MOVEMENT, ACTIVITY PATTERN, AND ROLE OF A HERMIT CRAB POPULATION IN A SUBLITTORAL EPIFAUNAL COMMUNITY

The movements and activity of hermit crabs in a sublittoral soft-bottom community in the North Adriatic Sea (Gulf of Trieste) were monitored by means of observations by a SCUBA diver and time-lapse photography. Tagging experiments showed that the hermit crabs exhibit a pattern of movement which causes them to remain in a defined area for extended periods. During a two-year period, the radius of activity of a crab is estimated to be under 15 m. This leads to a high recovery rate of tagged shells. The average speed of a hermit crab was 2.1 m/h and the average distance travelled per day was 21.6 m as calculated from the analysis of the time-lapse films. This distance is an order of magnitude larger than that estimated from the tagging experiments (1.1 m/day). The activity of the crabs was restricted to the sediment surface between multi-species clumps. The approximate area of the sediment surface traversed by a crab is 0.4 m2/day. Many inter- and intraspecific encounters were observed, particularly among hermit crabs and the brittle stars Ophiothrix quinquemaculata (D.Ch.) and Ophiura lacertosa (Pennant). The daily activity pattern of the crabs is related to the light and dark phases on the sediment surface. The high density and conspicuous activity of the hermit crabs point to the important rôle of the pagurids in the investigated community. © 1979.