Distribution and Association of Larval Crabs (Decapoda: Brachyura) on the Scotian Shelf

Abstract

Thirty-five taxa of neustonic larval Brachyura were distinguished and identified to stage of development in 3055 samples from the Scotian Shelf taken from north of Cape Breton to Georges Bank. A maximum of 17 species of larvae was taken in a single tow, with a norm of about 4 per tow. The most abundant species, collected in all stages of development, were the indigenous Chionoecetes opilio, Hyas araneus and Hyas coarctatus, Cancer borealis and Cancer irroratus, and Carcinus maenas. Biomass was dominated by the Hyas and Cancer species. Distributions of the three Majidae species indicated that larvae drift southwest along the shelf, and that they are indigenously derived. Twenty-six expatriate species occurred as megalopas only, predominantly offshore. Reciprocal averaging and factor analysis showed that there was considerable separation of the indigenous and expatriate larval species, but did not reveal strong relationships to environmental variables or ecological gradients. Recurrent group analysis indicated that community structure was weak and variable, but confirmed the virtual separation into indigenous and expatriate associations. An examination of co-occurrences of indigenous and expatriate species by stage of development showed strong patterns. We suggest that concurrent analysis of larval lobster and larval crab distribution patterns on the Scotian Shelf could indicate recruitment origin of lobsters (Homarus americanus).