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Phytoplankton are the base of the marine food web and because they do not rely on other organisms for food, they make up the first trophic level. Organisms such as zooplankton feed on these phytoplankton which are in turn fed on by other organisms and so forth until the fourth trophic level is reached with apex predators.
When phytoplankton cells die, they sink towards the bottom and are decomposed by bacteria, a process that further reduces DO in the water column. If oxygen depletion progresses to hypoxia, fish kills can occur and invertebrates like worms and clams on the bottom may be killed as well. Still frame from an underwater video of the sea floor.
Around 70% of the oxygen in the atmosphere is produced in the oceans from phytoplankton performing photosynthesis, meaning that the majority of the oxygen available for us and other organisms that respire aerobically is produced by plankton. [71] Plankton also make up the base of the marine food web, providing food for all the trophic levels above.
Marine phytoplankton mostly inhabit sunlit surface waters as photoautotrophs, and require nutrients such as nitrogen and phosphorus, as well as sunlight to fix carbon and produce oxygen. However, some marine phytoplankton inhabit the deep sea, often near deep sea vents, as chemoautotrophs which use inorganic electron sources such as hydrogen ...
It has been estimated that half of the world's oxygen is produced by phytoplankton. [ 7 ] [ 8 ] Larger autotrophs, such as the seagrasses and macroalgae ( seaweeds ) are generally confined to the littoral zone and adjacent shallow waters, where they can attach to the underlying substrate but still be within the photic zone .
The word oxygen in the literature typically refers to molecular oxygen (O 2) since it is the common product or reactant of many biogeochemical redox reactions within the cycle. [37] Processes within the oxygen cycle are considered to be biological or geological and are evaluated as either a source (O 2 production) or sink (O 2 consumption). [36 ...
Since iron is necessary for phytoplankton growth, the auto-reduction of reactive oxygen species may be a way for algae to get usable iron from free or organically bound ferric iron. [73] For instance, Cakman et al. [ 74 ] showed that ROS may increase the amount of iron available through extracellular ferric reduction.
Ancestors of Prochlorococcus contributed to the production of early atmospheric oxygen. [26] Despite Prochlorococcus being one of the smallest types of marine phytoplankton in the world's oceans, its substantial number make it responsible for a major part of the oceans', world's photosynthesis, and oxygen production. [2]