Plankton are small organisms that drift or float in aquatic environments such as oceans, seas and bodies of fresh water. They play an important role in aquatic food webs as primary producers (phytoplankton) or primary consumers (zooplankton). Phytoplankton include algae like diatoms, dinoflagellates and cyanobacteria which produce oxygen and serve as the base of the food chain. Zooplankton include protozoa, rotifers, crustaceans and copepods which feed on phytoplankton and bacteria and are food for larger organisms. Plankton are crucial for marine ecosystems as they provide the base of the food web that supports many fish

1. Plankton, Types and Importance
by
ABIDA SAEED
DDF
Biology and Ecology
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2. Plankton, Introduction
• The term ‘plankton’ was first used by a German Scientist, Victor
Hensen (1887).
• The word plankton is derived from the Greek word ‘planktos’, meaning
for wanderer or drifters.
• These organisms are free floating with limited locomotory powers and
are transported horizontally with the mercy of the prevailing water
movements such as tides, waves and currents.
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3. • Plankton are such a kind of aquatic living organisms those are
small in size, generally microscopic, completely disassociated
from any substrata and subject to the movement of water
masses.
• The density of plankton is slightly greater than water.
• Small body size, large surface tension, possession of motive
organ and containing gas bubble (produced during biological
process), result in the suspension of plankton.
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4. Importance of Plankton
• Plankton are often used as indicator of environmental and aquatic
health because of their high sensitivity to changes such as
eutrophication and pollution with their short life span.
• Phytoplankton, also known as microalgae, are similar to terrestrial
plants in that they contain chlorophyll and require sunlight in order to
live and grow.
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5. • The microscopic plants and animals of the plankton family are the
foundation of freshwater and seawater food pyramids.
• Though they are microscopic in size, organisms called plankton play a
big role in marine ecosystems. They provide the base for the
entire marine food web.
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6. Role of Planktons in Fish Pond
• In aquatic ecosystem most important life form as for as food of fish
is concerned are planktons or natural food.
• In polyculture fish system Labeo rohita, Cirrhinus mrigala, Gibelion
catla and Hypopthalmichthys molitrix all feed on planktons.
• These species are known as planktivorous, planktophagic,
herbivorous or herbivore.
• In earthen fish pond seed nurseries/ hatcheries ponds primary
productivity/natural food of fish, plankton life is maintained by
fertilizing with organic and inorganic fertilizers.
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7. • In spite of fertilization practices natural food production for fish fry cannot
be optimized in earthen ponds because water loss through seepage and
fertility nutrients also leached down with percolation, resultantly optimum
fertility status of earthen ponds can never be achieved.
• Water retention is of universal importance regarding primary productivity
i.e., phytoplankton and zooplankton production. The more permeable the
soil, the greater the seepage, consequently removal of nutrients occurs
affecting primary productivity.
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8. Classification Of Plankton
I. Based On Nutrition
• 1. Phytoplankton
• Phytoplankton are the free floating organisms of the sea that are capable of photosynthesis
and synthesize organic matter as their food i.e. primary producers.
• Phytoplankton also contribute a significant portion of the oxygen found in the air we breathe.
• They are also known as microalgae and similar to terrestrial plants, they contain chlorophyll
and require sunlight in order to live and grow.
• Phytoplankters are microalgae, which includes diatoms, dinoflagellates, blue-green algae,
silico flagellates, etc.
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9. 2. Zooplankton
• Zooplankton are the various free floating animals, i.e. heterotrophic or
primary and secondary consumers.
• They are heterotrophic in nature as they depend on the already
formed organic matters for their source of food.
• Their food materials include phytoplankton, smaller or micro
zooplankton and detritus.
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10. • Zooplankton encompasses many different groups of animals
that range in size from microscopic crustaceans to jellyfish up to
a few feet across.
• Zooplankton forms an important and intermediate link in the
food web between primary producers and the higher trophic
levels. e.g., copepods, foraminiferans, siphanophores, eggs and
larvae of fishes, veligers of molluscs etc.
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11. II. Based on life history
• Zooplankton are further classified into two types
• 1.Holoplankton (Permanent Plankton)
• These are organisms that spend their entire lives in the plankton. These
are the permanent plankton organisms.
• This includes both phytoplankton and zooplankton, covering the whole
spectrum of plankton sizes and types. e.g. most phytoplankton, some
seaweeds, copepods, jelly fishes etc.
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12. 2. Meroplankton (Temporary plankton)
• These are organisms that spend only part of their life in the plankton.
