Benthic organic enrichment from suspended mussel (Mytilus edulis) culture in Prince Edward Island, Canada

The effects of increased biodeposition within mussel (Mytilus edulis) farms on the benthic environment were investigated using surface sediment samples collected from 11 coastal embayments in Prince Edward Island (PEI), Canada. The degree of organic enrichment, determined using geochemical indicators (total free sulfides (S), redox potentials (EhNHE), water content (WC) and organic matter (OM)), was significantly greater in mussel leases compared to reference sites located both outside lease boundaries and in inlets not used to culture mussel (MANOVA, p < 0.001). Post-hoc tests showed that mean WC and OM, EhNHE potentials and S concentration were all significantly different between lease and reference sites (p ≤ 0.009). Temporal changes in organic enrichment conditions were detected by comparing our 2001 data to those previously reported from a 1997 survey of the same sampling sites (MANOVA, p < 0.001). This multivariate effect resulted primarily from a 39% increase in mean S concentration between 1997 and 2001 (p = 0.029). Surface sediment variables at reference sites were similar between years. Benthic conditions were discriminated along an oxic–anoxic enrichment gradient using multidimensional scaling analysis. Mussel lease sites sampled in 1997 were clustered within predefined oxic sediment classifications along with the majority of reference sites, but were grouped farther along the enrichment gradient in 2001. The significant increase in hypoxic and sulfidic sediments within mussel farms between 1997 and 2001 is consistent with the 43% increase in PEI mussel production—a classic response to excessive organic biodeposition in shallow coastal inlets with relatively low dispersive capacity.