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What Is Plankton?

  • Plankton is the diverse collection of organisms found in water (or air) that cannot propel themselves against a current (or wind). The individual organisms constituting plankton are called plankters.
  • Includes both microscopic plants like algae (phytoplankton) and animals like crustaceans and protozoans (zooplankton) found in all aquatic ecosystems, except certain swift moving waters.
  • The planktons' locomotory power is limited so that their distribution is controlled largely by currents in the aquatic ecosystems.
    (i) The growth rate, productivity and species diversity of plankton in tropical waters especially in mangrove waters are high.

Phytoplankton

  • Derived from the Greek words phyto (plant) and plankton (made to wander or drift), phytoplankton are microscopic plant organisms that live in aquatic environments, both salty and fresh.
  • Some phytoplankton are bacteria, some are protists, and most are single-celled plants. Among the common kinds are cyanobacteria, silica-encased diatoms, dinoflagellates, green algae, and chalk-coated coccolithophores.
  • Phytoplankton produce more than 60% of oxygen produced from all plants.
  • Like land plants, all phytoplankton have chlorophyll to capture sunlight, and they use photosynthesis to turn it into chemical energy. They consume carbon dioxide, and release oxygen. All phytoplankton photosynthesize, but some get additional energy by consuming other organisms.
  • These micro-algae are present throughout the lighted regions of all the seas and oceans including the Polar Regions.
  • Their total biomass is many times greater than that of the total plants on land and they serve as the “pasture grounds” in the aquatic environment.

Factors Affecting Phytoplanktons Biodiversity

Light

  • Phytoplanktons are limited to the ocean's uppermost layers where light intensity is sufficient for photosynthesis to take place.
  • The photosynthetic rate varies with light intensity. 

Nutrients

  • The major inorganic nutrients required by phytoplankton for growth and reproduction are nitrogen and phosphorus.
  • Diatoms and silicoflagellates also require silicate (SiO2) in significant amounts.
  • Some phytoplankton can fix nitrogen and can grow in areas where nitrate concentrations are low.
  • They also require trace amounts of iron which limits phytoplankton growth in large areas of the ocean because iron concentrations are very low. 

Temperature

  • Temperature acts along with other factors in influencing the variation of photosynthetic production.
  • Generally, the photosynthesis rate increases with an increase in temperature, but diminishes sharply after a point is reached.
  • Temperature, together with illumination, influences the seasonal variation of phytoplankton production in the temperate latitudes.

Salinity

  • Besides light and temperature, salinity also is known to influence primary production.
  • Grazing by Zooplankton
  • The grazing rate of zooplankton is one of t he major factors influencing the size of the standing crop of phytoplankton, thereby reducing production rate.

Distribution

  • Marine phytoplankton are not uniformly distributed throughout the oceans of the world. The highest concentrations are found at high latitudes, except upwelling areas on the continental shelves, while the tropics and subtropics have 10 to 100 times lower concentrations.
  • In addition to nutrients, temperature, salinity and light availability; the high levels of exposure to solar UV-B radiation that normally occur within the tropics and subtropics may play a role in phytoplankton distributions.
  • Phytoplankton productivity is limited to the euphotic zone, the upper layer of the water column in which there is sufficient sunlight to support net productivity.
  • The position of the organisms in the euphotic zone is influenced by the action of wind and waves. 

Importance of phytoplankton

The food web

  • Phytoplanktons are the foundation of the aquatic food web, the primary producers feed everything from microscopic animal-like zooplankton to whales. Small fish and invertebrates graze on the phytoplanktons, and then those smaller animals are eaten by bigger ones.

Phytoplankton - the Carbon Cycle and climate change

  • 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 carbon is returned to near-surface waters when phytoplankton is eaten or decomposed, but some fall 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 phytoplankton growth may affect atmospheric carbon dioxide concentrations, which would feed back to global surface temperatures.

What Is Zooplankton?

  • Zooplankton plays a vital role in the food chain of the food chain, nutrient recycling, and the transfer of organic matter from primary producers to secondary consumers like fishes.
  • They are more abundant within mangrove water-ways than in adjacent coastal waters, and a large proportion of the juvenile fish of mangrove habitat are zooplanktivorous.
  • The zooplankton determine the quantum of fish stock. Hence, based on their quality and species diversity, zooplankton communities are used for assessing the productivity vis-à- vis fishery resource, fertility, and health status of the ecosystem.
  • Tiny flagellates, giant jelly fish (>50 μm).

Sea-Grass

  • Sea grasses are (angiosperms) marine flowering plants that resemble grass in appearance.
  • They produce flowers; have strap-like or oval leaves and a root system.
  • They grow in shallow coastal waters with sandy or muddy bottoms & require comparatively calm areas.
  • They are the only group of higher plants adapted to life in the salt water.
  • Major Sea grass meadows in India occur along the south east coast of Tamil Nadu and in a few Lakshadweep Islands' lagoons. There are few grass beds around Andaman and Nicobar islands also.
  • The rich growth of seagrasses a long the Tamil Nadu coast and Lakshadweep islands is mainly due to high salinity, clarity of the water and sandy substratum.

