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Marine Ecology: Biological Responses to Changing Sea Ice
and Hydrographic Conditions in the Pacific Arctic Region

J. M. Grebmeier1, L. W. Cooper1, S. E. Moore2

1Chesapeake Biological Laboratory, University of Maryland Center
for Environmental Science, Solomons, Maryland, 20688 USA
2NOAA/Fisheries, Office of Science & Technology, Seattle, Washington, 98115 USA

November 21, 2011

Highlights

  • 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.
  • Changes in the distribution and biomass of some plankton and benthic prey are being observed in the Pacific Arctic with corresponding shifts in higher trophic predator feeding and migration patterns.

Seasonal sea ice duration and extent are critical factors driving biological processes and marine ecosystem structure. The seasonal ice zones have a direct influence on sea ice algal biomass and productivity and also provide early stabilization of the water column following sea ice melt, which can lead to intense phytoplankton blooms (see the essay on Arctic Ocean Primary Productivity). The timing and location of this primary production and associated grazing by zooplankton has a direct influence on the energy pathways connecting the water column to the underlying sediments. Recent studies indicate that increasing seawater temperature can have a positive impact on zooplankton growth rates (see the essay on Status and Trends of Benthic Organisms) and grazing rates. However, these changes will have the potential to diminish export production of carbon that currently supports globally significant soft-bottom infaunal populations on the shallow shelves of many areas of the Pacific Arctic (citations in Grebmeier et al. 2012). The short food chains characteristic of polar regions can have immediate cascading impacts on higher trophic organisms, including diving seaducks, seals, walruses, and whales. This is particularly the case when many of these apex predators require ice as a moving offshore feeding and resting platform that provides access to offshore foraging areas. In light of the changing dynamics of Arctic seasonal sea-ice (see the essay on Sea Ice), the marine ecosystems in polar regions will likely respond to both short-term population changes and long-term restructuring as sea ice retreat continues.

Some of the best-documented examples of biological response to physical forcing in the Pacific Arctic sector are prey-predator response to hydrographic shifts. For example, a reduction in sea ice provides access for seasonally-migrant baleen whales to feed north of Bering Strait (Moore and Huntington 2008). Gray whales now feeding north of the Bering Strait are likely responding to declines in benthic amphipod populations in the historical northern Bering Sea feeding grounds (citations in Grebmeier et al. 2012). Another change is in dominant clam populations in the northern Bering Sea, which have declined in abundance and biomass, as have Spectacled Eiders that preferentially consume these clams as prey. Modeling by Lovvorn et al. (2009) indicates that these diving birds lose more energy resting in the water between feeding bouts than when standing on ice. Thus, both the shift to more open-water conditions and the observed clam population declines are likely key factors creating energy stress for these diving seaducks. The recent observations of thousands of walrus coming ashore on both the US and Russia Chukchi coastlines are another indication of biological response to rapid sea ice retreat in the Chukchi Sea (see the essay on Biodiversity - Cetaceans and Pinnipeds). In addition to the increased mortalities for young walruses on beaches in close proximity to much larger adults, all of these shore-based populations have increased energetic requirements to access the productive offshore waters with higher benthic infaunal prey (citations in Grebmeier et al. 2012).

Over the last two decades specific marine sites have been occupied and re-occupied during both national and international ship-based projects. The data collected by these projects is forming a growing biologically-oriented time-series ranging geographically from the northern Bering Sea to Barrow Canyon. One of the most complete times-series is in the northern Bering Sea and includes sediment community oxygen consumption (Fig. ME6 upper panel), which is used as an indicator of carbon supply to the benthos. These data indicate a 30-50% decline over the last two decades coincident with ~30% decline in total infaunal biomass (Fig. ME6 lower panel). Other related evidence indicates a spatial shift northward in some fish distributions and marine mammal migrations, with direct impacts on habitat for ice-dependent species, such as walrus (citations in Grebmeier et al. 2012).

Fig. 6 -- Decline in sediment community oxygen consumption

Fig. ME6. Decline in sediment community oxygen consumption (SCOC; upper panel), which indicates a reduced carbon supply to the benthos and macroinfaunal biomass (lower panel) at sites southwest of St. Lawrence Island in the northern Bering Sea. Data updated from Grebmeier et al. 2006; red arrow indicates the start of those new data. Most benthic data illustrated are available at: http://www.eol.ucar.edu/projects/sbi (phase I, Dunton, Grebmeier & Maidment component; and phase II, Grebmeier & Cooper component) and http://www.eol.ucar.edu/projects/best (Grebmeier & Cooper component).

The biological response to sea ice retreat and environmental change is being tracked through coordination among scientists in the Pacific Arctic Group (http://pag.arcticportal.org/). This voluntary international interest and working group has initiated a "Distributed Biological Observatory (DBO)" that includes select biological measurements of lower trophic level species that are tied to higher trophic level species, as well as undertaking coordinated hydrographic measurements. The DBO is developing as a change detection array for the identification and consistent monitoring of biophysical responses. Data sets from 2010-2011 pilot studies, along with other biological time series results, and information are available at http://www.arctic.noaa.gov/dbo/. Efforts are also underway to network the DBO with biological observatories in the Eurasian Arctic, e.g., the "HAUSGARTEN" deep water biological observatory, and developing transect-based biodiversity sampling on behalf of the CBMP (Circumpolar Biodiversity Monitoring Program) of the Arctic Council (http://caff.is/monitoring).

References

Grebmeier, J. M. 2012: Shifting patterns of life in the Pacific Arctic and Sub-Arctic seas. Ann. Rev. Mar. Sci., 4: 16.1-16.16 (in press, doi: 10.1146/annurev-marine-120710-100926).

Grebmeier, J. M, J. E. Overland, S. E. Moore, E. V. Farley, E. C. Carmack, L. W. Cooper, K. E. Frey, J. H. Helle, F. A. McLaughlin, and L. McNutt, 2006b: A major ecosystem shift in the northern Bering Sea. Science, 311: 1461-1464.

Lovvorn, J. R., J.M. Grebmeier, L.W. Cooper, J.K. Bump, and J.G. Richman, 2009: Modeling marine protected areas for threatened eiders in a climatically shifting Bering Sea, Ecol. Applic., 19(6), 1596-1613.

Moore, S.E. and H.P. Huntington. 2008. Arctic marine mammals and climate change: impacts and resilience. Ecological Applications 18(2): S157-S165.