Spatial patterns in zooplankton communities and stable isotope ratios (δ13C and δ15N) in relation to oceanographic conditions in the sub-Arctic Pacific and western Arctic regions during the summer of 2008

Abstract

We define the biogeographic status quo of zooplankton communities sampled during the summer of 2008 in the sub-Arctic Pacific and western Arctic regions and examine spatial patterns of stable isotopes in the context of regional oceanography. Eight zooplankton assemblages were identified and corresponded to these regions: Gulf of Alaska, Bering Sea Slope, St-Lawrence Island, Western Bering Strait, Eastern Bering Strait, Barrow Canyon, Beaufort Gyre and Beaufort Shelf. Neocalanus spp., Eucalanus bungii and Metridia pacifica were abundant in the warmer and saltier waters of the Gulf of Alaska and on the Bering Sea Slope, whereas Calanus hyperboreus, Calanus glacialis and Metridia longa were abundant in the cold and fresher Arctic waters on the Beaufort Shelf and in the Beaufort Gyre. Salinity, nitrate and temperature, all of which were strongly correlated with latitude, and water column depth were the main factors influencing variation of zooplankton composition and spatial distribution. The δ15N values were less enriched in the Gulf of Alaska and on the Bering Sea Slope and more enriched in the eastern portion of Bering Strait and in Barrow Canyon. The δ13C values of zooplankton were more depleted in the Gulf of Alaska and in the Beaufort Sea regions and were more enriched in Western Bering Strait. The level of carnivory in the zooplankton community appeared highest in the Beaufort Gyre decreasing on the Beaufort Shelf and lowest in Western Bering Strait and in the Gulf of Alaska. Our results highlight the existence of large intra- and inter-specific differences in zooplankton isotopic signatures in relation to community composition and environmental conditions.