Interannual variations in euphausiid life stage distribution in the Dumont d'Urville Sea from 2004 to 2008

Euphausiid larvae were caught by oblique tows of a double-framed bongo net at 118 stations along the coast of Terre Adélie during every summer from 2004-2008. Larvae of Euphausia crystallorophias Holt and Tattersall and Thysanoessa macrura G.O. Sars were observed in the study area every year in contrast to larvae of Euphausia superba which were absent during the entire period of sampling. Highest abundances of both species were observed during the summer of 2005 and the lowest in the summer of 2004. Larvae of E. crystallorophias dominated every year and comprised more than 80% of the total abundance of euphausiid larvae. Within species, the calyptopis stages especially calyptopis 1 of E. crystallorophias dominated compared to furcilia stages of T. macrura which were less abundant. For both species, spatio-temporal variations in abundances of developmental stages were significantly correlated to density and salinity of the deep water layer. In the case of calyptopis 3 of E. crystallorophias, spatio-temporal variations were correlated with the number of days between the end of the sea ice retreat and the sampling day and for T. macrura inversely correlated to temperature of surface water layer. These variations are discussed and related to the timing of sea ice retreat, the sea ice concentration as well as metabolic conditions of adults of both species during their spawning period.