• These include the larval forms of majority of benthic invertebrates and
nektonic forms.
• Often benthos have an early stage of the life history which is
planktonic, followed by a stage during which the plankton
metamorphoses into an organism which settles to the bottom.
• This includes species of seaweeds and kelps, and also crabs,
lobsters, clams, oysters, and worms among many others.
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13. III. Based on Size
1.Megaplankton - are organisms above 20 cm in size
2.Macroplankton - are organisms of cm in size range
3.Mesoplankton - fall between mm in size range
4.Microplankton - are organisms of µm in size range
5.Nanoplankton - are very small organisms ranging from 2-20 µm in
size.
6.Picoplankton - are minute organisms of µm in size
7.Femtoplankton - are still smaller organisms of µm in size.
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14. Phytoplankton: Important Groups of Algae
• Free floating organisms includes many microscopic algae
particularly
• Cyanophytes,
• Chlorophytes,
• Bacillariophytes
• Euglenophytes etc.
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15. Common Genera of Cyanophyta
• Microcystis sp.
• Anabaena sp.
• Nostoc sp.
• Oscillatoria sp.
• Merismopedia sp.
• Spirulina sp.
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16. Common Species of Cyanophyta
Anabaena sp.
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17. Common Genera of Chlorophyta
• Chlamydomonas sp.
• Pediastrum sp.
• Closterium sp.
• Cosmarium sp.
• Eudorina sp.
• Coelastrum sp.
• Chlorella sp.
• Scenedesmus sp.
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18. Common Species of Chlorophyta
Chlorella sp.
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19. Common Genera of Bacillariophyta or Diatoms
• Pinularia sp.
• Navicula sp.
• Nitzschia sp. 40 µm
• Melosira sp.
• Cyclotella sp.
• Chaetoceros sp.
• Tetraselmis chuii
• Skeletonemia sp
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20. Common Species of Diatoms or Bacillariophyta
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21. Common Genera of Euglenophyta
• Euglena sp.
• Phacus sp.
• Trachelomonas sp.
Dominant Species
• Euglena sanguinea
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22. Common Species of Euglenophyta
Euglena sp.
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23. Phytoplankton
• Phytoplankton are grouped under algae.
• There are several types of phytoplankton
• diatoms,
• dinoflagellates,
• blue-green algae, etc.
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24. 1.Diatoms (Class: Bacillariophyceae)
• They are unicellular and either chain forming or solitary.
• Diatoms with their characteristic yellow-brown pigment that masks their
green chlorophyll are also called golden algae.
• Diatoms may occur singly or they may occur in chains of various kinds.
• Diatoms reproduce mainly by simple fission.
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25. 2. Dinoflagellates (Class: Dinophyceaea)
• Dinoflagellates are very abundant next to diatoms.
• Like plants, they convert sunlight into food and however, like
animals, many varieties of dinoflagellates eat microscopic pieces of
matter found in the water.
• They reproduce by simple fission, as do the diatoms.
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26. 3. Cyanobacteria
• The blue-green algae, also called the cyanobacteria.
• Cyanobacteria are abundant in the tropics, where they occasionally
form dense mats of filaments and colour the water (red tide) by
Trichodesmium erythraeum.
• The abundant haptophytes are the coccolithophores, easily
distinguished by the tiny calcareous plates (coccoliths) on their outer
surface.
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27. 4. Planktonic Bacteria
• Pelagic bacteria or bacterioplankton, are also found in all oceans.
• They are usually found in association with organic particles in the
water column, collectively called Particulate Organic Carbon (POC),
or on various gelatinous zooplankton pieces known as marine snow.
• They decrease markedly with depth, and their role in the microbial
loop of the oceanic food web is now clearly recognized.
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28. Beneficial Effects of Phytoplankton
• They are very much important in the aquatic environments as these
are the basis of the life in any aquatic system.
• About 80 % of the oxygen on the earth is known to be produced by
these marine phytoplankton.
• They are also playing a major role in the cycling of biogeochemical in
the marine environment and hence these are of great significance on
the aspects of global warming.
• Phytoplankton cycles major nutrients in aquatic habitats.
• Phytoplankton are used as indicators of water quality.
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29. • Phytoplankton species are known to serve as indicators of some
commercially important fishery .
• For example, the abundance of diatom, Fragillaria oceanica in the plankton
samples is very high, then it is the indication of the presence of oil sardine fishes
(Sardinella longiceps) in that location.
