Ecology of tropical hermit crabs at Quirimba Island, Mozambique: shell characteristics and utilisation

The use of gastropod shells by hermit crabs at Quirimba Island, Mozambique, was investigated. Particular attention was paid to the upper shore/supralittoral zone species Clibanarius longitarsus, Coenobita cavipes and Coenobita rugosus. The study area is characterised by a high diversity of gastropod species as well as hermit crabs. Supralittoral hermit crabs were little, if at all, resource restricted due to concentration of empty shells on the strandline and shell middens created by local people. The range of the 3 study species overlaps substantially and each uses a wide range of shell types. Shore habitat, shell abundance and availability were found to have little influence on shell use. With increased tidal emersion/terrestrial nature (for a given crab mass), total diversity of shells used increased, shell mass carried decreased, damaged shell use decreased and carried shell fit increased. The architecture and strength of shells used, however, followed more complex individual species characteristics and behaviour patterns. Species specific differences in behavioural patterns may be important for shell resource partitioning.