Growth and behavior of larval krill (Euphausia superba) under the ice in late
winter 2001 west of the Antarctic Peninsula
Robin M. Ross1, Langdon B. Quetin1,
Timothy Newberger2 and Stephanie A. Oakes1
1 Marine Science Institute, University of
California at Santa Barbara, Santa Barbara, CA 93106
2 Lamont-Doherty Earth Observatory, Columbia
University, Palisades, NY 10964
In
situ growth rates are one measure of the physiological condition of larval
Antarctic krill in winter. During the
Southern Ocean Global Ecosystem Dynamics research cruise in July/August 2001
aboard the ARSV LM Gould west of
Adelaide Island and Marguerite Bay, larval krill were observed in the under-ice
habitat. Ten instantaneous growth rate
experiments were conducted with larvae collected from the under-ice habitat on
the outer shelf, mid-shelf and just south of Adelaide Island in the mouth of
Marguerite Bay. Larvae were observed
feeding on the ice, even though no color was visible. Pigment (chlorophyll a) content of larvae
from three of the sites was measured as an indicator of ingestion of plant
material. For all experiments, larvae
average growth increments of ~ -1.6% per intermolt
period, and a median intermolt period of 30.6 d. Pigment values were near values found in
starved controls. The data indicate the
larvae were feeding at low rates and thus were shrinking. These results were compared to growth rates
of larvae during 9 previous winter cruises that covered all months except for
August, and yielded a pattern of growth that decreased to a low in mid- and
late winter, increasingly sharply by September.
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