PlanktonsPlanktons

Dr. Sameer G. ChebbiDr. Sameer G. Chebbi

Dept. of ZoologyDept. of Zoology

Karnatak Science College, DharwadKarnatak Science College, Dharwad

Planktons arePlanktons are marine and freshwater  marine and freshwater organisms that, because they are nonmotile or organisms that, because they are nonmotile or because they are too small or too weak to because they are too small or too weak to swim against the current, exist in a drifting, swim against the current, exist in a drifting, floating state. floating state.

The term The term planktonplankton is a collective name for all  is a collective name for all such organisms and includes certain such organisms and includes certain algaealgae, , bacteriabacteria, protozoans, crustaceans, molluscs, , protozoans, crustaceans, molluscs, and coelenterates, as well as representatives and coelenterates, as well as representatives from almost every other phylum of animals. from almost every other phylum of animals.

Plankton is distinguished from Plankton is distinguished from nektonnekton, which , which is composed of strong-swimming animals, and is composed of strong-swimming animals, and from from benthosbenthos, which includes sessile, creeping, , which includes sessile, creeping, and burrowing organisms on the seafloor. and burrowing organisms on the seafloor.

Large floating Large floating seaweedsseaweeds (for  (for example, example, SargassumSargassum, which constitutes the , which constitutes the Sargasso Sea) and various related multicellular Sargasso Sea) and various related multicellular algae are not considered plankton but algae are not considered plankton but pleustonpleuston. .

Organisms resting or swimming on the surface Organisms resting or swimming on the surface film of the water are called film of the water are called neustonneuston (e.g., the  (e.g., the alga alga OchromonasOchromonas).).

Plankton is the productive base of both marine Plankton is the productive base of both marine and freshwater and freshwater ecosystemsecosystems, providing food for , providing food for larger animals and indirectly for humans, larger animals and indirectly for humans, whose fisheries depend upon plankton. whose fisheries depend upon plankton.

As a human resource, plankton has only begun As a human resource, plankton has only begun to be developed and exploited. to be developed and exploited.

The chief food supply of the world, in view of The chief food supply of the world, in view of its high biological productivity and wide its high biological productivity and wide extent. extent.

It has been demonstrated on several occasions It has been demonstrated on several occasions that large-scale cultures of that large-scale cultures of algaealgae are  are technically feasible. technically feasible.

The unicellular green alga The unicellular green alga ChlorellaChlorella has been  has been used. used.

Through ample culture conditions, production Through ample culture conditions, production is directed toward is directed toward proteinprotein content greater than  content greater than 50 percent. 50 percent.

Although this protein has a suitable balance of Although this protein has a suitable balance of essential amino acids, its low degree of essential amino acids, its low degree of digestibility prevents practical use. digestibility prevents practical use.

Phytoplankton may become increasingly Phytoplankton may become increasingly important in space travel as a source for food important in space travel as a source for food and for gas exchange. and for gas exchange.

The carbon dioxide released during respiration The carbon dioxide released during respiration of spacecraft personnel would be transformed of spacecraft personnel would be transformed into organic substances by the algae, while the into organic substances by the algae, while the oxygen liberated during this process would oxygen liberated during this process would support human respiration.support human respiration.

Plankton are also often described in terms of size and Plankton are also often described in terms of size and usually the following divisions are used:usually the following divisions are used:

MegaplanktonMegaplankton > 20 cm > 20 cm metazoansmetazoans; e.g. ; e.g. jellyfishjellyfish; ; ctenophoresctenophores; ; salpssalps  and (  and (pyrosomespyrosomes pelagic  pelagic TunicataTunicata); ); CephalopodaCephalopoda;  ;  AmphipodaAmphipoda metazoansmetazoans; e.g. ; e.g. PteropodsPteropods;;

Macroplankton Macroplankton 2→20 cm 2→20 cm metazoansmetazoans; e.g. ; e.g. PteropodsPteropods; ; ChaetognathsChaetognaths; ; EuphausiaceaEuphausiacea ( (krillkrill); ); MedusaeMedusae; ; ctenophoresctenophores; ; salpssalps, doliolids and , doliolids and pyrosomespyrosomes(pelagic (pelagic TunicataTunicata); ); CephalopodaCephalopoda; ; JanthinidaeJanthinidae (one family gastropods);  (one family gastropods); AmphipodaAmphipoda metazoansmetazoans; e.g. ; e.g. copepodscopepods;  ; 

