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PHYTOPLANKTON
Submitted By
Md Juwel Hasan
Md Mubarak Hossain
Faculty of Fisheries.
Bangabandhu Sheikh Mujibur Rahman Agricultural University
Gazipur-1706, Bangladesh
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PHYTOPLANKTON
INTRODUCTION
Phytoplankton, also known as microalgae, are similar to terrestrial plants in that they contain
chlorophyll and require sunlight in order to live and grow. Most phytoplankton are buoyant
and float in the upper part of the ocean, where sunlight penetrates the water. Phytoplankton
also require inorganic nutrients such as nitrates, phosphates, and sulfur which they convert
into proteins, fats, and carbohydrates. In a balanced ecosystem, phytoplankton provide food
for a wide range of sea creatures including whales, shrimp, snails, and jellyfish. When too
many nutrients are available, phytoplankton may grow out of control and form harmful algal
blooms (HABs). These blooms can produce Most phytoplankton are too small to be
individually seen with the unaided eye. However, when present in high enough numbers,
some varieties may be noticeable as colored patches on the water surface due to the presence
of chlorophyll within
their
cells
and
accessory
pigments
(such
as phycobiliproteins orxanthophylls) in some species.
extremely toxic compounds that have harmful effects on fish, shellfish, mammals, birds, and
even people.
Fig: 01 Phytoplankton
The two main classes of phytoplankton are dinoflagellates and diatoms. Dinoflagellates use a
whip-like tail, or flagella, to move through the water and their bodies are covered with
complex shells. Diatoms also have shells, but they are made of a different substance and their
structure is rigid and made of interlocking parts. Diatoms do not rely on flagella to move
through the water and instead rely on ocean currents to travel through the water.
IMPORTANCE OF PHYTOPLANKTON
The food web
Phytoplankton are the foundation of the aquatic food web, the primary producers, feeding
everything from microscopic, animal-like zooplankton to multi-ton whales. Small fish and
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invertebrates also graze on the plant-like organisms, and then those smaller animals are eaten
by bigger ones. Phytoplankton can also be the harbingers of death or disease. Certain species
of phytoplankton produce powerful biotoxins, making them responsible for so-called ―red
tides,‖ or harmful algal blooms. These toxic blooms can kill marine life and people who eat
contaminated seafood.
Fig 02: Dead fishes
Dead fish washed onto a beach at Padre Island, Texas, in October 2009, following a red tide
(harmful algal bloom).)
Phytoplankton cause mass mortality in other ways. In the aftermath of a massive bloom, dead
phytoplankton sink to the ocean or lake floor. The bacteria that decompose the phytoplankton
deplete the oxygen in the water, suffocating animal life; the result is a dead zone.
Climate and the carbon cycle
Through photosynthesis, phytoplankton consume carbon dioxide on a scale equivalent to
forests and other land plants. Some of this carbon is carried to the deep ocean when
phytoplankton die, and some is transferred to different layers of the ocean as phytoplankton
are eaten by other creatures, which themselves reproduce, generate waste, and die.
Fig 03: Climate and the Carbon Cycle
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Phytoplankton are responsible for most of the transfer of carbon dioxide from the
atmosphere to the ocean. Carbon dioxide is consumed during photosynthesis, and the carbon
is incorporated in the phytoplankton, just as carbon is stored in the wood and leaves of a tree.
Most of the carbon is returned to near-surface waters when phytoplankton are eaten or
decompose, but some falls into the ocean depths
Worldwide, this ―biological carbon pump‖ transfers about 10 gigatonnes of carbon from the
atmosphere to the deep ocean each year. Even small changes in the growth of phytoplankton
may affect atmospheric carbon dioxide concentrations, which would feed back to global
surface temperatures.
Economic importance
Phytoplankton's role in the global ecosystem has made them a target for controlling carbondioxide levels in the earth's atmosphere. Companies such as Climos and Planktos have
invested in phytoplankton as a means of reducing carbon-dioxide emissions. They are
investigating fertilizing phytoplankton communities with iron, a vital nutrient, to promote
their growth. As political and economic pressures to provide carbon-dioxide emissions offsets
increases, the potential profit of companies like these increases.
OBJECTIVES
After this assignment we will be able to know the different type of phytoplankton, their
community, their habitat and importance of them.
