Britannica
Sources used in this answer
- protozoan - Ecological and industrial importance of protozoans
- protist - Respiration and nutrition
- biosphere - The cycling of phosphorus and other essential nutrients
- marine ecosystem - The pelagic food chain
- protozoan - Mixotrophy in planktonic protozoans
- marine ecosystem - Links between the pelagic environments and the benthos
How do marine protozoans contribute to nutrient cycling?
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Protozoan
Amoeba (magnified).
Marine protozoans are fundamental to nutrient cycling in marine ecosystems, primarily by regulating populations of phytoplankton and bacteria. It is estimated that protozoans consume at least half of the phytoplankton production in marine waters.12
Their contribution to nutrient cycling occurs through several key processes:
- Nutrient Excretion: Planktonic protozoans excrete nitrogen and phosphorus at high rates as metabolic byproducts. This process is essential for recycling these nutrients back to phytoplankton, supporting continued primary production.1
- Bacterial Consumption: Many marine protozoans, including mixotrophs, feed voraciously on bacteria. Because bacteria are highly efficient at sequestering nutrients from the water, protozoans acquire these essential elements—including nitrogen, phosphorus, and vitamins—by consuming the bacteria.3
- Microbial Food Web: Heterotrophic protozoans are viewed as dominant controllers of both bacteria and primary production. By grazing on these microorganisms, they facilitate the flow of energy and nutrients within the complex microbial food web, which ultimately supports higher-level consumers.2