PATTERNS OF RECOLONIZATION AND THE IMPORTANCE OF PIT-DIGGING BY THE CRAB CANCER-PAGURUS IN A SUBTIDAL SAND HABITAT

The nature and level of disturbance to a benthic community caused by the pit-digging activities of the crab Cancer pagurus were examined in a shallow sub-tidal sand habitat on the west coast of Scotland. From observations by acoustic tracking we estimate that each individual digs between 6 and 7 pits d-1, with a total of 20 pits dug in a 1000 m2 area each day. Recolonisation of simulated crab pits suggest that the community returned to its original state within 25 to 30 d. This was achieved initially by erosion from the surrounding sediments, followed by the random arrival of adult colonists from the available benthic pool. Feeding or other competitive interactions within disturbed patches were not altered sufficiently to be reflected as changes in the relative abundance of taxa. We estimate that 3.6 % of the habitat will be at some stage of recovery from disturbance by pit-digging at this time of year.