Mortality rates of epipelagic copepods in the post-spring bloom period in Disko Bay, western Greenland

Mortality rates of the copepods Calanus hyperboreus, C. glacialis, C. finmarchicus, Pseudocalanus sp. and Oithona similis were investigated during June 2001 in Disko Bay, western Greenland. These 5 species dominated the zooplankton community in the upper 75 m, contributing 89 % of the total copepod biomass. Instantaneous mortality rates of copepodites of all 5 species and nauplii of Pseudocalanus sp. and O. similis were calculated using vertical life tables on abundances and published information on stage duration times. Compared with those covering a range of boreal habitats, the mortality rates were higher, with highest rates occurring in C. finmarchicus and C. glacialis copepodite stages I to III and Pseudocalanus spp. stage III (maximum = 0.18 d(-1)). Mortality rates remained lower in all stages of O. similis, When superimposing mortality rates for all species and stages on copepod size a significant peak at 1.3 mm prosome length was evident. This peak fitted a prey size dependent functional response of predation and the high mortality rates were, therefore, most probably attributable to size-specific predation.