THE IMPACT OF HABITAT DISTURBANCE BY SCALLOP DREDGING ON MARINE BENTHIC COMMUNITIES - WHAT CAN BE PREDICTED FROM THE RESULTS OF EXPERIMENTS

Field experiments were conducted on 2 subtidal sandflats to identify t he short-term impacts of commercial scallop dredging on macrobenthic c ommunities. The 2 sites (1400 m(2)) were situated 14 km apart, both at about 24 m depth, with similar exposure aspects and were characterise d by infaunal communities dominated by small and short-lived species. Prior to dredging, preliminary sampling failed to reveal significant d ifferences in the density of common macrofauna within each site, altho ugh community composition was distinctly different between sites. The experiment was initiated by using a commercial scallop dredge to dredg e half of each study site. Macrofauna samples were collected in both t he dredged and adjacent reference plot at each site immediately after dredging and again 3 mo later. The density of common macrofaunal popul ations at each site decreased as a result of dredging, with some popul ations still significantly different from the adjacent reference plot after 3 mo. Significant compositional differences in the assemblage st ructure between dredged and reference plots were also recorded at each site over the course of the experiment. The findings of this experime nt are considered a conservative assessment of bottom disturbance by f ishing because of the area of seabed used, the types of community pres ent and the intensity of disturbance used in the experiment. The findi ngs of this and similar short-term experiments are discussed in light of the need to predict and assess possible large-scale changes to bent hic communities as a result of habitat disturbance by fishing.