Bathymetric adaptations of life history patterns of congeneric species (Euchaeta: Calanoida) in a 2000m water column

Earlier studies of micronektonic crustaceans and fish showed that breeding is aseasonal, fecundity is reduced and generation time is lengthened in the bathypelagic zone; no response to seasonal epipelagic production was detectable. This article examines 12 bathymetrically partitioned copepod species in the genus Euchaeta. Prosome length and brood volume are not related to modal depth of occurrence of Euchaeta species. Mean prosome length of E. norvegica, whose bathymetric range extends from 400 to 1800 m, increases with depth. Between-species comparisons of spermatophore length, egg diameter, and generation time are positively correlated with depth and considered to result from the decreasing temperature regimes. Variation in prosome and spermatophore lengths, spermatophore production, and amplitude of seasonal change in prosome length are all negatively correlated with depth. These negative correlations are considered to reflect increasing environmental stability and decreasing influence of epipelagic seasonality.