Condition of Euphausia crystallorophias off East Antarctica in winter in comparison to other seasons


S. Nicol, P. Virtue, R. King, S.R. Davenport, A.F. McGaffin, P. Nichols


Antarctic coastal krill  (Euphausia crystallorophias) were collected in Austral winter (July/August) 1999 in the Mertz Glacier polynya off the coast of East Antarctica and were compared to krill collected off East Antarctica during summer in 1996 and 2001 and spring 1999.  A range of experiments and measurements were conducted to assess their relative condition in winter and summer.  Krill collected in winter had light green digestive glands indicating some recent feeding activity; however, the size of the digestive glands was small relative to the size of glands of krill of the same size caught in summer.  This indicates that feeding had been occurring only at low levels during the collection period.  Growth rates, measured using the instantaneous growth rate methodology on live adults, were close to zero in winter indicating that some food had been available during the period of the moult cycle. Growth rates in summer ranged from 3-8% per moult cycle. The mean length of the moult cycle was significantly greater than the measured intermoult period in summer. Lipid levels were low in winter, less than 5% of body weight compared to summer levels of ~15%. Winter krill were richer in wax esters and poorer in polar lipids than specimens collected in summer. Krill in winter were lacking in C16 PUFAs that are markers of a phytoplankton diet which are common in summer and had significantly higher levels of 20:1 and 22:1 fatty acids (2.3%)and alcohols (8.1%) than krill sampled in summer (0.2%, 0%) indicating a shift to a carnivorous diet.


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