Copepoden

Copepods (Copepoda) are a diverse group of small crustaceans that form a major component of aquatic ecosystems. They occur in nearly every aquatic habitat, from the open ocean to freshwater bodies, and even moist terrestrial environments. Most copepods are less than 2 millimeters in length, though some species reach larger sizes. They are a principal part of the zooplankton and serve as a crucial link between phytoplankton and higher trophic levels, including fish larvae and invertebrates.

Morphology and development: Copepods typically have a compact body divided into a head and trunk, with paired thoracic appendages and a short abdomen. The first pair of antennae (antennules) are often large and used for swimming and feeding. A defining feature is their development through a nauplius stage, followed by several copepodid stages, with molts between stages. There are free-living planktonic forms as well as benthic and parasitic lineages.

Ecology and trophic roles: Free-living copepods graze on microalgae, bacteria, and microzooplankton, contributing to primary and secondary production. They are among the most abundant grazers in marine and freshwater systems and comprise a major prey item for many fish larvae and invertebrates. Parasitic copepods infect a wide range of hosts, including fish and other crustaceans, and can affect host health and aquaculture operations.

Taxonomy and diversity: Copepods are traditionally divided into orders such as Calanoida (predominantly planktonic), Cyclopoida, Harpacticoida, and Siphonostomatoida (many parasites). The group encompasses thousands of species with varied life histories and ecological niches.

Human relevance and applications: Copepods are used as model organisms in ecotoxicology and as live feed in aquaculture and ornamental fish culture. Their responses to environmental changes make them valuable indicators of water quality and ecosystem health.