Plankton is the foundation of the
ocean food web. The word plankton comes from the Greek word "planktos"
which means drifting. While some forms of plankton are capable of independent
movement and can swim up to several hundreds of metres vertically in a single
day, their horizontal position is primarily determined by currents in the body
of water they inhabit. Within the plankton itself, holoplankton are those
organisms that spend their entire life cycle as part of the plankton (e.g. most
algae, copepods, salps and jellyfish). By contrast, meroplankton are organisms
that are only planktonic for part of their lives (e.g. the larvae of sea
urchins, starfish, crustaceans, marine worms and most fish.
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| Plankton animals |
Functional groups
Plankton are primarily divided into
broad functional groups:
Phytoplankton – are autotrophic prokaryotic or
eukaryotic algae that live near the water surface where there is sufficient
light to support photosynthesis (e.g. diatoms, cyanobacteria and
dinoflagellates).
Zooplankton – are small protozoans or metazoans
(e.g. crustaceans and other animals) that feed on other plankton.
Bacterioplankton – bacteria and
archaea, which play an important role in remineralising organic material down
the water column (note that many phytoplankton are also bacterioplankton).
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