Scientists divide phytoplankton, or plant plankton, into three groups. Diatoms, dinoflagellates and microflagellates form the bottom of the aquatic food chain. Numbers of phytoplankton in an ocean might be so concentrated that they affect the color of the water and tint the water brown, green or red. Phytoplankton provide a necessary part of the aquatic food chain. Without phytoplankton, no other part of the food chain could exist. As producers of their own food through photosynthesis, they provide food to consumers larger than themselves who in turn provide food to the next creature up the food chain. They provide the first link in the plant, animal, human aquatic food chain.
The diatom phytoplankton classification contains more species than any other type. They live mainly in cooler water and often in large colonies. Diatoms can reproduce up to 100,000 times in a month. Diatoms are the largest of the phytoplankton and the fastest multipliers as well.
Diatoms have no means of locomotion through the water. When seen under a microscope, they have a clear, boxy shape. Their shell is made of silica, which encases chlorophyll and pigments that give them a gold tone. When the diatom dies, the silica shell sinks to the bottom of the ocean. There the layers of diatom shells form diatomaceous earth. This material, when harvested, is valuable as a gentle abrasive, filtration aide, additive in asphalt and concrete, as an insulator and as a pest control.
Dinoflagellates create another phytoplankton group. This type of phytoplankton lives mainly in tropical waters. Dinoflagellates can move through the water using two flagellae or tiny whip-like protrusions that help them twist and spin through the water in search of sunlight needed for photosynthesis. Some dinoflagellates however, absorb nutrients through water rather than using photosynthesis.
About 2,000 species of dinoflagellates exist. Some have extensive, ornate shapes. Additionally, about 60 species are toxic. At times, these dinoflagellates reproduce at a heightened rate in what scientists call a bloom. These huge masses of dinoflagellates, particularly those that are toxic, cause ecosystem problems for plant, animal and human life. One such type of bloom is called red tide and is common during summer months along the U.S. Gulf Coast.
Microflagellates, similar to dinoflagellates except smaller, also have flagellae and some ability to move about in the water. Microflagellates however, divide more slowly than the other groups. They also inhabit tropical waters and can reproduce successfully with little nutrient support. Scientists think that they form the basis of the marine food chain as the smallest photosynthesis producers.