Seasonal size distribution of developmental stages of sub-antarctic copepod

Drepanopus pectinatus, the most numerous species of Copepod in the Kerguelen Archipelago completes 4 generations a year. The succession of generations follows the hydrological seasons. Each generation may be characterized by the cephalothorax length of the developmental stages C1 to C6. The mean lengths of stages C2 to C6 are shown to be significantly different (P > 0.05) between seasons (i.e. between generations). The size-classes have a unimodal distribution from stages C1 to C4. For copepodite C5 and adults, bimodal histograms reflect the differentiation of males and females.A reverse trend of the development pattern of lengths is demonstrated in this subantarctic species: a decrease with decreasing temperatures (6° to 2°) from April to September, and an increase with the rising temperatures (2° to 7°) from October to February.Two populations of females are distinguishable in spring and summer, by their small (0.950–1.299 mm length of cephalothorax, 55%) or large (1.300–1.800 mm, 45%) size, respectively.The differences in mean length cannot be explained by their relation to the mean temperature alone. Pigment content is suspected to play a role.