 500 or more um
Account for 70-90% siliceous particles suspended in oceanic water
Siliceous skeleton resistant to solution in deep sea sediments
Diagenetic solution & reprecipitation leads to chert formation
Sediments: oozes, diatomaceous earth, diatomite
HOW DIATOMS REPRODUCE
• Reproduction mainly asexual – occurs during mitosis. Some sexual
reproduction with meiosis (when population sizes very small)
• Alternation of sexual and asexual reproduction
• Figure below: Girdle views of diatom valves through several reproductive
phases. Note the progressive decrease in size of some forms.
Diatom structure
• Frustule made of polymerized opaline silica
joined in two overlapping halves. Two halves fit
together like Petri dish – elaborate “glass houses”
• “Raphe” - Tiny slit that runs along cells – thought
that tiny microfibrils extrude from this to enable
locomotion
• Pennate form – better movers – more common in
freshwater
• Centric form – more common in marine.
Diatom Morphology
• Striae = line
of punctae
• Costae =
raised ridge
parallel to
striae
Centrales
Examples of Centrales
Pennales
Examples of Pennales
Diatom Diversity Through Time
• Centric forms
– Cretaceous to Recent
– Dominate the plankton
• Pennate forms
– Paleocene to Recent
– Dominate the benthos
Diatoms Uses
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Applications of diatom studies
– Used a lot by Quaternary geologists
– Age-dating and correlation
• Many short-ranged species
• Especially for the Tertiary
– Paleoenvironmental studies
– O18/O16 ratios used for paleotemperature studies
– Used to detect polluted water because of environmental sensitivity, e. g., to nitrate and
phosphate nutrient enrichments
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Natural absorbent: Diatoms from marine & freshwater deposits are mined because
– Highly porous
– Low density
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Used to make dynamite:
– Without its adsorbent character, Nobel's invention would not have been possible
– Absorbing nitro-glycerin into diatomite made possible it's
• Transport
• Safe use
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Other major industrial uses are:
– Filtration
• Water purification
• Wine & beer industry use diatomite during filtration processes
– Abrasive (fine)
• Silver polish (why?)
But they are not all good and beautiful….
• Big contibutors to 'natural' occurrences of toxic
marine conditions.
– Eutrophication:
• Along coasts - Some diatom blooms have caused mass
pollution, oxygen depletion, exphixiation, starvation.
– Marine biotoxin ('domoic acid’) – Some diatom
species that produce it are members of the planktonic
genera Pseudonitzschia & Peragallo
• Domoic acid is a naturally occurring amino acid and is a
glutamate analogue that strongly binds to the glutamate
receptors in the brain where it causes nerve cells to transmit
impulses continuously until the cells die.
End of File
• Which of these diatoms are
pennate diatoms & which are
centric diatoms?
End of File
Examine the slides with marine diatoms
Name: ______________
Diatom Lab Exercise
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2. Examine the slides with freshwater diatoms
Reason(s)
3. Determine which of the unknowns is from a freshwater deposit
and which is from a marine deposit. State your reasons:
Unknown Marine? Nonmarine?
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2.
Heterokonts = “different flagella”
1) Tinsel - Long pleuronematic flagellum,
directed forward during swimming
– Lining pleuronematic flagellum are two rows
of special, stiff hairs, called mastigonemes (or
flimmers). The mastigonemes are composed
of glycoprotein and are synthesized in the
cisternae of the endoplasmic reticulum.
2) Whiplash - a shorter smooth flagellum that
points backwards along the cell.
The smooth, backwardly directed flagellum
bears a swelling near its base, which fits
against the concave eyespot. The eyespot lies
at the anterior of the cell, enclosed within the
chloroplast, and consists of a single layer of
globules containing reddish-orange pigment.
The eyespot and flagellar swelling together
form the photoreceptor apparatus, which is the
light-perceiving organelle of the cell.
Molecular studies
• 1) fungus like heterokonts – diverged early
• 2) pigmented heterokonts derived from a single,
common ancestor
• 3) early separation of the pigmented forms into two
clades: diatoms vs the rest.
• 3) green algae – clear ancestor of plants. Plants
paraphyletic to protists.
Life cycles
• Zygotic meiosis – fungi and some algae
– Dominant phase haploidy, transient zygotes divide
meiotically and form new haploids.
• Gametic meiosis – animals, water molds and
some green and brown algae
– Zygote produces haploid gametes that fuse and
restore diploidy. Gametes do not grow.
• Sporic meiosis (alternation of generations) –
plants, many algae and some others
• Meiosis produces spores which can divide mitotically to
create multicellular haploid organism. These
gametophytic cells can fuse - sporophyte