MesoplanktonMesoplankton 0.2→2 mm 0.2→2 mm MedusaeMedusae; ; CladoceraCladocera; ; OstracodaOstracoda; ; ChaetognathsChaetognaths; ; PteropodsPteropods;  ;  TunicataTunicata; ; HeteropodaHeteropoda, large , large eukaryoticeukaryotic  protistsprotists; most ; most phytoplanktonphytoplankton;  ; 

MicroplanktonMicroplankton 20→200  20→200 µmµm ProtozoaProtozoa  ForaminiferaForaminifera; ; tintinnidstintinnids; other ; other ciliatesciliates; ; RotiferaRotifera; juvenile ; juvenile metazoansmetazoans- - CrustaceaCrustacea ( (copepodcopepod nauplii) small  nauplii) small eukaryoticeukaryotic  protistsprotists; ;

NanoplanktonNanoplankton 2→20 µm Small 2→20 µm Small DiatomsDiatoms; ; Small Small FlagellatesFlagellates; ; PyrrophytaPyrrophyta; ; ChrysophytaChrysophyta; ; ChlorophytaChlorophyta; ; XanthophytaXanthophyta

PicoplanktonPicoplankton 0.2→2 µm 0.2→2 µm ChrysophytaChrysophyta

World distribution of planktonWorld distribution of plankton Plankton inhabit oceans, seas, lakes, ponds. Plankton inhabit oceans, seas, lakes, ponds. Local abundance varies horizontally, vertically Local abundance varies horizontally, vertically

and seasonally. and seasonally. The primary cause of this variability is the The primary cause of this variability is the

availability of light. availability of light. All plankton ecosystems are driven by the All plankton ecosystems are driven by the

input of solar energy (input of solar energy (chemosynthesischemosynthesis), ), confining primary production to surface confining primary production to surface waters, and to geographical regions and waters, and to geographical regions and seasons having abundant light.seasons having abundant light.

A secondary variable is nutrient availability. A secondary variable is nutrient availability. Although large areas of the Although large areas of the tropicaltropical and  and 

sub-tropicalsub-tropical oceans have abundant light, they  oceans have abundant light, they experience relatively low primary production experience relatively low primary production because they offer limited nutrients such as because they offer limited nutrients such as nitratenitrate, , phosphatephosphate and  and silicatesilicate. .

This results from large-scale This results from large-scale ocean circulationocean circulation and water column  and water column stratificationstratification..

In such regions, primary production usually In such regions, primary production usually occurs at greater depth, although at a reduced occurs at greater depth, although at a reduced level (because of reduced light).level (because of reduced light).

Despite significant Despite significant macronutrientmacronutrient concentrations,  concentrations, some ocean regions are unproductive. some ocean regions are unproductive.

The The micronutrientmicronutrient  ironiron is deficient in these regions,  is deficient in these regions, and adding it can lead to the formation of and adding it can lead to the formation of bloomsblooms of  of many kinds of phytoplankton. many kinds of phytoplankton. 

Iron primarily reaches the ocean through the Iron primarily reaches the ocean through the deposition of dust on the sea surface. deposition of dust on the sea surface.

Paradoxically, oceanic areas adjacent to Paradoxically, oceanic areas adjacent to unproductive, unproductive, aridarid land thus typically have abundant  land thus typically have abundant phytoplankton (e.g., the eastern phytoplankton (e.g., the eastern Atlantic OceanAtlantic Ocean, , where where trade windstrade winds bring dust from the  bring dust from the Sahara DesertSahara Desert in north  in north AfricaAfrica). ).

While plankton are most abundant in surface While plankton are most abundant in surface waters, they live throughout the water column. waters, they live throughout the water column.

At depths where no primary production At depths where no primary production occurs, occurs, zooplanktonzooplankton and  and bacterioplanktonbacterioplankton    instead consume organic material sinking from instead consume organic material sinking from more productive surface waters above. more productive surface waters above.

This flux of sinking material, so-called This flux of sinking material, so-called marine snowmarine snow, can be especially high following , can be especially high following the termination of the termination of spring bloomsspring blooms..

PhytoplanktonPhytoplankton Phytoplankton are free-floating microscopic Phytoplankton are free-floating microscopic

plants that are mostly unicellular and produce plants that are mostly unicellular and produce chemical energy from light. This process is chemical energy from light. This process is called called primary productionprimary production. .

The plant-like community of plankton is The plant-like community of plankton is called called phytoplanktonphytoplankton, and the animal-like , and the animal-like community is known as community is known as zooplanktonzooplankton. .

