Plankton

Plankton is any drifting organisms that are found in aquatic environments, which includes marine and fresh water. They are the base of the food chain for aquatic organisms such as fish and cetacean. Plankton food chain is responsible for the survival of many of the sea creatures. A fictional character of American cartoon series is named on this species and that is “SpongeBob SquarePants”.

Plankton can be divided into broad functional (or tropical level) groups:

• Phytoplankton: These are tiny algae that live near the water surface as there is sufficient light to support photosynthesis. They are usually unicellular. The more important groups among them are the diatoms, coccolithophores, cyanobacteria and dinoflagellates.

• Zooplankton: These are the small protists or metazoans (i.e., crustaceans and other animals). Small fishes consume the zooplanktons. 

• Bacterioplankton: These include bacteria and archaea, which play an important role in nutrient cycles in the water column.

The plankton is divided into the broad categories such as producer, consumer and recycler groups. Though most dinoflagellates are either photosynthetic producers or heterotrophic consumers, some can do both depending upon the circumstances. 

Among the plankton, holoplankton are those that spend their entire life cycle in the plankton, whereas meroplankton are those organisms that are planktonic for only part of their lives (generally the larval stage), and then move into the nekton or a benthic habitat. Some of the examples of meroplankton consist of larvae of sea urchins, starfish, clams, crustaceans, worms and most fish.

Planktons have a demerit that they are unable to swim against ocean currents like the fish and squid. They have a characteristic that they live in deeper water during the daylight, which provides protection from predators. This behavior is common in different phyla that are in the plankton. 

The abundance and distribution of plankton are strongly dependent on factors such as nutrient concentrations, the state of the water, and the abundance of other plankton. The primary sources, which are responsible for this variability, are the availability of light and nutrients. As springtime brings increased light and higher temperatures, this result in a spring bloom of phytoplankton, followed by zooplankton. During the summers, dead organisms sink to the bottom and then the bacteria and fungi both break down the tissues in the process of decay. The nutrients get restored, which concentrate on the bottom. Thus, the rate of photosynthesis declines. The warmer water stay on top and cooler water stays on the bottom. And if the water movements bring the regenerated nutrients up closer to the surface, then the phytoplankton bloom again. In the winter, temperatures fall and now the cooler surface water sinks down, and bottom water comes up. It causes the stratification to break down and another small bloom to occur.

Importance to Fish

Zoo plankton behaves as the initial prey for almost all the fish larvae. The density and distribution of these zoo plankton supports the life of the fish larvae, otherwise they will starve. If the zoo planktons get affected by the natural factors or man-made factors, then the result will be directly seen on larva’s life.