Female and young walruses depend on disappearing Arctic sea ice for food sources

Date:
August 20, 2021
Source:
University of Maryland Center for Environmental Science
Summary:
A new study shows that disappearing sea ice is a significant
element of the food web supporting female walruses and their
dependent young in the Arctic's Chukchi Sea. Researchers were able
to trace biomarkers that are unique to algae growing within sea
ice to connect marine mammals with a food source that is rapidly
diminishing in the face of climate change.



FULL STORY ==========================================================================
A new study shows that disappearing sea ice is a significant element of
the food web supporting female walruses and their dependent young in the Arctic's Chukchi Sea. Researchers were able to trace biomarkers that are
unique to algae growing within sea ice to connect marine mammals with
a food source that is rapidly diminishing in the face of climate change.


========================================================================== "This study builds on work we have been doing in the Bering and Chukchi
Seas to show that these tracers of ice algae and phytoplankton can be
used to monitor the ecosystem response to disappearing sea ice," said
lead study author Chelsea Koch of the University of Maryland Center for Environmental Science." "Ongoing monitoring of these sea ice biomarkers
in walruses and even other organism tissues in the region will potentially
help us to identify how the system is responding to changing food sources
at the base of the food web as a result of climate change." The marine ecosystem of the Pacific Arctic near Alaska is adapted to utilizing
fat-rich foods derived from biological production in sea ice. Ice algae
blooms lead to a pulse of high-quality food to the sea floor. This in turn supports high abundances of clams and other benthic organisms throughout
the Bering and Chukchi Seas -- and lots of food for walruses to eat.

However, the loss of seasonal sea ice poses a threat to Pacific walruses, particularly how they use sea ice for rest and to access and forage on
these dense offshore clam beds. With the disappearance of sea ice in
many recent years near Alaska, thousands of walruses are coming ashore
on coastal beaches in the late summer that are distant from the most
productive clam beds.

Stampedes are also likely to occur with these massive gatherings,
leading to additional mortalities.

Based on the migration patterns of adult females and juveniles moving
north with the ice edge each spring, Koch and the research team expected
to see higher signatures of ice algae in the walruses harvested from
the Chukchi Sea.

However, results from the northern Bering Sea revealed a more nuanced
finding, aligning with the traditional local knowledge of subsistence
hunters on St.

Lawrence Island.

Walruses were evaluated for Endangered Species Act listing due to the
decline of seasonal sea ice in the Arctic. They are also important in
some Alaska Indigenous communities as a source of subsistence food.

"One of the interesting findings was that these sea ice biomarkers were consistently higher in the female walruses in the northern Bering Sea
compared to the males. These markers are short-lived in walrus livers,
on the order of days or maybe weeks. So we know this elevated sea ice
signature in the females is not an accumulation from their previous years' journey into the Chukchi Sea," said Koch. Researchers were able to trace biomarkers using liver tissues from some animals that were harvested as
part of subsistence hunting.

This provides supporting evidence that female foraging behavior differs
from the males in the winter and spring months while in the Bering Sea.

The work was carried out in coordination with a number of partners
in Alaska and also included scientists from Clark University and the
Scottish Association for Marine Science. Samples from the Bering Sea were provided by the University of Alaska's Museum of the North, who in turn received the samples as donations from subsistence hunters. Samples from
the Chukchi Sea were collected by the North Slope Borough Department of Wildlife Management (NSB DWM) as part of their harvest and walrus health harvest monitoring program. Co-author Dr.

Raphaela Stimmelmayr of the NSB DWM emphasized that "without
the support of the hunters of regional community-based harvest
monitoring programs, important studies like this would not be possible." ========================================================================== Story Source: Materials provided by University_of_Maryland_Center_for_Environmental_Science.

Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Chelsea W. Koch, Lee W. Cooper, Ryan J. Woodland, Jacqueline M.

Grebmeier, Karen E. Frey, Raphaela Stimmelmayr, Ce'dric Magen,
Thomas A.

Brown. Female Pacific walruses (Odobenus rosmarus divergens)
show greater partitioning of sea ice organic carbon than males:
Evidence from ice algae trophic markers. PLOS ONE, 2021; 16 (8):
e0255686 DOI: 10.1371/ journal.pone.0255686 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/08/210820111104.htm

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