Zooplankton assemblages along the North American Arctic: Ecological connectivity shaped by ocean circulation and bathymetry from the Chukchi Sea to Labrador Sea

Abstract

We defined mesozooplankton biogeography in the North American Arctic to elucidate drivers of biodiversity, community structure, and biomass of this key component of the Arctic marine ecosystem. A multivariate analysis identified four mesozooplankton assemblages: Arctic-oceanic, Arctic-shelf, Coastal-Hudson, and Labrador Sea. Bathymetry was a major driver of the distribution of these assemblages. In shallow waters, Cirripedia and the copepod Pseudocalanus spp. dominated the Coastal-Hudson and Arctic-shelf assemblages, which showed low species richness (19) and biomass (0.28 and 1.49 g C m−2, respectively). The Arctic-oceanic assemblage occupied the entire North American Arctic, except for shallow breaks in the Canadian Arctic Archipelago downstream of sills blocking the Atlantic Water layer circulation below a depth of 200 m. This assemblage showed high copepod biomass (4.74 g C m−2) with a high share of Calanus hyperboreus, C. glacialis, and Metridia longa. In habitats below 200-m depth, C. hyperboreus represented 68% of the copepod biomass, underscoring its role as a keystone species in this ecosystem. Strong numerical representation by the boreal-Atlantic C. finmarchicus and Oithona atlantica stressed the strong Atlantic influence on the subarctic Labrador Sea assemblage on the northwestern Labrador Sea slope. The mixed Arctic-Atlantic composition of the Labrador Sea mesozooplankton resulted in high species richness (58) and biomass (5.73 g C m−2). The low abundance of Atlantic and Pacific taxa in the areas influenced by Arctic currents did not alter the Arctic status of the Arctic-oceanic, Arctic-shelf, and Coastal-Hudson assemblages. This study identifies hotspots of mesozooplankton biomass and diversity in Central Amundsen Gulf, Lancaster Sound, North Water Polynya and Baffin Bay, known for their high biological productivity and concentrations of vertebrate predators. The continental-scale zooplankton mapping furthers our understanding of the importance of bathymetry and ocean circulation for ecological connectivity in a vast and complex portion of the Arctic marine ecosystem.

Contrasting two major Arctic coastal polynyas: the role of sea ice in driving diel vertical migrations of zooplankton in the Laptev and Beaufort Seas

“…The zooplankton communities of the Beaufort Sea are characterized by different species composition and quantitative structure compared to the communities of the shallow Laptev Sea shelf. In contrast to the Laptev Sea, the larger-sized Arctic-oceanic taxa prevail in the Beaufort Sea (Darnis et al, 2014(Darnis et al, , 2022. Among them the most active diel migrators are the copepods Metridia longa, late copepodites of Calanus glacialis and chaetognaths Parasagitta elegans, all falling within the size range 2.0-20 mm, which is well detectable by acoustic backscatter.…”

“…In the Arctic Ocean, including its marginal seas, DVM are documented for several large-sized abundant Arctic copepods -Metridia longa, Calanus glacialis, smaller sized Pseudocalanus spp., mysids, and a chaethognath Parasagitta elegans (Runge and Ingram, 1991;Daase et al, 2008;Vestheim et al, 2013). Most of the listed species are inhabitants of relatively deep Arctic shelf regions with depths > 50 m (Conover and Huntley, 1991;Kosobokova et al, 1998;Darnis et al, 2022;Skjoldal and Aarflot, 2023). In the shallower regions, like the sites where regarded as migrators, but they are numerous in these regions only during the ice-free summer period (Abramova, 1999).…”