Copepods
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Calanoida |
Copepods are small, aquatic animals living in the sea and nearly every freshwater habitat, a form of plankton, specifically zooplankton. Some copepods are parasitic.
Copepods form a subclass belonging to the subphylum crustaceans (some authors consider the copepods as a full class). The group contains 10 orders with some 14 000 described species.
Copepods are very important food organisms for small fish, whales and other crustaceans in the ocean. They are typically 1-2 mm long. They feed directly on phytoplankton and catch with their feeding legs single cells from the water. Some scientists say they form the largest animal biomass on earth. They compete for this title with the Antarctic krill Euphausia superba.
Copepods are commonly found in the public mains water supply. This is not usually a problem in treated water supplies, although a correlation has been found between copepods and cholera in untreated water.
As copepods are crustaceans, they are not regarded as kosher, which can cause problems for observant Jews in areas where copepods are present in the public water supply. This can be remedied by filtering the water.
Copepods are very evasive and can jump with extreme speed over a few millimeters:
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Slow motion macrophotography video (50 %) of juvenile Atlantic herring (38 mm) feeding on copepods - the fish approach from below and catch each copepod individually. In the middle of the image a copepod escapes successfully to the left.
This scene was scanned with the ecoSCOPE, an underwater high speed microscope. As clupeids (herrings) and copepods are amongst the biggest biomasses of the planet this is the first record of what is probably the largest carbon flow of any animal food chain transition in the oceans. It is a predator / prey relationship running at extreme speeds, with chances for both sides. Very little is known about the details, in spite of its importance for global processes, because copepods are very difficult to keep in the laboratory and lose most of their escape capacity, and herring are very fast, alert and evasive organisms and flee normal camera systems or SCUBA divers. Oceanographers point out the importance to learn more about the influences of physical parameters, like light, pollution or temperature, or the effects of hunting in a swarm, If the copepod wins, much carbon will sink with its fecal pellets into the depth of the oceans (biological pump), sequestering CO2, if the herring wins, much carbon will flow up the foodchains of the upper biosphere and return via respiration. Such work and new in situ instrumentation developments are projected in the international GLOBEC projects.
Copepods as bioindicators: particle (ecology)