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How do phytoplankton and zooplankton differ in marine food webs?
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Marine ecosystem
Zonation of the ocean. Note that in the littoral zone the water is at the high-tide mark.
In marine food webs, phytoplankton and zooplankton are distinguished primarily by their roles as producers and consumers, respectively.1
- Phytoplankton (Producers): These are plantlike organisms, such as diatoms and dinoflagellates, that perform photosynthesis. By harnessing sunlight, they convert inorganic substances into organic matter, serving as the foundational primary producers in the marine environment.21
- Zooplankton (Consumers): These are heterotrophic organisms, ranging from single-celled protists to larger animals like copepods and krill. As consumers, they feed on phytoplankton, other zooplankton, or organic matter.31
While this division is a useful ecological framework, it is simplified; some organisms are mixotrophic, and many planktonic species are better classified as protists rather than strictly plants or animals. Furthermore, zooplankton are categorized by their life cycles: holoplankton remain planktonic their entire lives, while meroplankton spend only their larval or juvenile stages drifting before transitioning to other habitats. Together, these groups form the base of the marine food web, supporting higher-level consumers such as fish and marine mammals.4135