Faunal associations on scallop grounds in the western Gulf of Maine

Abstract

Benthic photographic transects were made during 1986–1987 across productive scallop beds on Jeffreys and Fippennies Ledges, western Gulf of Maine, from a manned submersible at depths of 56–84 m. Three megafaunal invertebrates dominated at each site: the sabellid worm Myxicola infundibulum (Renier) (mean densities ranging from 3.3 ± 4.2 to 7.1 ± 9.6· m −2); the burrowing cerianthid anemone Cerianthus borealis Verrill (1.0 ± 1.2 to 2.0 ± 0.5· m −2); and the sea scallop Placopecten magellanicus (Gmelin) (0.2 ± 0.5 to 1.0 ± 2.2· m −2). All three species exhibited contagious distributions (i.e., occurred in largescale clusters or patches), which could be modeled by negative binomial functions. On Fippennies Ledge, where little scallop dredging occurred in 1986, but, where appreciable fishing was conducted in 1987, sea scallops were positively associated with M. infundibulum and negatively associated with C. borealis in both years. In contrast, the association between M. infundibulum and C. borealis changed from a significant negative association in 1986 to random in 1987. The marked increase in scallop dredging on Fippennies Ledge between 1986 and 1987 was apparently the cause of a significant decline in the mean densities of all three megafaunal species (70% decline in sea scallops; 25–27% decline in cerianthids and myxicolids), although the pattern of faunal association with the sea scallops remained intact. On Jeffreys Ledge, where intensive dredging had occurred prior to our 1986 sampling, the pattern of faunal association described for Fippennies Ledge was absent. Thus, natural faunal associations may be severely impacted by fishing operations. We propose that C. borealis controls the spatial distribution and patch size of both M. infundibulum and P. magellanicus by preying on the larvae of the latter two species.