Phytoplankton – The base of marine food webs
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Phytoplankton…. If you are a marine biologist like me you may familiar with this term and you know how important they are to the existence of the marine food webs since they are grass root energy suppliers. Unfortunately they are not popular among general public as dolphins and whales.
So through this article I am going to provide general overview about these tiny but valuable creatures.
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Who are they?
Phytoplankton are microscopic, photosynthetic organisms and they cannot propel through the water by themselves. They are single celled organisms and their cell or colony sizes range from, 1µm to several cm. So we cannot observe them though our naked eye.
Why do we need to talk about them?
Phytoplankton are at the bottom of food chains. So they are the driving force of marine food webs. So changes in their abundance, composition and density can have a great influence on the health of marine ecosystem and food supply. In the other hand they sequester CO2 through photosynthesis and help to regulate the climate change. At the same time they are considered as the indicators of the water quality.
Biology of phytoplankton
Phytoplankton world is diverse. It consists of both eukaryotic groups (diatoms, dinoflagellates, green algae) and one prokaryotic group (cyanobacteria). Although flagella present in some species they mainly move through the water by using water currents. All most all the phytoplankton are not autotrophic. There are some mixotrophic and heterotrophic species as well. Light, nutrient and animal grazing determine the phytoplankton density in water. Although they live in photic zone and they need sunlight for the photosynthesis; too much sunlight damage them. Growth and the phytoplankton species composition is determined by the N:P:Si ratio in the ocean. However in some parts of the Pacific and Southern ocean phytoplankton abundance has hindered due to the lack of micro nutrient Fe. These areas are called as High Nutrient Low Chlorophyll (HNLC) areas.
In mid-latitudes, phytoplankton increase in spring, decline in summer and may increase to a lesser extent in fall. Zooplankton and filtering benthic animals depend on phytoplankton while bacteria degrade them by fertilizing the ocean. So their density and blooming period is determined by the phytoplankton abundance.