ZOOPLANKTON AND LARVAL FISH COMMUNITY DEVELOPMENT: COMPARATIVE STUDY UNDER FIRST-YEAR SEA ICE AT LOW AND HIGH LATITUDES IN THE NORTHERN HEMISPHERE*

Abstract: We compared the development of the zooplankton community in relation to the ice-algal bloom in Saroma KO lagoon and Resolute Passage in spring. In Saroma KO, mysids and copepods were the dominant components of the zooplankton. Numerically, Pseudocalanus spp. represented more than 73% of the copepod assemblage. The constancy of Pseudocalanus stage composition and the low production of copepod eggs and nauplii indicated that ice algae in the lagoon did not stimulate the development of copepods in spring. During the sampling period, the colonization of Saroma KO by the larvae of several species of marine fish coincided with low production of zooplankton prey in the lagoon. In Resolute Passage, the hyperiid amphipod Themisto libellula and the copepod Pseudocalanus acuspes dominated the zooplankton. The population of Pseudo-calanus acuspes (78 % of the copepod assemblage) evolved from a majority of overwintering CIV and CV copepodites in early May to a majority of females in late June. The production of eggs and nauplii increased over this period and started well before the massive release of ice algae or the phytoplankton bloom. This suggests that Pseudocalanus acuspes reproduction may be fuelled by endogenous reserves from the previous fall and/or the grazing of ice algae falling from the ice-cover. Few fish larvae were sampled in Resolute Passage, indicat-ing that this area of strong advection is probably unsuitable for the reproduction of fish. Our results for Saroma Ko lagoon and Resolute Passage support the hypothesis that, in seasonally ice-covered seas, the importance of the ice-algal cycle to the maturation of Pseudocalanus increases with latitude. 1