This convenient division is not without fault, This convenient division is not without fault, for strictly speaking, many planktonic for strictly speaking, many planktonic organisms are neither clearly organisms are neither clearly plantplant nor  nor animalanimal but rather are better described as  but rather are better described as protistsprotists. .

Phytoplankton have a critical role in primary Phytoplankton have a critical role in primary production, nutrient cycling, and production, nutrient cycling, and food websfood webs and make up a significant proportion of the  and make up a significant proportion of the primary production in aquatic systems.primary production in aquatic systems.

In many coastal systems, primary production In many coastal systems, primary production is almost entirely a function of the is almost entirely a function of the phytoplanktonphytoplankton. .

Even in salt marsh estuaries, where vascular Even in salt marsh estuaries, where vascular plant plant biomassbiomass can greatly exceed that of  can greatly exceed that of algaealgae, , phytoplankton can contribute substantially to phytoplankton can contribute substantially to overall primary production. overall primary production.

Phytoplankton are classified as microalgae and Phytoplankton are classified as microalgae and include species from the following divisions: include species from the following divisions:

Cyanobacteria (blue-green algae), Chlorophyta Cyanobacteria (blue-green algae), Chlorophyta (green algae), Prochlorophyta, Euglenophyta, (green algae), Prochlorophyta, Euglenophyta,

Pyrrhophyta (dinoflagellates ), Cryptophyta Pyrrhophyta (dinoflagellates ), Cryptophyta (cryptomonads), Chrysophyta, and (cryptomonads), Chrysophyta, and

Bacillariophyta (includes diatoms). Bacillariophyta (includes diatoms). Most phytoplankton are motile, however, Most phytoplankton are motile, however,

movement in the water column is mostly movement in the water column is mostly through transport by currents. through transport by currents.

Phytoplankton are usually grouped according to cell Phytoplankton are usually grouped according to cell size. Picoplankton are the smallest and are identified size. Picoplankton are the smallest and are identified as phytoplankton <2 micrometers (µm) in diameter. as phytoplankton <2 micrometers (µm) in diameter.

Nanoplankton are intermediate sized microalgae and Nanoplankton are intermediate sized microalgae and range in size from 2-20 µm. range in size from 2-20 µm.

Microplankton are the largest phytoplankton and Microplankton are the largest phytoplankton and include those algae >20 µm in diameter.include those algae >20 µm in diameter.

Freshwater phytoplankton, usually rich in green Freshwater phytoplankton, usually rich in green algae, also includes diatoms, blue-green algae, and algae, also includes diatoms, blue-green algae, and true flagellates.true flagellates.

In the oceans, phytoplankton In the oceans, phytoplankton biomassbiomass rises and falls  rises and falls according to multiyear cycles and appears to be according to multiyear cycles and appears to be sensitive to changes in sea surface temperatures. sensitive to changes in sea surface temperatures.

Microplankton are made up mostly of diatoms and Microplankton are made up mostly of diatoms and dinoflagellates. dinoflagellates.

Nanoplankton are dominated by phytoplankton with Nanoplankton are dominated by phytoplankton with flagellas (e.g. cryptophytes and chrysophytes, and flagellas (e.g. cryptophytes and chrysophytes, and prymnesiophytes). prymnesiophytes).

These plankters can account for 75% of the total These plankters can account for 75% of the total primary productivity of a system.primary productivity of a system.

Picoplankton are mostly prokaryotes such as Picoplankton are mostly prokaryotes such as cyanobacteria and prochlorophytes as well as cyanobacteria and prochlorophytes as well as several eukaryotic alga species. several eukaryotic alga species.

These tiny phytoplankters can account for as much as These tiny phytoplankters can account for as much as 50% of the primary production in oceanic waters. 50% of the primary production in oceanic waters.

ZooplanktonZooplankton The zooplankton is divided into two groups. The zooplankton is divided into two groups. Temporary plankton consists of planktonic Temporary plankton consists of planktonic

eggs and eggs and larvaelarvae of members of the  of members of the benthosbenthos and  and nekton; permanent plankton (nekton; permanent plankton (seesee  zooplankton videozooplankton video) includes all animals that ) includes all animals that live their complete live their complete lifelife cycles in a floating  cycles in a floating state. state.

The The temporary planktontemporary plankton, particularly abundant , particularly abundant in coastal areas, is characteristically seasonal in coastal areas, is characteristically seasonal in occurrence, though variations in spawning in occurrence, though variations in spawning time of different time of different speciesspecies ensure its presence in  ensure its presence in all seasons. all seasons.

