Life history trends of copepods Drepanopus forcipatus (Clausocalanidae) and Calanus australis (Calanidae) in the southern Patagonian shelf (SW Atlantic)

Abstract

The copepods Drepanopus forcipatus and Calanus australis are key species in the mesozooplankton community over the southern Patagonian shelf. Their population abundance, stage composition and vertical distribution within the region were studied during late summer 2000. Individual size of adult females was also examined. Maximum abundances of D. forcipatus were recorded in outer waters of Grande Bay at ca. 51°S and decreased noticeably towards the northern and southern parts of the study area. Calanus australis was much less abundant but rather uniformly distributed over the entire study area. Highest numbers were recorded in the inner area of the Grande Bay and lowest in shelf waters offshore. Both populations were also differently distributed in the water column. Drepanopus forcipatus were concentrated mainly within the upper layers down to ca. 50 m, whereas C. australis were deeper close to the bottom. Late copepodids were dominant in both populations over most of the shelf. Size variation of adult females was much larger in D. forcipatus than in C. australis. Overall, these preliminary data suggest that both copepod species have developed different life-cycle strategies to contend with the suboptimal food conditions that typically follow the spring net-phytoplankton bloom in high latitude ecosystems. © The Author 2008. Published by Oxford University Press. All rights reserved.