Macrobenthic density, biomass, and fauna of intertidal and subtidal sand in a Magdalen Islands lagoon, Gulf of St. Lawrence

Abstract

A survey of intertidal and subtidal macrofauna (>0.5 mm) was made of a sandy bottom lagoon on the Magdalen Islands, Gulf of St. Lawrence, in June 1975. Intertidal densities averaged 11 223.8 individuals∙m−2 and biomass 8.8 g∙m−2 while subtidal densities averaged 3398.1 individuals∙m−2 and the biomass 6.4 g∙m−2. Bivalves, polychaetes, gastropods, and crustacea constituted the bulk of the fauna. In the intertidal zone, the biomass was dominated by the bivalves, but in the subtidal region the polychaetes were the dominant group. Numbers and weights were highest in the lower half of the intertidal zone and lowest in its upper half and in deeper water. Compared with other intertidal and subtidal communities from the eastern coast of North America, species richness, density, and biomass in the study area were low. Estimates of productivity were roughly comparable with those reported from the coasts of Britain, Florida, Aldabra Atoll, and the northwest Mediterranean, but they were probably much smaller than those expected from the biomass measurements reported for the New England coast and from Prince Edward Island in the Gulf of St. Lawrence.