Early reproduction by Calanus glacialis in the Northern Bering Sea: the role of ice algae as revealed by molecular analysis

Calanus glacialis initiated feeding and reproduction under extensive sea ice in the northern Bering Sea during late winter despite very low mean water column chlorophyll a concentrations. A peptide nucleic acid (PNA)-PCR and clone library analysis of prey 18S rDNA in the guts of C. glacialis, together with the quantification of the more abundant prey species with quantitative PCR (qPCR), demonstrated feeding on sea ice algae. The ice algal diatoms, Fragilariopsis cylindrus, Fragilaria sp. and Pseudonitzschia sp. were the dominant prey species while the most abundant species in the water column, Thalassiosira antarctica, was not important. The total of these species-specific ingestion rates was strongly correlated (r(2) = 0.93) with, and similar to, those estimated from gut pigments. The increase in feeding and reproduction during the study was significantly related to air temperature lagged by 2 or 3 days. We suggest that warmer temperatures led to a release of ice algae into the water column stimulating feeding and reproduction. The availability of ice algae over an extended period during colder winters when sea ice cover is more extensive and lasts longer will lead to larger population sizes of C. glacialis compared with warmer years with less extensive ice cover.