The decomposers in an underwater ecosystem are animal-like organisms called protists, fungi and bacteria. Referred to as saprotrophs, these organisms decompose dead matter from higher-level plants and animals, facilitating the re-entry of nutrients into the ecosystem in the form of raw nutrients and carbon dioxide.
In the underwater ecosystem, plants and animals leave behind valuable nutrients when they die. These nutrients are an important energy source for the entire ecosystem. For the ecosystem to stay healthy, the energy contained in the dead organic matter, called detritus, must be reabsorbed. The decomposition process begins by scavengers known as detrivores, who feed on easily consumable organic matter. Protists, fungi and bacteria then complete the decomposition process by breaking down harder-to-digest materials, such as bones.
Decomposers eventually break down everything they consume into base nutrients and carbon dioxide. The raw nutrients, such as magnesium, nitrogen and phosphorous, are released back into the ecosystem in a form that producers such as oceanic chemosynthetic bacteria can survive on. These bacteria, in turn, are important sources of nutrition for organisms such as clams and mussels. Nutrients released by saprophrotic decomposers also assist in plankton blooming, which is important for the survival of large ocean mammals such as whales.