Zooplankton Groups
Zooplankton—animal plankton that drift with currents—range from protists (foraminifera, radiolarians) to crustaceans (copepods, krill, amphipods), jellyfish (cnidarians and ctenophores), larvae of bottom-dwelling organisms (meroplankton—including crab, fish, and sea urchin larvae), and gelatinous filter feeders (salps, larvaceans). Copepods are the dominant zooplankton globally, with over 13,000 species. A single copepod (1-2 mm long) can consume 120,000 diatom cells per day, converting plant carbon into animal tissue that fish can eat. Antarctic krill (Euphausia superba) form the largest animal biomass assemblages on Earth—swarms can cover hundreds of square kilometers and contain millions of tons of krill, directly feeding whales, penguins, seals, and seabirds.