PHYTOPLANKTON BIOLOGY
There are two major groups of phytoplankton—
(1) fast-growing diatoms, which have no means to propel themselves
through the water, and
(2)flagellates and dinoflagellates, which can migrate vertically in the water column in
response to light. Each group exhibits a tremendous variety of cell shapes, many with
intricate designs and ornamentations.
All species of phytoplankton are at the mercy of oceanic currents for transport to areas that
are suitable for their survival and growth. Thus, physical processes can play a significant role
in determining the distribution of phytoplankton species. Rapid cell division and population
growth in phytoplankton can produce millions of cells per liter of seawater, resulting in
visible blooms or ―red tides.‖ It remains difficult to avoid the harmful effects associated with
blooms of these toxic species because phytoplankton ecology is not fully understood.
―red tide‖ is misleading, because phytoplankton blooms frequently are other colors, such as
brown, green, and yellow, and are in any case not a tidal phenomenon.
Nearly all phytoplankton blooms along the California coast and within the Gulf of the
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Farallones involve nontoxigenic species. Conversely, most incidents of paralytic shellfish
poisoning (PSP) in humans caused by eating shellfish.
Phytoplankton vary widely in physical and chemical requirements for population growth.
Diatoms and dinoflagellates also differ significantly with respect to motility, cell-wall
composition and ornamentation, and nutritional and reproductive strategies.
Diatoms have cell walls, called frustules, made of silica (the same material in glass and opal).
In contrast, dinoflagellates can have a rigid cell wall, called a theca, made of cellulose plates,
or they can have a nonrigid cell membrane (no theca).
These two forms of dinoflagellate structures gave rise to the terms ―armored‖ and
―unarmored‖ (or ―naked‖) dinoflagellates. Diatoms and dinoflagellates can be highly
ornamented, which aids in species identification. Cellsurface designs on some diatoms may
help focus light on chloroplasts, allowing survival at greater depths where light intensity is
very low. Long spines, cell shape, and the formation of chains and colonies make diatoms
more difficult for predators to grasp or bite and also assist in flotation. Some dinoflagellates
form chains, whereas others have protuberances that look like wings, crowns, or horns, for
similar reasons.
ECOLOGY OF PHYTOPLANKTON
These are primarily macronutrients such as nitrate, phosphate or silicic acid, whose
availability is governed by the balance between the so-called biological
pump and upwelling of deep, nutrient-rich waters. This has led to some scientists
advocating iron fertilization as a means to counteract the accumulation of human-produced
carbon dioxide (CO2) in the atmosphere Large-scale experiments have added iron (usually as
salts such as iron sulphate) to the oceans to promote phytoplankton growth and
draw atmospheric CO2 into the ocean. However, controversy about manipulating the
ecosystem and the efficiency of iron fertilization has slowed such experiments.
Phytoplankton depend on other substances to survive as well. In particular, Vitamin B is
crucial. Areas in the ocean have been identified as having a major lack of Vitamin B, and
correspondingly, phytoplankton.
While almost all phytoplankton species are obligate photoautotrophs, there are some that
are mixotrophic and other, non-pigmented species that are actually heterotrophic (the latter
are often viewed as zooplankton). Of these, the best known are dinoflagellate genera such
as Noctiluca and Dinophysis, that obtain organic carbon by ingesting other organisms
or detrital material.
There are about 5,000 known species of marine phytoplankton. There is uncertainty in how
such diversity has evolved in an environment where competition for only a few resources
would suggest limited potential for niche differentiation.
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GROWTH STRATEGY
In the early twentieth century, Alfred C. Redfield found the similarity of the phytoplankton’s
elemental composition to the major dissolved nutrients in the deep ocean However, Redfield
ratio is not a universal value and it may diverge due to the changes in exogenous nutrient
delivery
and
microbial
metabolisms
in
the
ocean,
such
as nitrogen
fixation, denitrification and anammox.
The dynamic stoichiometry shown in unicellular algae reflects their capability to stockpile
nutrients in internal pool, shift between enzymes with various nutrient requirements and alter
osmolyte composition. Different cellular components have their own unique stoichiometry
characteristics,for instance, resource (light or nutrients) acquisition machinery such as
proteins and chlorophyll contain high concentration of nitrogen but low in phosphorus.
Meanwhile, growth machinery such as ribosomal RNA contains high nitrogen and
phosphorus concentration.
Survivalist phytoplankton has high ratio of N:P (>30) and contains numerous resourceacquisition machinery to sustain growth under scarce resources. Bloomer phytoplankton has
low N:P ratio (<10), contains high proportion of growth machinery and adapted to
exponential growth. Generalist phytoplankton has similar N:P to Redfield ratio and contain
relatively equal resource-acquisition and growth machinery.
