Mesozooplankton dynamics in relation to food availability during spring and early summer in a high latitude glaciated fjord (Kongsfjorden), with focus on Calanus

The timing of zooplankton reproduction in relation to spring pelagic bloom is essential in determining grazers' recruitment success and the transport of biomass through the system. At high latitudes marine ecosystems are characterized by extreme seasonality with the production of autotrophes concentrated during the spring. In two consecutive years we studied mesozooplankton during spring and early summer in Kongsfjorden, Svalbard (79°N), aiming at identifying the main grazers and understanding what affects the timing in zooplankton. The main grazers were females and nauplii of holoplanktonic Calanus, together with meroplanktonic Cirripedia nauplii and Polychaeta larvae. The appearing of offspring and larvae showed a correlation with the spring bloom which occurred earlier in 2004 compared to 2003. The Arctic Calanus glacialis reproduced before its Atlantic counterpart Calanus finmarchicus and prior to the bloom. In the Arctic regions decreasing sea ice cover as a result of climate change is expected to alter the timing of the spring bloom which in turn will pose a need for the zooplankton to adjust their reproduction activities. Subsequently, this adjustment will influence ecosystem functioning mainly by modifying particulate organic matter and energy fluxes.

► Zooplankton development during spring in Arctic fjord with high temporal resolution.
► Zooplankton reproduction is well synchronized with spring bloom.
► Meroplanktonic larval stages of benthic species are important grazers of the bloom.
► Calanus glacialis reproduces earlier than Calanus finmarchicus.