Krill (Euphausiacea) demography and variability in abundance and distribution

Among euphausiids, there are many species that are represented by enormous numbers of individuals and are of considerable importance to various ecosystems, as well as to human exploitation. Considerable progress has been made regarding quantitative aspects of krill biology. This detailed knowledge about krill population parameters is necessary to answer questions about the importance of euphausiids to energy flow through certain ecosystems. This information also helps in assessing the importance of seasonal or long-term climate effects on variation in euphausiid populations because variability is not simply noise. Hypotheses have been developed as to how large seasonal or latitudinal environmental changes affect species survival strategies in poor conditions and maintenance of a stable population level. This paper discusses aspects of the spatial distribution with regard to seasonal and interannual changes, developments to define genetically distinct populations, and results of long-term variability in krill abundance and biomass for various species in different geographical locations.