Effects of hydraulic dredging on the benthic ecology and sediment chemistry on a cultivated bed of the Northern quahog, Mercenaria mercenaria

We examined the effects of hydraulic dredging on the benthic ecology and sediment biogeochemistry of a leased shellfish bed in Long Island Sound near Milford, Connecticut, where Northern quahog or hard clam, Mercenaria mercenaria (Linnaeus 1758), aquaculture is conducted. Six 1 ha plots were sampled at 1-2 week intervals from June through October of 2010. One-time hydraulic dredging to harvest hard clams was conducted on 3 dredged treatment plots in mid-June, while 3 control plots remained not dredged. Repeated measures analysis indicated no significant differences between dredged and not dredged plots for any of the ecological indices or sediment chemistry measurements. Numbers of newly settled hard clams were significantly higher on dredged plots. Cluster analysis indicated a strong seasonal influence on benthic community structure distinguishing between early and late season assemblages. Hydraulic shellfish harvesting as conducted on leased beds in Long Island Sound did not appear to significantly impact benthic assemblages or sediment biogeochemistry, while sediment grain size and sampling date had a greater influence on benthic community structure.