ENVIRONMENTAL CONTROVERSY
Estimates of phytoplankton change in the oceans have been highly variable. One global ocean
primary productivity study found a net increase in phytoplankton, as judged from measured
chlorophyll, when comparing observations in 1998–2002 to those conducted during a prior
mission in 1979–1986. However, using the same database of measurements, other studies
have found that both chlorophyll and primary production had declined over this same time
interval. The airborne fraction of CO2 from human emissions, the percentage neither
sequestered by photosynthetic life on land and sea nor absorbed in the oceans abiotically, has
been almost constant over the past century, and that suggests a moderate upper limit on how
much a component of the carbon cycle as large as phytoplankton may have declined, if such
declined in recent decades.In the example of the northeast Atlantic, a case where chlorophyll
measurements extend particularly far back, the location of the Continuous Plankton Recorder
(CPR) survey. there was net increase over a 1948 to 2002 period examined.During 1998–
2005, global ocean net primary productivity rose during 1998 followed by primarily decline
during the rest of that period, although still slightly higher at its end than at its start.Using six
different climate model simulations, a large multi-university study of ocean ecosystems
predicts.
"a global increase in primary production of 0.7% at the low end to 8.1% at the high end,"
although with "very large regional differences" including "a contraction of the highly
productive marginal sea ice.
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Fig 04: Phytoplankton in sea
"However, a more recent multi-model study estimated that primary production will decline
by 2-20% by 2100 A.D.Despite substantial variation in both the magnitude and spatial pattern
of change, the majority of published studies predict that phytoplankton biomass and/or
primary production will decline over the next century
PHYTOPLANKTON IN AQUACULTURE
Phytoplankton are a key food item in both aquaculture and mariculture. Both utilize
phytoplankton as food for the animals being farmed. In mariculture, the phytoplankton is
naturally occurring and is introduced into enclosures with the normal circulation of seawater.
In aquaculture, phytoplankton must be obtained and introduced directly. The plankton can
either be collected from a body of water or cultured, though the former method is seldom
used. Phytoplankton is used as a foodstock for the production of rotifers, which are in turn
used to feed other organisms. Phytoplankton is also used to feed many varieties of
aquacultured molluscs, including pearl oysters and giant clams.
The production of phytoplankton under artificial conditions is itself a form of aquaculture.
Phytoplankton is cultured for a variety of purposes, including foodstock for other
aquacultured organisms,a nutritional supplement for captive invertebrates in aquaria. Culture
sizes range from small-scale laboratory cultures of less than 1L to several tens of thousands
of liters for commercial aquaculture.Regardless of the size of the culture, certain conditions
must be provided for efficient growth of plankton. The majority of cultured plankton is
marine, and seawater of a specific gravity of 1.010 to 1.026 may be used as a culture
medium. This water must be sterilized, usually by either high temperatures in an autoclave or
by exposure to ultraviolet radiation, to prevent biological contamination of the culture.
Various fertilizers are added to the culture medium to facilitate the growth of plankton. A
culture must be aerated or agitated in some way to keep plankton suspended, as well as to
provide dissolved carbon dioxide for photosynthesis. In addition to constant aeration, most
cultures are manually mixed or stirred on a regular basis. Light must be provided for the
growth of phytoplankton. The colour temperature of illumination should be approximately
6,500 K, but values from 4,000 K to upwards of 20,000 K have been used successfully. The
duration of light exposure should be approximately 16 hours daily; this is the most efficient
artificial day length.
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LONG-TERM CHANGES IN PHYTOPLANKTON
Productivity
Because phytoplankton are so crucial to ocean biology and climate, any change in their
productivity could have a significant influence on biodiversity, fisheries and the human food
supply, and the pace of global warming.
Many models of ocean chemistry and biology predict that as the ocean surface warms in
response to increasing atmospheric greenhouse gases, phytoplankton productivity will
decline. Productivity is expected to drop because as the surface waters warm, the water
column becomes increasingly stratified; there is less vertical mixing to recycle nutrients from
deep waters back to the surface.
About 70% of the ocean is permanently stratified into layers that don’t mix well. Between
late 1997 and mid-2008, satellites observed that warmer-than-average temperatures (red line)
led to below-average chlorophyll concentrations (blue line) in these areas. (Graph adapted
from Behrenfeld et al. 2009 by Robert Simmon.)
