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

Mortality rates of the copepodsCalanus hyperboreus,C. glacialis,C. finmarchicus,Pseudocalanussp. andOithona similiswere 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 ofPseudocalanussp. andO. similiswere 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 inC. finmarchicusandC. glacialiscopepodite stages I to III andPseudocalanusspp. stage III (maximum = 0.18 d–1).

Mortality rates remained lower in all stages ofO. 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.