Seasonal variability of feeding and reproductive activity of the copepods Drepanopus forcipatus and Calanus australis in the Southern Patagonian Shelf: Post-bloom versus early- bloom conditions

ANTACLI, J.C.; SABATINI, M.E.; AKSELMAN, R.; HERNÁNDEZ, D.

Pucón

Simposio; 5to Simposion Internacional de Producción de Zooplancton; 2011

Center for Oceanographic Research in the Eastern South Pacific (COPAS), Universidad de Concepción, North Pacific Marine Science Organization (PICES), International Council for the Exploration of the Sea (ICES)

The copepods Drepanopus forcipatus and Calanus australis are key species in the plankton communities of the Southern Patagonian Shelf, together constituting most of the mesozooplankton biomass. However, their life strategies in relation to seasonal changes in food availability are poorly known. In late summer after the spring bloom, phytoplankton abundance has diminished and food availability in the size fraction mainly grazed by copepods (> 10 µm) is low, while in early spring food conditions are comparatively much less limited. This study compares the feeding and reproductive activities of both copepods during those two distinct food scenarios and examines the interactions between feeding and reproduction. To address this question, an index of feeding activity was measured, the gut contents were inspected, and the gonad stages were determined on the same specimens in both species. As expected, feeding and reproductive activity were markedly higher in early spring than in late summer for both species. Both copepods showed similar levels of feeding and reproduction in early spring, while during late summer feeding and reproduction were higher in Drepanopus forcipatus than in Calanus australis. The results will be discussed in relation to the particular strategies developed by these copepods to overcome food limitation (prey selection, compensatory feeding, diapause) and their effects on the life cycle and population dynamics.