 Functions

  • Sea grass beds physically help
    (i) to reduce wave and current energy,
    (ii) to filter suspended sediments from the water and
    (iii) stabilise bottom sediments to control erosion.
  • Provides habitat for marine invertebrates and fishes.
  • Seagrass beds are widespread in lagoon & in such areas, the population of fish and migratory birds are also higher due to the availability of food and shelter.
  • Sea grasses on reef flats and near estuaries are also nutrient sinks, buffering or filtering nutrient and chemical inputs to the marine environment.

IUCN has accorded high priority for the conservation of sea grass.

Out of 58 species found globally, Fourteen species of seagrasses have been recorded from Indian coast.

They are commonly distributed from inter-tidal to sub-tidal region down to 8 m depth.

Dugong, a mammal dependent on sea grass for food, is also on the verge of extinction.

 Threats to sea grass beds

  • Eutrophication, siltation, trawling, coastal engineering constructions and over exploitation for commercial purposes are the major threats for sea grass beds.

Management

  • The major seagrass beds should be mapped and areas has to be identified for preservation.
  • Dredging should be carried out far away from seagrass beds as siltation /turbidity destroys seagrass beds.

Seaweeds

  • Seaweeds are (thalloid plants) macroscopic algae, which mean they have no differentiation of true tissues such as roots, stems and leaves. They have leaf-like appendages. 
  • Seaweeds, the larger and visible marine plants are found attached to rocks, corals, and other submerged strata in the sea's intertidal and shallow sub tidal zones.
  • Seaweeds grow in shallow coastal waters wherever sizable substata is available.
  • Based on the colour of their pigmentation, sea weeds are broadly classified into different classes such as
    (i) blue- green,
    (ii) green,
    (iii) brown,
    (iv) red etc.

Functions of seaweeds

  • Food for marine organism, 
  • habitat for fish breeding grounds,
  • Source of sediment.

 Uses of seaweeds

  • Seaweeds are important as food for humans, feed for animals, and fertilizer for plants.
  • Seaweeds are used as a drug for goiter treatment, intestinal and stomach disorders.
  • Products like agar-agar and alginates, iodine which are of commercial value, are extracted from seaweeds.
  • By the biodegradation of seaweeds methane like economically important gases can be produced in large quantities.
  • Extracts of some seaweed species show antibacterial activity.
  • Seaweeds are also used as the potential indicators of pollution in coastal ecosystem, particularly heavy metal pollution due to their ability to bind and accumulate metals strongly.

Harmful effects of seaweeds

  • Rotting seaweed is a potent source of hydrogen sulfide, a highly toxic gas, and has been implicated in some incidents of apparent hydrogen-sulphide poisoning. It can cause vomiting and diarrhoea.

 Threats to seaweeds

  • Threats are similar to that of sea grass.
The document Marine Organisms | Environment for UPSC CSE is a part of the UPSC Course Environment for UPSC CSE.
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FAQs on Marine Organisms - Environment for UPSC CSE

1. What is plankton?
Ans. Plankton refers to small organisms that drift in water bodies, including oceans, lakes, and rivers. They are unable to swim against the current and rely on water movements to move. Plankton can be broadly classified into two main groups: phytoplankton, which are microscopic plants, and zooplankton, which are tiny animals.
2. What are phytoplankton?
Ans. Phytoplankton are microscopic plants that form the base of the marine food web. They are primarily composed of algae and other photosynthetic organisms. Phytoplankton derive energy from the sun through photosynthesis and play a crucial role in producing oxygen and absorbing carbon dioxide, contributing to the Earth's climate regulation.
3. How do phytoplankton contribute to the marine ecosystem?
Ans. Phytoplankton are essential to the marine ecosystem as they are the primary producers of organic matter. They form the basis of the food chain, providing nourishment for zooplankton, which are then consumed by larger animals. Additionally, phytoplankton play a crucial role in carbon cycling, absorbing carbon dioxide from the atmosphere and helping to regulate the Earth's climate.
4. Can phytoplankton be harmful?
Ans. While phytoplankton are vital to marine ecosystems, certain species can produce harmful algal blooms (HABs). These blooms can release toxins that are harmful to marine life, including fish, mammals, and even humans. HABs can cause fish kills, contaminate shellfish with toxins, and lead to oxygen depletion in the water, resulting in dead zones.
5. How are phytoplankton affected by climate change?
Ans. Climate change can have significant impacts on phytoplankton populations. Rising sea surface temperatures, increased ocean acidification, and changes in nutrient availability can affect the growth and distribution of phytoplankton. Some studies suggest that climate change may favor certain harmful algal species, leading to an increase in harmful algal blooms and potential ecological disruptions.
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