Upwelling-generated plankton strandlines: important predictable food sources for seabirds at Husvik,South Georgia

Sustained strong offshore winds generate upwelling in the fjords of northern South Georgia. Deepwater plankton is pumped by upwelling towards sandy beaches at the heads of the fjords; calanoid copepods, chaetognaths and pteropods are stranded by the sand filter in large quantities on falling tides. Local benthonic species (harpacticoid copepods and amphipods) are present in the plankton but do not strand. Strandlines are very rich (<4 kg wet mass m^-2) and provide large fractions of the food of kelp gulls, sheathbills and terns in the austral summer. Birds can only exploit fresh strandlines, since air-drying of the plankton soon makes it too salty to eat.