Climate-induced variability in Calanus marshallae populations

Calanus marshallae is the dominant mesozooplankton copepod species over the south-eastern Bering Sea middle shelf. Climate-induced changes in the magnitude and timing of production by C. marshallae may affect the living marine resources of the Bering Sea shelf ecosystem. We examined springtime abundance, gonadal maturity and stage distributions of C. marshallae copepodites during five consecutive years (1995-1999) that spanned the range of variability observed over the past 34 years in terms of water temperature and ice cover. We compared our results with previous work conducted during cool (1980) and warm (1981) years [Smith, S. L. and Vidal, J. (1986) Cont. Shelf Res., 5, 215-239]. The spring phytoplankton bloom began relatively early in association with ice (1995, 1997, 1999), but began late when ice was absent or retreated early (1996, 1998). Egg production began well before the bloom and continued over a long duration. Copepodites, however, were recruited during a relatively short period, coincident with the spring phytoplankton bloom. The relationship between brood stock and spring-generation copepodite abundances was weak. Copepodite concentrations during May were greatest in years of most southerly ice extent. Copepodite populations were highly variable among years, reflecting interannual variability in the atmosphere-ice-ocean system.