Population structure and production of four sibling species ofPseudocalanusspp. in the Chukchi Sea

Copepods of the genus Pseudocalanus are important members of zooplankton communities in temperate and polar shelf regions, but few studies have focused on their species-specific biology due to the very subtle morphological differences between the species. We assess the distribution, population structure and production of four co-occurring species of Pseudocalanus across the Chukchi Sea during 2004, 2009 and 2012. Our approach used a combination of microscopic identification and species-specific polymerase chain reaction to discriminate between the species. Currently, the arctic P. acuspes dominates the genus (50–90%), with the relative distribution of species closely linked to water mass distribution and variations in physical properties, making Pseudocalanus important indicators of water mass origin. Although the temperate P. newmani had a significant presence throughout the Chukchi Sea, its stage distribution suggests that they recruit poorly in cold waters. Direct temperature-manipulation experiments further suggest that the reproductive activity of the two temperate species is inhibited at low temperatures, while the arctic P. acuspes exhibits reduced fitness and lower reproductive capacity when temperatures are increased to 10°C. Our results suggest that shifting oceanographic patterns and climate warming will have unequal impact on this genus, arising from species-specific differences in life histories and tolerance to environmental conditions.