Summer gregarine infection in Antarctic krill Euphausia superba in the Dumont D’Urville Sea,East Antarctic

Antarctic krill Euphausia superba plays a key role in the Antarctic food web.The trophic linkage between krill and other macro-organisms has been studied in the past decades,but the variability of parasites in krill is less studied and remains poorly understood.Therefore,it is important to understand the factors that influence abundance and infection of parasites in krill.Moreover,the relationship between the infection intensity of parasite and krill diet needs to be clarified,which is helpful for understanding the role of parasite in the food web.We investigated the abundance of the highly prevalent gregarine parasites in the digestive tract of krill and the factors influencing the gregarine infection to krill in the East Antarctic.The infection rate of Cephaloidophora pacifica Avdeev,1985 to krill(n=50 individuals)was 94%.The results of generalized linear model show the infection intensity of C.pacifica to the host was related significantly to the station,krill size,and maturity stage,but not the food species and abundance in the stomach of krill.Abundance of C.pacifica in krill differed among stations,and the lowest abundance occurred in the station nearest to the coast.Gregarines abundance varied among sexual maturity stages of krill and increased with krill size.

Distribution and abundance of euphausiid larvae and salps during austral summers in Prydz Bay,Antarctica

The distribution and abundance of euphausiid larvae and salps was studied from samples collected in 2002 and 2006 from Prydz Bay.Antarctica. Larvae of Thysanoessa macrura and Euphausia superba were mainly distributed in the north of the continental shelf.T.macrura was more abundant and had a relatively wider distribution.In 2006,with ice having retreated and higher seawater temperatures and chlorophyll a levels,E.superba and T.macrura occurred in higher abundances and at more mature developmental stages.Euphausia crystallorophias was mainly distributed in the neritic region.In 2002,with severe ice conditions in the neritic region,abundance of E.crystallorophias was only 95.6 ind·（1000 m）^（-3）.In 2006 when a polynya existed,the abundance of E.crystallorophias reached 43966.6 ind·（1000 m）^（-3）.The population mainly consisted of metanauplius（MN） and calyptopis I（CD.Salps,mostly Salpa thompsoni,had a low abundance in Prydz Bay.In 2002,S.thompsoni was only found at one station in the north of the bay with an abundance of 10 ind·（1000 m）^（-3）.In 2006,S.thompsoni was found at three stations located near the continental slope and average abundance reached 146.7 ind·（1000 m）^（-3）.Environmental factors,such as the timing of ice melt,polynya formation and food concentration appear to have a marked effect on the distribution and abundance of euphausiid larvae and salps.