, Volume 41, Issue 1, pp 29-50
Date: 18 Nov 2010

Patterns of zooplankton diversity through the depths of the Arctic’s central basins

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Abstract

Metazoan zooplankton diversity is characterized for the oceanic environments of the Arctic Ocean, specifically the deep Nansen, Amundsen, Makarov and Canada Basins. Our species inventory is based on original records from 134 locations where stratified sampling of the entire water column was conducted from the surface to the bottom (or a maximum of 3,000 m) during seven icebreaker expeditions (RV Polarstern, 1993-2007, USCGC Healy, 2005) and two older expeditions of the Russian drifting ice stations North Pole 22 and 23 (1975-77). Representatives of eight large metazoan taxa, including Cnidaria, Ctenophora, Mollusca, Annelida, Nemertea, Crustacea, Chaetognatha, and Larvacea, all predominately oceanic species, are registered, with a total of 174 species. Crustaceans strongly dominate in terms of the species number (70%), and copepods are the most diverse group amongst them. Comparison with the historical data suggests that the composition of epi- and mesopelagic zooplankton is relatively well characterized to date, while a considerable number of species we encountered in the bathypelagic layers were either unrecorded before, or undescribed. There appears to be no zoogeographical barrier between the Eurasian and Canadian basins throughout the entire depth range. All deep-water and endemic species are found on both sides of the Lomonosov Ridge, suggesting effective exchange of the deep fauna across the ridge. Notable differences in the species composition in the upper and midwater layers are related to the occurrence of Atlantic and Pacific expatriates advected with their respective waters either into the Eastern or Western Arctic. A pronounced increase in Pielou’s evenness (J'), Shannon’s diversity (H'), and Margalef’s species richness (d) indices with depth, with a maximum occurring within the Atlantic layer, followed by a decrease in the deeper layers, was typical for all deep basins. Species-specific depth preferences and ranges result in statistically distinct communities at different depths with high within-depth similarity (60-80%). Differences were detectable between cruises in the epi- and mesopelagic layers (driven by the expatriates), but less so in the bathypelagic zone.