THE LIFE-CYCLE OF STEPHOS-LONGIPES - AN EXAMPLE FOR CRYOPELAGIC COUPLING IN THE WEDDELL SEA (ANTARCTICA)

Distribution, abundance and age composition of the calanoid copepod Stephos longipes (Giesbrecht) were studied in the southeastern Weddell Sea in January-February 1991. Samples were taken in the water column with a multiple closing net in 5 depth strata down to 1000 m. Concurrent samples were taken from drifting ice floes and from a 1 m deep layer underneath the pack ice (under ice water layer: UIWL) using a specially designed pump. S. longipes was the predominant calanoid copepod at most stations throughout the continental shelf area within the upper 50 m of the water column. Generally, abundances inside the pack ice floes exceeded those in the UIWL by 1 to 3 orders and the water column below by 3 to 5 orders of magnitude respectively. The mean population stage was lowest inside the ice floes followed by the UIWL and the water column. Also, nauplii and young copepodite stages (CI and CII) often outnumbered all other metazoan groups within and beneath the ice. Highest densities of S. longipes (> 90 000 M-3) were observed in ice floes and UIWL samples where platelet ice was particularly frequent, probably as a result of the extreme stickiness of S. longipes eggs and their attachment to floating ice crystals. Fecal pellets of S. longipes, collected in the UIWL, were in most cases filled with sea ice algae. Our results indicate that the life cycle of S. longipes is closely associated with the sea ice, especially platelet ice layers, where a high algal standing crop can sustain a sufficiently high secondary production in an otherwise food limited habitat. Thus, S. longipes uses a completely different strategy than large calanoid copepods in the Antarctic which do not inhabit sea ice at any given time during their life cycle.