The utility of artificial collectors as a technique to study benthic settlement and early juvenile growth of the rock crab, Cancer irroratus

Abstract

Concurrent studies of planktonic larval density and benthic recruitment of Cancer irroratus were performed in Kochibouguac Bay, New Brunswick, from late May to mid-September 1981. Three artificial collector types were used; mop, box and Witham. All collector types were shown to sample settling C. irroratus. Although Homarus americanus is also abundant in this region, no settling stages or young juveniles were observed in the collectors. The most efficient collector appears to be the mop type, which should be tethered off the bottom to avoid excessive clogging on mud bottoms. The usefulness of these collectors in the study of growth of these otherwise inaccessible stages was demonstrated using modal analysis of size-frequency histograms. In addition, the presence of 26 exuviae (2.5–58 mm carapace width) showed that juveniles of all sizes molt in these collectors. The larval density data revealed a clear sequence of events, comprising the appearance of the first zoea larvae in early summer, the presence of a large megalopa peak in mid-July, followed immediately by the appearance of new recruits (⩾ first crab stage) in the collectors. The use of such artificial collectors constitutes a promising technique in the study of benthic recruitment and early growth of C. irroratus.