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COMPETITION AMONG PENGUINS AND CETACEANS REVEALS TROPHIC CASCADES IN THE WESTERN ROSS SEA, ANTARCTICA

COMPETITION AMONG PENGUINS AND CETACEANS REVEALS TROPHIC CASCADES IN THE WESTERN ROSS SEA,... An apparent trophic cascade that appears during summer in the western Ross Sea, Antarctica, explains why the Antarctic silverfish ( Pleuragramma antarcticum ) there becomes cannibalistic; its principal prey, crystal krill ( Euphausia crystallorophias ) becomes scarce; and the diatom community is minimally grazed compared to adjacent areas. The krill is the major grazer of diatoms. On the basis of fieldwork at Ross Island, we suggest that the cascade results from foraging by unusually numerous Adéélie Penguins ( Pygoscelis adeliae ), minke whales ( Balaenoptera bonaerensis ), and fish-eating killer whales ( Orcinus orca ). These species and other top predators apparently deplete the krill and silverfish. In drawing our conclusions, we were aided by two ““natural experiments.”” In one ““experiment,”” large, grounded icebergs altered the seasonal pattern of change in regional sea-ice cover, but not the seasonal change in penguin diet and foraging behavior that was also detected during the pre-iceberg era. In the other ““experiment,”” a short-term polynya (opening in the ice) brought penguins and whales together in a confined area, this time altering both penguin diet and foraging behavior. We conclude that the foraging of penguins and whales, and not a formerly hypothesized seasonal decrease in sea-ice cover, explains (1) the annual switch in the penguins' prey from krill to silverfish, (2) the subsequent lengthening of penguin foraging trips, and (3) a marked decline of cetaceans in the area later in the season. Reduction in the middle-trophic-level prey is expressed in the relaxed grazing pressure on phytoplankton. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Ecology Ecological Society of America

COMPETITION AMONG PENGUINS AND CETACEANS REVEALS TROPHIC CASCADES IN THE WESTERN ROSS SEA, ANTARCTICA

Ainley, David G.; Ballard, Grant; Dugger, Katie M.
Ecology , Volume 87 (8) – Aug 1, 2006
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Publisher
Ecological Society of America
Copyright
Copyright © 2006 by the Ecological Society of America
Subject
Articles
ISSN
0012-9658
DOI
10.1890/0012-9658%282006%2987%5B2080:CAPACR%5D2.0.CO%3B2
Publisher site
See Article on Publisher Site

Abstract

An apparent trophic cascade that appears during summer in the western Ross Sea, Antarctica, explains why the Antarctic silverfish ( Pleuragramma antarcticum ) there becomes cannibalistic; its principal prey, crystal krill ( Euphausia crystallorophias ) becomes scarce; and the diatom community is minimally grazed compared to adjacent areas. The krill is the major grazer of diatoms. On the basis of fieldwork at Ross Island, we suggest that the cascade results from foraging by unusually numerous Adéélie Penguins ( Pygoscelis adeliae ), minke whales ( Balaenoptera bonaerensis ), and fish-eating killer whales ( Orcinus orca ). These species and other top predators apparently deplete the krill and silverfish. In drawing our conclusions, we were aided by two ““natural experiments.”” In one ““experiment,”” large, grounded icebergs altered the seasonal pattern of change in regional sea-ice cover, but not the seasonal change in penguin diet and foraging behavior that was also detected during the pre-iceberg era. In the other ““experiment,”” a short-term polynya (opening in the ice) brought penguins and whales together in a confined area, this time altering both penguin diet and foraging behavior. We conclude that the foraging of penguins and whales, and not a formerly hypothesized seasonal decrease in sea-ice cover, explains (1) the annual switch in the penguins' prey from krill to silverfish, (2) the subsequent lengthening of penguin foraging trips, and (3) a marked decline of cetaceans in the area later in the season. Reduction in the middle-trophic-level prey is expressed in the relaxed grazing pressure on phytoplankton.

Journal

Ecology – Ecological Society of America

Published: Aug 1, 2006

Keywords: Adéélie Penguin ; Antarctica ; Antarctic silverfish ; Antarctic toothfish ; crystal krill ; killer whale ; minke whale ; prey availability ; Ross Sea ; sea ice ; trophic cascade ; trophic competition

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