Copepods are one of our most popular live foods and before people purchase them for the first time, it is common to have questions about them. Although they have heard they are undoubtedly great for the health of their tank, many people are unsure about what copepods really do for their tank and what to expect when adding them into the mix. So we are here to answer the main questions people have about Copepods and explain all you need to know before purchasing these creatures.
What is a Copepod?
So let’s start with the basics. Copepods are small aquatic crustaceans and are one of the most numerous metazoan groups in aquatic communities. Copepods inhabit a huge range of salinities, from fresh water to hypersaline conditions, and they can be found virtually everywhere there is water; from subterranean caves to pools collected in bromeliad leaves or in damp leaf litter on the ground, from streams, rivers, and lakes to the open ocean and the sediment layers beneath. Their habitats range from the highest mountain lakes to the deepest ocean trenches and from the cold polar ice-water interface to the hot active hydrothermal vents. Copepods may be free-living, symbiotic, or internal or external parasites on almost every major metazoan phylum. Adults typically have a body length in the 1-2 mm range, but adults of free-living species may be as short as 0.2 mm
There are currently 10 Orders of Copepod:
The second pair of cephalic appendages in free-living copepods is usually the main time-averaged source of propulsion, beating like oars to pull the animal through the water. However, different groups have different modes of feeding and locomotion, ranging from almost immotile for several minutes (e.g. some harpacticoid copepods) to intermittent motion (e.g., some cyclopoid copepods) and continuous displacements with some escape reactions (e.g. most calanoid copepods
What do Copepods eat?
Most free-living copepods feed directly on phytoplankton, catching cells individually. A single copepod can consume up to 373,000 phytoplanktons per day. They generally have to clear the equivalent to about a million times their own body volume of water every day to cover their nutritional needs. 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 mouth parts 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 on plankton blooms. These droplets may take up over half of the volume of their bodies in polar species.
What is the Lifecycle of a Copepod?
Most copepods are holoplanktonic, meaning they stay planktonic for all of their lifecycles, although harpacticoids, although free-living, tend to be benthic rather than planktonic. During mating, the male copepod grips the female with his first pair of antennae, which is sometimes modified for this purpose. The male then produces an adhesive package of sperm and transfers it to the female’s genital opening with his thoracic limbs. Eggs are sometimes laid directly into the water, but many species enclose them within a sac attached to the female’s body until they hatch. In some pond-dwelling species, the eggs have a tough shell and can lie dormant for extended periods if the pond dries up.
Ecology of a Copepod
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 such as the dragonet, banded killifish, Alaska pollock, and other crustaceans such as krill in the ocean and in fresh water. Some scientists say they form the largest animal biomass on earth.
Because of their smaller size and relatively faster growth rates, 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 more 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 tons of carbon a year, the equivalent to perhaps a third of human carbon emissions, thus reducing their impact.