Diversity and vertical distribution of mesozooplankton in the Arcticʹs Canada Basin

The composition and biomass of the zooplankton community within the Canada Basin down to 3000 m was studied during July 2005 at 12 stations. A total of 111 species including 74 species of crustaceans (55 species of copepods, 2 euphausiids, 11 amphipods, 1 decapod, 5 ostracods), 17 cnidarians (12 hydromedusae, 1 scyphomedusae, 4 siphonophora), 1 foraminifera, 4 ctenophores, 2 pteropods, 4 larvaceans, 4 chaetognaths, and 5 polychaetes were identified. Most of the species observed are typical of the Arctic waters, with the notable exception of several Pacific expatriate copepod species, suggesting no zoogeographical barrier between the Canadian and Eurasian basins. Overall species inventories appear unchanged over the past 50 years, and were similar to the Eurasian Basins. Zooplankton biomass averaged 3.6±0.23 g DW m−2, with ∼50% of the biomass concentrated within the upper 100 m; nonetheless significant biomass and the majority of species diversity occurred below 100 m. Copepods represented 91% of the community numerically, followed by pteropods (2.6%), larvacean (1.8%) and shelled protists (1.5%), with other groups each contributing 1% or less. While copepods represented 85% of the total biomass, chaetognaths represented 13% on average (ca. 50% of non-copepod biomass), followed by cnidarians plus ctenophores (4.6%), ostracods (3.6%), and other groups (∼2% or less). Species-specific depth preferences and ranges resulted in statistically distinct communities in different depth strata and showed an orderly departure in similarity with increasing distance between strata. In Arctic waters, because temperature varies relatively little over the water column, so should respiratory rates; hence deep-water species are likely to play a greater role in the transfer or recycling of surface production than is typical of other deep ocean communities.