FORAGING ACTIVITIES OF CHILEAN INTERTIDAL CRABS ACANTHOCYCLUS-GAYI MILNE-EDWARDS ET LUCAS AND ACANTHOCYCLUS-HASSLERI RATHBUN
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1988
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Foraging activities of the Chilean intertidal carnivorous crabs Acanthocyclus gayi Milne-Edwards et Lucas and A. hassleri Rathbun were studied in the laboratory. These crabs are morphologically similar and coexist in the intertidal zone, feeding mainly on mussels, barnacles, and gastropods. The consumption rates of A. gayi were generally higher than those of A. hassleri, when feeding on mussels and limpets, but similar, when feeding on barnacles. Both species foraged more actively underwater. Out of water, foraging activity was greater at night than during the day. Both crab species preferred the smallest sizes of the mussel Perumytilus purpuratus Lamarck, well below the maximum size they can handle. In both species, the critical size of mussels increased linearly with crab size. A. hassleri was able to handle larger mussels than its congenergic species, but when > 15 mm carapace width both crabs could handle even the largest mussels found in the field. A. gayi strongly preferred the mussel Semimytilus algosus (Gould), which is much less abundant in the intertidal than P. purpuratus, and the least preferred item was the barnacle Jehlius cirratus (Darwin), one of the most abundant organisms in the field. In paired experiments, A. hassleri showed the same preference order as A. gayi, and when all prey species were available, A. hassleri preferred J. cirratus over any other prey. Both crabs used similar techniques to handle, open, and eat their prey. Crabs adopted any of six different techniques to handle mussels, depending largely on the crab-prey size ratio. For handling limpets and barnacles, the crabs used two different techniques, which also depended on crab and prey sizes. In conclusion, the two crab species are similar, not only morphologically, but also in their trophic behaviour. Factors enabling the coexistence of both species in the intertidal zone need further study. The results are compared with those obtained for other crab species and the possible ecological role of Chilean crabs in the community is discussed.