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Copepod
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Copepods are a group of small crustaceans found in the sea and nearly every freshwater habitat. Many species are planktonic (drifting in sea waters), but more are benthic (living on the ocean floor), and some continental species may live in limno-terrestrial habitats and other wet terrestrial places, such as swamps, under leaf fall in wet forests, bogs, springs, ephemeral ponds and puddles, damp moss, or water-filled recesses (phytotelmata) of plants such as bromeliads and pitcher plants.
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Encyclopedia
Copepods are a group of small crustaceans found in the sea and nearly every freshwater habitat. Many species are planktonic (drifting in sea waters), but more are benthic (living on the ocean floor), and some continental species may live in limno-terrestrial habitats and other wet terrestrial places, such as swamps, under leaf fall in wet forests, bogs, springs, ephemeral ponds and puddles, damp moss, or water-filled recesses (phytotelmata) of plants such as bromeliads and pitcher plants. Many live underground in marine and freshwater caves, sinkholes, or stream beds. Copepods are sometimes used as bioindicators (see particle (ecology)).
Ecology
Planktonic copepods are important to global ecology and the carbon cycle; They are usually the dominant members of the zooplankton, and are major food organisms for small fish, whales, seabirds and other crustaceans such as krill in the ocean and in fresh water. Some scientists say they form the largest animal biomass on earth. They compete for this title with Antarctic krill (Euphausia superba). Because of their smaller size and relatively faster growth rates, however, and because they are more evenly distributed throughout more of the world's oceans, copepods almost certainly contribute far more to the secondary productivity of the world's oceans, and to the global ocean carbon sink than krill, and perhaps than all other groups of organisms together. The surface layers of the oceans are currently believed to be the world's largest carbon sink, absorbing about 2 billion tonnes of carbon a year, the equivalent to perhaps a third of human carbon emissions, thus reducing their impact. Many planktonic copepods feed near the surface at night, then sink into deeper water during the day to avoid visual predators. Their moulted exoskeletons, faecal pellets and respiration at depth all bring carbon to the deep sea.
About half of the estimated 13,000 described species of copepods are parasitic and have strongly modified bodies. They attach themselves to fish, sharks, marine mammals, and many kinds of invertebrates such as molluscs, tunicates, or corals. They live as endo- or ectoparasites on fish or invertebrates in fresh water as well as in marine environments.
Characteristics
Copepods are typically to long, with a teardrop shaped body and large antennae. Although like other crustaceans they have an armoured exoskeleton, they are so small that in most species this armour, and the entire body, is almost totally transparent. Some polar copepods reach . Copepods have a compound, median single eye, usually bright red and in the centre of the transparent head; subterranean species may be eyeless. Many of the smaller copepods feed directly on phytoplankton, catching cells singly. Some of the larger species are predators of their smaller relatives. Many benthic copepods eat organic detritus or the bacteria that grow in it, and their mouthparts are adapted for scraping and biting. Herbivorous copepods, particularly those in rich cold seas, store up energy from their food as oil droplets while they feed in the spring and summer plankton blooms. These droplets may take up over half of the volume of the body in polar species.
Many species have neurons surrounded by myelin, which is very rare among invertebrates (other examples are some annelids and malacostracan crustaceans like palaemonid shrimp and penaeids). Even rarer, the myelin is highly organized, resembling the well-organized wrapping found in vertebrates (Gnathostomata).
Some copepods are very evasive and can jump with extreme speed over a few millimeters (see animated image).
This scene was scanned with the ecoSCOPE, an underwater high speed microscope. Very little is known about the details of these kinds of predator/prey interactions, in spite of their importance for global processes, because copepods are difficult to keep in the laboratory and lose most of their escape capacity, and herring are very fast, alert and evasive organisms and flee from normal camera systems or scuba divers.
Classification
Copepods form a subclass belonging to the subphylum Crustacea (crustaceans). Some authors consider the copepods to be a full class. The group contains ten orders with some 14,000 described species. A scientist that studies copepods is a copepodologist.
Copepods in Marine Aquariums
Live copepods are used in the saltwater aquarium hobby as a food source and are generally considered beneficial in most reef tanks. They are scavengers that feed on algae, including coralline algae.
Live copepods are popular among hobbyists who are attempting to keep particularly difficult species such as the mandarin dragonet, or to breed other marine species in captivity. In a saltwater aquarium, copepods are typically stocked in the refugium.
Water supply
Copepods are sometimes found in the public mains water supply, especially systems where the water is not filtered, such as New York City and Boston, Massachusetts. This is not usually a problem in treated water supplies. In some tropical countries, such as Peru and Bangladesh, a correlation has been found between copepods and cholera in untreated water, because the cholera bacteria attach to the surfaces of planktonic animals. The risk of cholera from infected water can be reduced by filtering out the copepods (and other matter), for example with a cloth filter.
Copepods have been used successfully in Vietnam to control disease-bearing mosquitoes such as Aedes aegypti that transmit dengue fever and other human parasitic diseases.
The copepods can be added to water-storage containers where the mosquitoes breed. Copepods, primarily of the genera Mesocyclops and Macrocyclops, can survive for periods of months in the containers, if the containers are not completely drained by their users. They will attack, kill, and eat the younger 1st and 2nd instar larvae of the mosquitoes. This biological control method is complemented by community trash removal and recycling to eliminate other possible mosquito-breeding sites. Because the water in these containers is drawn from uncontaminated sources such as rainfall, there is little risk of contamination by cholera bacteria, and in fact no cases of cholera have been linked to copepods introduced into water-storage containers. Trials using copepods to control container-breeding mosquitoes are underway in several other countries, including Thailand and the southern United States.
The matter of copepods in the water supply, however, has raised a peculiar problem for Jews who observe Kashrut in that copepods, being crustaceans, are not kosher, and are not small enough to be ignored as non-food microscopic organisms (since some specimens can be seen with the naked eye). The discovery of copepods in the New York water supply in the summer of 2004 in particular caused significant debate in rabbinical circles and caused many observant Jews to buy filters for their water.
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See also
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