| Summary: | The ongoing temperature increase in the Arctic affects the succession patterns in the marine pelagic ecosystem. Reduction and earlier breakup of sea ice changes the initiation of the spring bloom. Along the Greenland coast three species of Calanus dominate the zooplankton; C. hyperboreus, C. glacialis and C. finmarchicus. C. hyperboreus and C. glacialis are large lipid rich Arctic species, whereas C. finmarchicus is a smaller North Atlantic species. During the last two decades we have investigated the Calanus community in the Disko Bay, western Greenland. Calanus are impacted by the environmental changes, directly through their physiological rates as egg production, development, growth, and metabolic cost and indirectly via the environment through changes in ice cover, salinity, and food availability. The Calanus species have different lifecycles and show different responses to increasing temperatures. The aim of this talk is to discuss possible effects of climate change on coexisting Calanus species. Our result from in situ and laboratory studies illustrates that Calanus in Disko Bay are well adapted to Arctic conditions with unpredictable pulses of food. All three species continue reproduction when starved. Pre-feeding history of C. glacialis and C. finmarchicus are important to the starvation response as it affects gonad maturation. Only C. finmarchicus that have previously fed will continue egg production during starvation, unlike C. glacialis that sustain egg production without food. This advantage however diminishes with increasing temperature. At temperatures above 5 °C both starved and fed C. finmarchicus can produce egg at a rate similar to C. glacialis. The reproduction by the winter spawner C. hyperboreus seemed to be endogenously controlled, as neither food nor temperature affect reproductive output. The eggs of C. hyperboreus develop relatively fast at low temperature, and nauplii can survive long periods of starvation
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