Representatives from nearly every phylum of Representatives from nearly every phylum of the animal kingdom are found in the the animal kingdom are found in the permanent plankton. permanent plankton.

Among the Among the protozoansprotozoans, planktonic , planktonic foraminiferans and radiolarians are so foraminiferans and radiolarians are so abundant and widespread that their skeletons abundant and widespread that their skeletons constitute the bulk of bottom sediments over constitute the bulk of bottom sediments over wide ocean areas. wide ocean areas.

They are absent in fresh water. They are absent in fresh water. The ciliate protozoans are represented mainly The ciliate protozoans are represented mainly

by the tintinnids, which are between 20 and by the tintinnids, which are between 20 and 640 microns in size and sometimes occur in 640 microns in size and sometimes occur in vast numbers. vast numbers.

Among the planktonic coelenterates are the Among the planktonic coelenterates are the beautiful siphonophores (e.g., beautiful siphonophores (e.g., PhysaliaPhysalia, the , the Portuguese man-of-war) and the Portuguese man-of-war) and the jellyfishesjellyfishes. . Planktonic ctenophores, called comb jellies, or Planktonic ctenophores, called comb jellies, or sea walnuts, are also common. sea walnuts, are also common.

Freshwater rotifers may be present in plankton Freshwater rotifers may be present in plankton in vast numbers during the warmer seasons. in vast numbers during the warmer seasons.

A group of organisms that can be found at all A group of organisms that can be found at all latitudes, both in surface water and at great latitudes, both in surface water and at great depths, are the marine depths, are the marine arrowwormsarrowworms (e.g., (e.g.,SagittaSagitta), important planktonic predators. ), important planktonic predators.

Oysters, mussels, other marine Oysters, mussels, other marine bivalvesbivalves, and snails , and snails begin life as planktonic larvae. begin life as planktonic larvae.

The wing snails (Pteropoda) spend their entire life The wing snails (Pteropoda) spend their entire life cycles as plankton.cycles as plankton.

CrustaceansCrustaceans are the most important members of the  are the most important members of the zooplankton. They are the marine counterparts of zooplankton. They are the marine counterparts of insects on land; on land, as in the sea, the insects on land; on land, as in the sea, the arthropodsarthropods are the most diverse and numerous of all animal  are the most diverse and numerous of all animal phyla. phyla.

The The copepodcopepod  Calanus finmarchicusCalanus finmarchicus is important as  is important as food for the herring, and the euphausiid food for the herring, and the euphausiid Euphausia Euphausia superbasuperba, commonly known as , commonly known as krillkrill, is the main food , is the main food source for blue and finsource for blue and finwhaleswhales in the Antarctic Ocean.  in the Antarctic Ocean.

These whales, particularly blue and finback These whales, particularly blue and finback whales, migrate to waters where spawning of whales, migrate to waters where spawning of these crustaceans occurs; and the rapid growth these crustaceans occurs; and the rapid growth of these large mammals, feeding entirely on of these large mammals, feeding entirely on plankton, is impressive.plankton, is impressive.

There is a pronounced tendency for There is a pronounced tendency for zooplankton to perform diurnal vertical zooplankton to perform diurnal vertical migrations in both lakes and the sea. migrations in both lakes and the sea.

This migratory behaviour varies with stages in This migratory behaviour varies with stages in the life cycle, seasons of the year, latitude, the life cycle, seasons of the year, latitude, hydrographic structure, and meteorological hydrographic structure, and meteorological conditions. conditions.

Generally, the animals ascend toward the Generally, the animals ascend toward the surface at sunset from daytime depths. surface at sunset from daytime depths.

At midnight, if there is no optical stimulus At midnight, if there is no optical stimulus (e.g., moon, artificial light), some of the (e.g., moon, artificial light), some of the animals return to the daytime depths, then animals return to the daytime depths, then approach the surface once again just before approach the surface once again just before dawn. dawn.

As the sun rises, all descend to their daytime As the sun rises, all descend to their daytime level.level.

BacteriaBacteria and  and fungifungi Bacteria and fungi found in water belong by Bacteria and fungi found in water belong by

definition to plankton, but, because of special definition to plankton, but, because of special techniques required for sampling and identification, techniques required for sampling and identification, they usually are considered separately. they usually are considered separately.

These organisms are important in the transformation These organisms are important in the transformation of dead organic materials to inorganic plant nutrients. of dead organic materials to inorganic plant nutrients. Some of these marine and freshwater microorganisms Some of these marine and freshwater microorganisms (including blue-green algae) fix molecular (including blue-green algae) fix molecular nitrogennitrogen from water containing dissolved air, forming  from water containing dissolved air, forming ammonia or related nutrients important for ammonia or related nutrients important for phytoplankton growth. phytoplankton growth.

