Marine Biology

Phytoplankton

Beneficial effects

•  Phytoplankton are very much important in the aquatic environments as these are the basis of the life in any aquatic system. Beingthe main primary producers in the marine ecosystem, they are often referred to as the grasses or pastures of the sea and also they form the base of the aquatic food chain, upon which all the marine life depends. 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 biogeochemicals in the marine environment and hence  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 as these are very sensitive to   even slight change in the environmental quality. 
• Phytoplankton species are known to serve as indicators of some commercially important fisheries .For example, very high abundance of diatom , Fragillaria oceanica in  plankton samples   indicates  the presence of oil sardine fishes (Sardinella longiceps) in that location. Similarly, the abundance of diatom species Hemidiscus hardmanianus   indicates the presence of lesser sardines which form the choodai fishery  in the west coast of India.

• They are also known to serve as a major live food item for  fish larvae in the hatcheries. E.g. diatoms(Chaetoceros, Skeletonema), silicoflagellates (Isochrysis galbana) and green algae (Chlorella).

Harmful effects

•      Some red-tide causing dinoflagellates ( Gonyaulax and Gymnodinium )  are toxic to the organisms of higher trophic levels of the aquatic systems when they form bloom . They are responsible for  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, when the shell fish harvested from the red-tide affected coastal waters  is consumed by human beings.