Over the past decade, scientists have begun looking for this trend in satellite observations,
and early studies suggest there has been a small decrease in global phytoplankton
productivity. For example, ocean scientists documented an increase in the area of subtropical
ocean gyres—the least productive ocean areas—over the past decade. These low-nutrient
―marine deserts‖ appear to be expanding due to rising ocean surface temperatures.
Species composition
Hundreds of thousands of species of phytoplankton live in Earth's oceans, each adapted
to particular water conditions. Changes in water clarity, nutrient content, and salinity
change the species that live in a given place.
Because larger plankton require more nutrients, they have a greater need for the
vertical mixing of the water column that restocks depleted nutrients. As the ocean has
warmed since the 1950s, it has become increasingly stratified, which cuts off nutrient
recycling.
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Continued warming due to the build up of carbon dioxide is predicted to reduce the
amounts of larger phytoplankton such as diatoms), compared to smaller types, like
cyanobacteria. Shifts in the relative abundance of larger versus smaller species of
phytoplankton have been observed already in places around the world, but whether it
will change overall productivity remains uncertain.
PHOTOSYNTHESIS
Phytoplankton biomass in the world's oceans amounts to only ∽1-2% of the total global
plant carbon, yet these organisms fix between 30 and 50 billion metric tons of carbon
annually, which is about 40% of the total. On geological time scales there is profound
evidence of the importance of phytoplankton photosynthesis in biogeochemical cycles. It
is generally assumed that present phytoplankton productivity is in a quasi steady-state
(on the time scale of decades). However, in a global context, the stability of oceanic
photosynthetic processes is dependent on the physical circulation of the upper ocean
and is therefore strongly influenced by the atmosphere.. These latter two parameters
are keys to determining the intensity, and spatial and temporal distributions of
phytoplankton blooms. Atmospheric radiation budgets are not in steady-state. Driven
largely by anthropogenic activities in the 20th century, increased levels of IR- absorbing
gases such as CO2, CH4 and CFC's and NOx will potentially increase atmospheric
temperatures on a global scale. The atmospheric radiation budget can affect
phytoplankton photosynthesis directly and indirectly. Increased temperature
differences between the continents and oceans have been implicated in higher wind
stresses at the ocean margins. Increased wind speeds can lead to higher nutrient fluxes.
Throughout most of the central oceans, nitrate concentrations are sub-micromolar and
there is strong evidence that the quantum efficiency of Photosystem II is impaired by
nutrient stress. Higher nutrient fluxes would lead to both an increase in phytoplankton
biomass and higher biomass-specific rates of carbon fixation. However, in the center of
the ocean gyres, increased radiative heating could reduce the vertical flux of nutrients to
the euphotic zone, and hence lead to a reduction in phytoplankton carbon fixation.
Increased desertification in terrestrial ecosystems can lead to increased aeolean loadings
of essential micronutrients, such as iron.
An increased flux of aeolean micronutrients could fertilize nutrient-replete areas of the
open ocean with limiting trace elements, thereby stimulating photosynthetic rates. The
factors which limit phytoplankton biomass and photosynthesis are discussed and
examined with regard to potential changes in the Earth climate system which can lead
the oceans away from steady-state. While it is difficult to confidently deduce changes in
either phytoplankton biomass or photosynthetic rates on decadal time scales, time-series
analysis of ocean transparency data suggest long-term trends have occurred in the
North Pacific Ocean in the 20th century. However, calculations of net carbon uptake by
the oceans resulting from phytoplankton photosynthesis suggest that without a supply
of nutrients external to the ocean, carbon fixation in the open ocean is not presently a
significant sink for excess atmospheric CO2.
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Both groups commonly reproduce by simple cell division. Some species of diatoms and
dinoflagellates are known to produce resting stages. Resting spores in diatoms, and cysts
in
dinoflagellates, allow species to survive in unfavorable conditions. Some diatoms form
specialized sexual-reproductive structures called auxospores that look like greatly
enlarged versions of normal vegetative cells. Dinoflagellates have motile sexual phases
that may become cysts or normal vegetative cells, depending on prevailing conditions.
124 Although all species of dinoflagellates and diatoms share certain basic requirements
for growth (light, carbon dioxide, nutrients, trace elements, habitable temperature and
salinity), they can differ considerably in their optimal requirements for these factors.
