MARKED INVERSE DISTRIBUTION OF SALPS TO OTHER MACROZOOPLANKTON IN WATERS ADJACENT TO THE SOUTH SHETLAND ISLANDS (15th Symposium on Polar Biology)

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Spatial distributions of salps and other zooplankton in the waters around the South Shetland Islands were examined. Two salp species, Salpa thompsoni and Ihlea racovitzai, were identified, and occurred with the latter more dominant than the former. At stations where salps dominated in terms of numerical abundance, other zooplankton were extremely scarce. Numerically, salps showed marked inverse distribution to copepods, amphipods, chaetognaths and polychaetes. This inverse distribution pattern covered the wide surface ranges of approximately 110 × 10^3 km^2. Its cause cannot be explained by either behavioral functions of organisms such as swarm formations or ecological regime such as interspecific exclusion. Predation by salps on zooplankton is also unlikely because only diatoms were found in the digestive tracts of salps. Salps inhabited waters with higher chl-a concentration than other zooplankton, and the contours of 0.3 mg・m^<-3> chl-a concentration corresponded roughly with the limit of salp distribution. This zonation by chl-a may be related to the distribution of Antarctic Winter Water (AWW), the subsurface temperature minimum. Higher chl-a together with low temperatures in the water column corresponded to the Antarctic Peninsula shelf water. Marked inverse distribution of salps and other zooplankton might be induced by an unknown function of the AWW.
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