Biogeography of epibenthic assemblages in the central Beaufort Sea

Abstract

Benthic communities change drastically in both biomass and community structure with increasing water depth on a global scale, attributed to a combination of food supply, environmental drivers, as well as physiological and competitive capacities. In the Arctic, benthic biogeographic patterns are additionally thought to be a result of the region's glaciation history. Here, we investigate gross epibenthic biomass and assemblage structure turnover with water mass from coastal to bathyal depths from 136 beam trawl samples collected in the Beaufort Sea. We test whether Pacific Boreal Arctic species have their core distribution in shelf water masses while Atlantic Boreal Arctic species have wider depth ranges. Gross biomass estimates differed statistically among water masses, with high values mostly under the influences of the Polar Mixed Layer and Arctic Halocline (outer shelf and upper slope, respectively). Stations in the Coastal Zone and Canada Basin Deep Water had the lowest biomass. Epibenthic assemblages also differed significantly among water masses, with high taxon richness in shelf water masses that decreased considerably with depth. Biomass of benthic taxa with Pacific Boreal Arctic affinity was essentially limited to the shelf, while Atlantic Boreal Arctic taxa occurred across a broad depth range, though their biomass increased in deeper water masses for mollusks and echinoderms, but not for decapods/isopods. Our results confirm earlier evidence of a strong Atlantic-Arctic deep-water connectivity reaching into the Pacific Arctic region and suggest new arrivals of species from the boreal Pacific are likely to settle on Pacific Arctic shelves, but are unlikely to invade continental slope and basin waters in the foreseeable future.

Epibenthic megafauna communities in Northeast Greenland vary across coastal, continental shelf and slope habitats

“…Such a shift was for example seen in the abrupt appearance of the deep-dwelling glass shrimp Pasiphaea tarda beyond the shelf break. Also, the ophiuroid Ophiopleura borealis was absent from the slope but abundant on the shelf in the present study, though this distribution pattern appears to contradict Piepenburg et al (1997b) and Ravelo et al (2015Ravelo et al ( , 2020 who found that O. borealis was absent from the shelf but present on the slope near our study area and in the Beaufort Sea, respectively.…”

“…While the three slope locations were geographically far apart, their communities were rather similar, with relatively similar depth and hydrography (Table 7), a finding similar to slope communities along the Arctic interior Beaufort Sea (Ravelo et al 2020). Abundances were also similarly low at these slope locations, consistent with the decreasing amount of food particles that reach the seabed with increasing depth (Riser et al 2008) in the study area.…”

“…In fact, drop stones have even been observed at depths > 1000 m in the Fram Strait and the Canada Basin (MacDonald et al 2010;Taylor et al 2016;Zhulay et al 2019). In those studies and at various shelf breaks the increased heterogeneity also increased taxon richness on a local scale (Mayer and Piepenburg 1996;Buhl-Mortensen et al 2012;Ravelo et al 2015Ravelo et al , 2020, but the shelf break stations in the present study in fact exhibited the lowest taxon richness. The cause is unclear, though poorer performance of our trawl on the uneven seabed topography might be a contributing factor.…”

“…At continental slopes, epibenthic community changes are particularly evident because depth increases quickly over short geographic distances (Mayer and Piepenburg 1996;Buhl-Mortensen et al 2012). This strong community shift with depth was reflected in the high dissimilarity of slope and shelf communities also found at other slopes (Buhl-Mortensen et al 2012;Ravelo et al 2020). Such a shift was for example seen in the abrupt appearance of the deep-dwelling glass shrimp Pasiphaea tarda beyond the shelf break.…”

Borealization of the Arctic Ocean in Response to Anomalous Advection From Sub-Arctic Seas

“…Shifts in relative dominance of certain indicator species (in this case two brittle star species) in the Alaskan Beaufort Sea between the 1970s and 2010s were also thought to be related to the strength of the boundary current, a transport pathway of pelagic larvae for the species more common in the CS (Ravelo et al, 2015). Whether any of these benthic shifts would perpetuate into the basin is doubtful given Pacific-affinity species are virtually absent in deep slope and basin areas of the CS and BG margins today and seem to have limited depth tolerance (Zhulay et al, 2019;Ravelo et al, 2020). As with holozooplankton, range expansions of largely immobile benthic animals are limited by residence time of their pelagic larvae on the CS shelf.…”