Life cycle strategy of the Antarctic calanoid copepod Stephos longipes

Studies on the life strategy of the small calanoid copepod Stephos longipes were carried out in the eastern Weddell Sea during four expeditions (January/February 1985, August 1986, October/December 1986 and April/May 1992). Samples were taken from the water column, the ice/water interface and the sea ice. In winter (August 1986) S. longipes copepodite stage CIV occurred mainly in the upper water layers of the ice covered eastern Weddell Sea, while only nauplii were found in the sea ice. In late winter/early spring (October-December 1986) very low numbers or S. longipes were found in the water column, mainly in the upper 50m, but high numbers occurred immediately below and within the sea ice. Adults dominated in the water column and in the under ice water layer while the sea ice contained nauplii and copepodite stage CI. During summer (January/February 1985) the eastern Weddell Sea was almost entirely free of ice with the exception of fast ice fields at the ice shelf. During this time S. longipes was concentrated in the upper 50m of the water column and in the ice/water interface where an ice cover was present. Young copepodite stages (CI-CIII) comprised the largest fraction of the population. In autumn (April/May 1992) as new ice began to develop, S. longipes, dominated by copepodite stage CIV, occurred in greatest number within mid-water layers. The abundance of S. longipes in autumn was similar to late winter/early spring highest in the sea ice and lowest in the water column. During all periods of investigation the population structure differed between the various habitats with the youngest population occurring in the sea ice and the oldest in the water column. A younger generation of the S. longipes population appears to overwinter in the sea ice and ice/water interface and an older one in deeper water layers or near the bottom.