Although little is known about the extent of Although little is known about the extent of nitrogen fixation, bacteria and fungi always nitrogen fixation, bacteria and fungi always are found in water samples.are found in water samples.

A peculiar situation exists in the Black Sea, A peculiar situation exists in the Black Sea, where water below 130–180 metres (about where water below 130–180 metres (about 425–590 feet) contains hydrogen sulfide and 425–590 feet) contains hydrogen sulfide and no oxygen. no oxygen.

Under these conditions only bacteria are Under these conditions only bacteria are found. found.

Plankton and biological productivityPlankton and biological productivity The productivity of an area is dependent upon The productivity of an area is dependent upon

the availability of nutrients and water-stability the availability of nutrients and water-stability conditions. conditions.

Currents that flow near continents are Currents that flow near continents are important to plankton production in an area. important to plankton production in an area.

In the sea an adequate supply of nutrients, In the sea an adequate supply of nutrients, including carbon dioxide, enables including carbon dioxide, enables phytoplankton and benthic algae to transform phytoplankton and benthic algae to transform the the lightlight energy of the Sun into energy-rich  energy of the Sun into energy-rich chemical components through chemical components through photosynthesisphotosynthesis. .

The bottom-dwelling algae are responsible for The bottom-dwelling algae are responsible for about 2 percent of the primary production in about 2 percent of the primary production in the ocean; the remaining 98 percent is the ocean; the remaining 98 percent is attributable to phytoplankton. attributable to phytoplankton.

Most of the phytoplankton serves as food for Most of the phytoplankton serves as food for zooplankton, but some of it is carried below zooplankton, but some of it is carried below the light zone. the light zone.

After death, this phytoplankton undergoes After death, this phytoplankton undergoes chemical mineralization, bacterial breakdown, chemical mineralization, bacterial breakdown, or transformation into sediments. or transformation into sediments.

Phytoplankton production usually is greatest Phytoplankton production usually is greatest from 5 to 10 metres (16 to 33 feet) below the from 5 to 10 metres (16 to 33 feet) below the surface of the water. surface of the water.

High light intensity and the lack of nutrient in High light intensity and the lack of nutrient in the regions above a depth of 5 metres may be the regions above a depth of 5 metres may be the causes for suboptimal the causes for suboptimal photosynthesisphotosynthesis. .

Although bacteria are found at all depths, they Although bacteria are found at all depths, they are most abundant either immediately below are most abundant either immediately below great phytoplankton populations or just above great phytoplankton populations or just above the bottom.the bottom.

Biogeochemical significanceBiogeochemical significance Aside from representing the bottom few levels Aside from representing the bottom few levels

of a of a food chainfood chain that supports  that supports commerciallycommercially important  important fisheriesfisheries, plankton , plankton ecosystemsecosystems play  play a role in the a role in the biogeochemical cyclesbiogeochemical cycles of many  of many important important chemical elementschemical elements, including the , including the ocean's ocean's carbon cyclecarbon cycle..

Primarily by grazing on phytoplankton, Primarily by grazing on phytoplankton, zooplankton provide carbon to the planktic zooplankton provide carbon to the planktic foodwebfoodweb, either , either respiringrespiring it to provide  it to provide metabolicmetabolic energy, or upon death as  energy, or upon death as biomassbiomass or  or detritusdetritus. .

Organic material tends to be Organic material tends to be denserdenser than  than seawaterseawater, and as a result it sinks into open , and as a result it sinks into open ocean ecosystems away from the coastlines, ocean ecosystems away from the coastlines, transporting carbon along with it. transporting carbon along with it.

This process is known as the This process is known as the biological pumpbiological pump, , and it is one reason that oceans constitute the and it is one reason that oceans constitute the largest largest carbon sinkcarbon sink on  on EarthEarth..

It might be possible to increase the ocean's It might be possible to increase the ocean's uptake of uptake of carbon dioxidecarbon dioxide generated through  generated through human activitieshuman activities by increasing plankton  by increasing plankton production through production through seedingseeding, primarily with the , primarily with the micronutrientmicronutrient  ironiron. .

Acanthometron sp. Globigerina rubescens Brachionus plicatilis

Acrocalanus gracilis Acartia clausi

Megalopa Larva

Zooplankton

Bacteriastrum hyalinum Ceratium

Protoperidinium

Asterionellopsis glacialis