Abstract

Large-sized octopus species are known to be generalist predators. In this study we examined experimentally the prey selection of Octopus tehuelchus d'Orbigny, a small-sized species, and concluded that it consumes only a small set of the potential prey species available in San Antonio Bay (40-degrees 45' S, Argentina), and that feeding rate varies according to prey species. The oysters Ostrea puelchana d'Orbigny and 0. equestris Say were never attacked. Brachidontes rodriguezi (d'Orbigny), a small mussel, was mostly attacked when it was the only available prey, but at a low rate. Among subtidal crabs species, Corystoides chilensis Milne-Edwards and Rochinia gracilipes Milne-Edwards were preferred to Leurocyclus tuberculosus (Milne-Edwards & Lucas), Libinia spinosa Milne-Edwards, and Pilumnus reticulatus Stimpson, which were only partially consumed, and these to Ebalia rotundata Milne-Edwards, which was never attacked. Octopus tehuelchus is largely allotopic with Chasmagnathus granulata Data and syntopic with Cyrtograpsus angulatus Dana (both intertidal grapsid crabs); while Chasmagnathus was always attacked and eaten immediately, Cyrtograpsus was never attacked, even after prolonged periods of starvation. The number of attacks on Chasmagnathus diminished when Cyrtograpsus was present. The presence of chemical attractants and/or deterrents may explain prey ranking among some crab species.