• Similarly, the species of diatom Hemidiscus hardmanianus is observed to indicate
the fishery (lesser sardine) in the west coast of India.
• They are also known to serve as a food for the fish larvae in the hatcheries. e.g.
diatoms (Chaetoceros, Skeletonema), silicoflagellates (Isochrysis galbana) and
green algae (Chlorella).
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30. Harmful effects of Phytoplankton
• Some red tide causing dinoflagellates are toxic to the organisms of
higher trophic levels of the aquatic systems when they form bloom.
• They are responsible for the localized mass mortality of fishes in the
marine ecosystem.
• Besides the mass mortality of fishes, they are also responsible for the
transmission of some diseases to human beings particularly, PSP
(Paralytic Shellfish Poisoning), when the shell fish harvested from the
red tide affected coastal waters is consumed by human beings.
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31. Zooplankton
• Zooplankton is a complex group of aquatic animals.
• All are small in size, normally 40-3000 μm.
• Feed on tiny organisms, Heterotrophic (an organism that can not produce
its own food).
• Usually live in water column, and possess weak/active locomotivity, but
subject to water movement.
Four Groups
• Protozoa, Rotifera, Cladocera, Copepoda.
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32. Protozoa
• Protozoa are unicellular, usually 50-150 μm, few can reach 3 mm.
• Some species prey on bacteria while others eat algae
• They are able to perform various biological functions, such as:
metabolism, motion, reproduction, sensitive to light, feeding and so on.
• Each cell is an independent living organism.
• They are aerobic, need oxygen, but can tolerate very low oxygen level.
• As low as 10% of saturated concentration.
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33. Common Protozoan
Paramaecium sp.
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34. Rotifer
•Rotifera is a group of small multi-cellular animals.
•Body length: 40-2000 μm.
•Body is covered with chitinous membrane.
•Body is divided into Head (corona), Trunk and Foot or tail.
Common genera:
• Brachionus sp. Asplanchna sp. Schizocerea sp. Keratella sp.
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35. Common Species of Rotifers
Brachionus sp.
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36. Cladocera
• Small Crustacean, 0.2-3.0 mm in body length.
• Cladocera belong to Sub-class Branchiopoda,
• Class Crustacea
• Phylum Arthropoda
• Body has no clear body segmentation like many other groups in the
phylum. The trunk is covered with carapace. There is a pair of black
complex eyes on the head; Cladocera have a pair of well-developed
second antenna.
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37. Common genera:
• Daphnia sp.
• Scapholeberis sp.
• Bosmina sp.
• Moina sp.
• Ilyocryptus sp.
• Alona sp.
• Diaphanosoma sp.
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38. Common Cladocera
Daphnia sp.
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39. Copepoda
• Copepoda are small Crustacea with the body length of 0.3-3.0 mm.
• Copepoda is a Sub-class of Crustacea.
• The body is narrow and elongated.
• Distinct segmentation of the body.
• There is a Nauplius stage in the life cycle.
• That is very different from the adult in morphology.
• Five pairs of appendages attached to the thorax.
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40. Common genera of Copepoda
• Cyclops sp.
• Thermocyclops sp.
• Sinocalanus sp.
• Eodiaptonus sp.
• Canthocamptus sp.
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41. Common Copepoda
Nauplius stage
Adult Stage
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42. Major groups of freshwater zooplanktons
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43. Beneficial effects of Zooplankton
• Zooplankton are playing a pivotal role or as serving as an intermediate links in
the aquatic food chain and transfer the energy to the higher trophic levels.
• Zooplankton and other small marine creatures eat phytoplankton and then
become food for fish, crustaceans, and other larger species.
• Most of the zooplankton are serving as a very good food source to the larval
and adult fishes of the commercially important marine fishes.
• The abundance of the rich shoal of herrings and mackerels is indicated by the
abundance of copepod species Calanus.
• The presence of abundant krills (Euphausia superba) will indicate the presence
of baleen whales.
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44. Harmful effects of Zooplankton
• Some zooplankton are known to have some adverse effects on the fishery as
they are the voracious predators on the fish eggs and larvae, which may leads
to the poor fishery of that location e.g. Sagitta sp. (arrow worm).
• It is worth mentioning here that the abundance of jelly fishes in the sea is
considered as a menace or hindrance to the fishing operation as these are
known to clog the fish nets.
• Apart from this, the area rich in jelly fishes are also invariably observed to be
devoid of fishes.
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45. THANK YOU
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