Ecosystem Shifts in Arctic Seas

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In addition to the direct effects of sea ice loss on walrus (Odobenus rosmarus divergens) and polar bears (Ursus maritimus) that use ice as a platform, the decline of Arctic sea ice is predicted to promote a fundamental ecosystem shift from benthic animals that forage on the sea floor to pelagic animals that forage near the sea surface. 

An acetate peel image to count growth increments on a clam from the Chukchi Sea

Annual growth increments in an acetate peel of Serripes groenlandicus clam collected in the northeastern Chukchi Sea.
(Credit: Bryan Black, University of Texas, Marine Science Institute. Courtesy of Bryan Black, Limited Use by USGS Only)

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This shift would essentially result in Arctic seas transforming to ecosystems that resemble their temperate southern counterparts and raises concerns for walrus and eiders that are adapted to feed on the historically rich community of abundant benthic organisms.  As sea ice extent diminishes, more prolonged open-water phytoplankton blooms and increased zooplankton grazing may increasingly route surface primary production to pelagic consumers and away from the sea floor.  The change in benthic production has been difficult to quantify, leaving resource managers with much uncertainty.  We propose to relate annually resolved growth increments in benthic bivalves (clams) with satellite derived sea ice records to develop a predictive relationship between sea ice and benthic production in the Chukchi Sea.  Bivalve clams are a key prey item for both walrus and eiders.  The relative contributions of sea ice algae and phytoplankton, the two major sources of surface primary production, will also be described for bivalves using stable isotope analysis of soft tissue.  Combining these products with model projections of future sea ice cover will allow us to predict the pace of shifts in benthic production, clarify the underlying mechanism, and enhance forecasts of the population response of DOI managed species to a changing Arctic environment.

 

 

Biologists sorting through buckets of benthic invertebrates looking for bivalves onboard the Norseman II in the Chukchi Sea

Biologists sorting through buckets of benthic invertebrates looking for bivalves onboard the Norseman II in the Chukchi Sea.
(Public domain.)

Benthic invertebrates captured in a bottom trawl

Benthic invertebrates captured in a bottom trawl. 
(Credit: Jannelle Trowbridge, USGS. Public domain.)

Jannelle Trowbridge sorts through benthic invertebrates for bivalves

ANSEP intern, Jannelle Trowbridge, sorts through a catch of benthic invertebrates for bivalves on the Norseman II. 
(Credit: Vanessa von Biela, USGS. Public domain.)

 

2015 benthic field sampling team

The 2015 benthic field sampling team Jannelle Trowbridge, Vanessa von Biela, Carolynn Harris, and Thomas Nguyen. 
(Public domain.)

Identifying and sorting clams by species

Identifying and sorting clams by species. This sample came from benthic trawls on the Norseman II.
(Credit: Jannelle Trowbridge, USGS. Public domain.)

Sea ice in the Chukchi Sea

Sea ice in the Chukchi Sea.
(Credit: Jannelle Trowbridge, USGS. Public domain.)

Pacific walrus hauled out on sea ice in the Chukchi Sea

Pacific walrus hauled out on sea ice in the Chukchi Sea.
​​​​​​​(Credit: Tyrone Donnelly, USGS. Public domain.)