TROPHODYNAMICS OF THE HYPERIID AMPHIPOD THEMISTO-GAUDICHAUDI IN THE SOUTH GEORGIA REGION DURING LATE AUSTRAL SUMMER

The feeding dynamics and predation impact of the hyperiid amphipod The misto gaudichaudi on mesozooplankton were studied in the vicinity of S outh Georgia, Southern Ocean, during austral summer 1994. Data show th at T. gaudichaudi is a visual opportunistic predator, consuming primar ily the most abundant species of copepods, euphausiids and pteropods. In situ estimated daily rations were equivalent to 6.3% of body dry we ight, and similar to the value of 7.1% of body dry weight derived usin g an energy budget approach which takes into account the total daily e nergy requirements. In vitro estimates produced daily rations higher t han these, ranging from 8.5 to 21.8% of body dry weight, increasing wi th prey density. The predation impact of T. gaudichaudi adults, averag ed over a 0 to 200 or 0 to 100 m layer, never exceeded 2.1% of mesozoo plankton standing stock per day but accounted for up to 70% of the dai ly secondary production. This suggests that in the vicinity of South G eorgia T. gaudichaudi adults are able to control the local mesozooplan kton community and may contribute significantly to the downward flux o f biogenic carbon.