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Marine Ecosystems Summary
Section Coordinators: Sue Moore1 and Mike Gill2
1NOAA Fisheries Office of Science and Technology,
Marine Ecosystems Division, Seattle, WA, USA
2Canadian Wildlife Service, Environment Canada, Whitehorse, YT, Canada &
Conservation of Arctic Flora and Fauna (CAFF)/Circumpolar Biodiversity Monitoring Programme
November 7, 2011
The Marine Ecosystem section of the 2012 Arctic Report Card highlights the highly variable nature of Arctic ecosystems and provides some insight into how the marine ecosystem and the biodiversity it supports are responding to changing environmental conditions. Recent changes in the marine ecosystem, from primary and secondary productivity to responses by some marine mammals species, are summarized in six essays. These essays provide a glimpse of what can only be described as profound, continuing changes in the Arctic marine ecosystem. For example, primary production by phytoplankton in the Arctic Ocean increased ~20% between 1998 and 2009, mainly as a result of increasing open water extent and duration of the open water season (see the essay on Sea Ice). Increases in primary production were geographically heterogeneous, with greatest increases found in the Kara (+70%) and Siberian (+135%) sectors. In addition to shifts in the total amount of production, recent observations indicate an earlier timing of phytoplankton blooms in the Arctic Ocean (advancing up to 50 days over the period 1997-2009), as well as community composition shifts towards a dominance of smaller phytoplankton species. These changes in production were accompanied by biogeochemical shifts in the system, including profound freshening of waters in the Canadian Basin (see the essay on Ocean Temperature and Salinity) and an undersaturation of the surface waters with respect to aragonite, a relatively soluble form of calcium carbonate found in plankton and invertebrates (see the essays on Ocean Biogeophysical Conditions and Ocean Acidification).
Shifts in primary and secondary production have direct impacts on benthic communities. Organic carbon supply to the benthos in regions of the northern Bering Sea has declined ~30-50%, as has the infaunal biomass of bivalves that are winter prey for the World population of the threatened spectacled eider. Recent changes in Arctic benthic biodiversity include shifts in community composition and biomass, which might be related to climate warming. In several cases, switches from longer-lived and slow-growing Arctic species and/or communities to faster-growing temperate species and/or communities reflect increasing water temperatures. Similarly, northern range extensions of several sea floor dwellers likely are tied to the warming habitat. In the Atlantic Arctic, this process is anticipated to result in the 'Atlantification' of the benthos, i.e., the replacement of Arctic communities with those endemic to the North Atlantic Ocean. New research on sediment-associated microbes, including bacteria, archaea, viruses and microscopic fungi, are currently expanding our knowledge of this topic.
Changes in the Marine Ecosystem are affecting higher-trophic species including seabirds and marine mammals. For example, 7 of 19 of the world's polar bear sub-populations are declining in number, with trends in two populations linked to reductions in sea ice. Thousands of walruses had hauled out on the NW coast of Alaska by mid-August 2011, the fourth time in the past five years for a behavior thought to be triggered by a lack of sea ice in the Chukchi Sea (see the essay on Sea Ice). These unprecedented haul-outs result in pup mortality by crushing and a switch in foraging by walrus from moving sea ice to static shore sites. Conversely, the decline in sea ice extends access to waters north of Bering Strait for feeding by seasonally-migrant baleen whales. Sea ice reductions in the Northwest Passage also provided the opportunity for overlap between bowhead whales from the West Greenland and the Alaska populations, suggesting that reduced summer sea ice may facilitate exchange between the two populations.
Photograph of fieldwork on the US Coast Guard Cutter Healy in June-July 2010 in the Chukchi Sea as part of the NASA ICESCAPE mission. Courtesy of Karen Frey.
