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.