Movements of Individual Members in a Population of the Shore Crab, Carcinus maenas L., in the Littoral Zone

Abstract

The method of marking, release and recapture was applied simultaneously for a period of two weeks to populations of crabs inhabiting 3 rocky areas on a sandy shore. Samples of crabs taken from all 3 areas were measured. The "survival rates" for males indicated a daily immigration of 36 and 55, respectively, into the 2 on-shore areas, and of 74 into the off-shore area. These crabs could only have come from the sublittoral zone. Recaptures of marked males showed that there was much more interchange between the 2 on-shore areas than between either of these and the off-shore one. Males taken from the off-shore area were consistently larger than those taken from either of the onshore areas, but those from the on-shore areas did not differ significantly from each other. It is concluded that there is a rapid up and down migration, in which the majority of the crabs take part, others remaining mainly at the same level. There was no significant difference between the mean sizes of the females in the 3 areas. Changes in numbers suggest that there were gradual movements of the whole population between the littoral and sublittoral zones. These may have been part of a rhythmic behavior pattern or have been caused by some environmental factor such as rough seas.