Experimental collection of great scallop postlarvae and other benthic species in the Bay of Brest: settlement patterns in relation to spatio-temporal variability of environmental factors

Abstract

Settlement patterns of great scallop (Pecten maximus) postlarvae and other benthic species in the Bay of Brest were studied from 2-D and 3-D collectors to clarify biotic interactions at the postlarval stage. Plane tiles became colonized mainly by epifaunal suspension feeders, while the 3-D substrata collected a more diverse fauna. Both species diversity and total abundance were higher in Netlon bags, compared with sandstone tiles. However, hydroids, bryozoans, tubicolous polychaetes, a number of epifaunal molluscs and macroalgae were more abundant on tiles. Between-sites differences in taxonomic group abundances mostly reflected the benthic fauna and flora beneath the collectors and would be explained by differential settlement and survival, according to local environmental conditions. Sediment type, depth, salinity, water turbulence, food and biotic interactions would be the factors regulating settlement. Bryozoans, hydrozoans, Anomia ephippium, Crepidula fornicata, mussels, tubicolous polychaetes, Pisidia longicornis, Hiatella arctica, Aequipecten opercularis and Chlamys varia were the main potential competitors of Pecten maximus collected. Crabs and Nassaridae would account for most of the potential scallop predators. Possible ways of improving scallop spat collection and cultivation are discussed with reference to the efficiency and placement of collectors, to environmental characteristics and to the intensity of biotic interactions at the postlarval stage.