Just like terrestrial organisms, marine organisms exist within complex food webs. The foundation for these food webs is the producers. Producers are organisms that are capable of producing organic compounds from inorganic compounds. In other words, the are the organisms that can make their own food. In marine ecosystems, the producers are phytoplankton, algae, grasses, mangroves, and chemoautotrophs.
Phytoplanktons are small unicellular plants that live in the ocean. Examples of phytoplankton are diatoms and dinoflagellates. These organisms are the basis of the marine food chain. Diatoms and dinoflagellates take in inorganic material and produce organic material (food) and oxygen. In fact, 75 – 85 % of the organic matter and 80% of the oxygen found in the ocean is produced by phytoplankton! Phytoplankton are most productive where there is the most sunlight. Typically the temperate zones have the greatest oceanic productivity.
Diatoms are single celled yellow-green algae. The name for these organisms comes from the Greek word diatom which means “cut in two.” This is because these organisms have a cell wall made up from silica with one half of the shell fitting over the other half like a lid over a box. Diatoms have different shapes, lines, and markings on their shells which distinguish them from one type and another. Their shape also allows them to float at the top of the water column to receive maximum sunlight. Some diatoms even use droplets of oil to help them stay afloat. Diatoms are also probably the single most important food source in the ocean. Diatoms are eaten by zooplankton, oysters, and clams.
Dinoflagellates are both animal and plant like. They are like animals because they have flagella which allow them to swim like simple animals. But they are also like plants because they perform photosynthesis. Dinoflagellates are the number two producer in the marine environment. However, dinoflagellates can also cause environmental concerns. Two species of dinoflagellates, Gonyaulax and Gymnodinium are responsible for a condition known as red tide. Red tide is a surge of these dinoflagellates that may cause fish and shellfish kills. This surge may sometimes cause the water to look red giving this condition its characteristic name. At night this surge may also cause the water to glow in the dark. This is because some dinoflagellates are bioluminescent, which means they can produce their own light.