Nutritionally, diatoms rely solely on photosynthesis as a source of energy; they cannot
survive if they are transported below the photic zone. Dinoflagellates, in contrast, have
several survival strategies, ranging from photosynthesis to predation and parasitism.
SEASONAL SUCCESSION
Certain species become dominant at a certain period of time, after this time they
disappear and another group comes to take place which is called succession. This
succession plankton when related to season is called seasonal succession. In different
time of a year there are abundance of different phytoplankton in a system as follow-
Fig 05: Seasonal succession
BLOOMS, RED TIDES, AND TOXICITY
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Phytoplankton blooms in general, and toxic blooms in particular, have been increasing
in frequency and distribution worldwide since the 1980’s. Although the reasons for this
apparent increase are unclear, several have been suggested:
(1) increased nutrient input to coastal oceans from human activities,
(2) large-scale climactic changes (for example, global warming),
(3) transport of toxigenic species in ship ballast water,
(4) increased use of coastal resources for 125 shellfish harvesting and aquaculture, and
(5) increased surveillance by government health agencies and researchers.
The commonly used term “red tide” is quite misleading because phytoplankton blooms
frequently are other colors (brown, green, even yellow) and are not a tidal phenomenon.
Although diatoms are more numerous than dinoflagellates in terms of number of
species, the
dinoflagellates are associated with worldwide occurrences of red tides.
A unique characteristic of some red tides is the phenomenon of bioluminescence. Light
produced by some species of dinoflagellates (Noctiluca scintillans, Lingulodinium
polyedra) can actually illuminate the waves and surface of the ocean under bloom
conditions.
Some species of phytoplankton can have harmful effects on organisms at different
trophic levels. Blooms of some otherwise-harmless species result in massive fish kills by
depleting dissolved oxygen or by clogging the gills of fish. Within the Gulf of the
Farallones, the phytoplankton species that pose the greatest risk to marine life, and to
the humans who harvest various organisms within it, are those that produce marine
biotoxins. These natural toxins are concentrated in different species at different trophic
levels.
Bivalve shellfish (mussels, clams, scallops, oysters) and fish (anchovy, sardine) that
consume phytoplankton concentrate marine biotoxins, increasing the danger to the next
level of consumers (larger fish, seabirds, marine mammals, humans).Of the five major
groups of marine biotoxins known worldwide, two are known to occur along the
California coast. The PSP toxins, produced by the dinoflagellate Alexandrium catenella
have long been associated with bivalve shellfish in California.
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The other known toxin, domoic acid, was first identified along the Pacific coast of the
United States in 1991. Produced by the diatom Pseudonitzschia australis domoic acid
was responsible for the deaths of hundreds of brown pelicans and cormorants that fed
on toxic anchovy in Monterey Bay.
Alexandrium, followed by the rapid accumulation of PSP toxins in bivalve shellfish,
frequently originates in the southern Marin County coast near Drakes Bay. Large-scale
episodes of PSP toxicity appear to involve a northward progression of toxicity.
CONCLUSION
Phytoplankton are critical to the survival and growth of many species of marine life. At
certain times, the occurrence of a toxin-producing species of phytoplankton may affect
wildlife, causing illness or death. Human consumers of certain seafood items (especially
bivalve shellfish) are also at risk in the absence of adequate monitoring programs. Our
ability to understand and predict these natural events would greatly assist in the
protection of public health. Because the coastal area encompassed by the gulf has been
the focal point for PSP toxicity in California, and because of the continued increase in
commercial bivalve shellfish aquaculture within this area, CDHS has intensified its bio
toxin monitoring efforts in the area. The key to understanding the combination of
physical, chemical, and biological factors that result in blooms of the phytoplankton
species which produces PSP.
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Oceanography.
Academic
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Technology Enterprise. NTRS. Retrieved 16 June 2011.
"NASA Satellite Detects Red Glow to Map Global Ocean Plant Health" NASA, 28 May
2009.
"Satellite Sees Ocean Plants Increase, Coasts Greening". NASA. 2 March 2005. Retrieved 9
June 2014.
Henson, S. A.; et al. (2010). "Detection of anthropogenic climate change in satellite records
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Steinacher, M.; et al. (2010). "Projected 21st century decrease in marine productivity: a
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Richtel, M. (1 May 2007). "Recruiting Phytoplankton to Fight Global Warming". New York
Times.
See: Monastersky, R.: "Iron versus the greenhouse." Science News, 30 September 1995, p.
220.
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