A 12-year study of the seasonal and interannual dynamics of mesozooplankton in the Laptev Sea: Significance of salinity regime and life cycle patterns

Abstract

Over a 12-year period (1989–2000) the spatial and temporal distribution of zooplankton in the Laptev Sea (Arctic Siberia) has been investigated. A total number of 111 taxa from 10 phyla were found. Sixteen species are reported from this region for the first time. The distribution and abundance of zooplankton on the Laptev Sea shelf is dependent on the main direction of river water spread, which varies between years. While the western and northeastern Laptev Sea shelf is dominated by a marine–neritic fauna, the central part is inhabited by a transitional brackish–marine assemblage. A brackish–neritic community characterizes the eastern and southeastern regions, where lowest salinities usually prevail. Closer to estuaries the summer zooplankton consists of both freshwater and brackish-water species, whereas in winter brackish-water species are dominant. Average zooplankton abundance varies seasonally and interannually, particularly in the southeastern Laptev Sea. The amplitude of these variations mainly depends on the state of the populations of the most common Copepoda species, the intensity of their reproduction, and their success in overwintering. Two seasonal abundance maxima were found, at the end of winter and at the end of summer. During the period of highest reproduction in summer the abundance may be 50 times greater than during overwintering. The average population abundance can vary by the factor of 2 in summer and in winter from year to year.