Influence of mussel aquaculture on sediment organic enrichment in a nutrient-rich coastal embayment

Abstract

Effects of mussel Mytilus edulis aquaculture on benthic organic enrichment were determined in Tracadie Bay, a shallow, nutrient-rich embayment in Prince Edward Island, Canada. Water content (WC), inorganic grain size (GS), organic matter (OM), redox potentials (Eh NHE ) and free sulfides (S) in the upper 2 cm of sediment were measured at 58 stations throughout the inlet to evaluate spatial variations between lease and non-lease locations. MANOVA results showed that mean (± SD) values for WC (64.8 ± 12.7%), OM (9.8 ± 4.3%), and S (1794 ± 771 µM) were significantly (p < 0.005) higher and Eh NHE lower (-51 ± 78 mV) within mussel leases (n = 24) vs. non-lease areas (n = 34). Negative regressions between S and GS and positive regressions between Eh NHE and GS at lease and non-lease locations had similar slopes but intercept values were significantly higher for S and lower for Eh NHE (p < 0.007) for lease locations. Eh NHE and a Benthic Enrichment Index derived from Eh NHE , OM and WC were inversely related to S. K-means clustering and multi-dimensional scaling showed that geochemical variables could be used to group stations into categories of benthic organic enrichment within mussel lease and non-lease areas characteristic of oxic-hypoxic sediments described by measures of S and Eh NHE .

Magnitude, spatial scale and optimization of ecosystem services from a nutrient extraction mussel farm in the eutrophic Skive Fjord, Denmark

“…An additional constraint for optimizing an extractive mussel farm is the possible effects on benthic habitat and communities from the deposition of organic matter in mussel faeces and pseudofaeces. Observations of benthic effects from bivalve farming are generally limited to the immediate vicinity of the farm in shallow, poorly flushed regions (Chamberlain et al 2001, Hartstein & Stevens 2005, Hargrave et al 2008, Carlsson et al 2009, Cranford et al 2009. Benthic impacts at the Skive Fjord mussel farm were shown to be limited compared to the surrounding area due to the high rate of sediment organic enrichment from eutrophication (Holmer et al 2015).…”

Macrofaunal Spatial Patterns in Relationship to Environmental Variables in the Richibucto Estuary, New Brunswick, Canada

“…Hargrave et al (2008) examined sediment quality as well as sulfides and redox potential in Tracadie Bay, an estuary of the southern Gulf of St. Lawrence in adjacent Prince Edward Island. They determined that sulfide and redox were more sensitive indicators of mussel culture impact, and that aquaculture impacts were detectable using these variables.…”

“…The imposition of aquaculture onto estuaries has the potential to affect the forcing of benthic communities largely through organic loading and subsequent oxygen stress. Aquaculture is often at fixed locations and the local effects of the benthos are well documented with respect to sediment quality and benthic community health (Castel et al 1989;Crawford et al 2003;Mallet et al 2006;Hargrave et al 2008). Far field effects of aquaculture are difficult to detect and quantify, but multiple farm sites in a given region have the capacity to cause ecosystem level impacts.…”

Open water integrated multi-trophic aquaculture: constraints on the effectiveness of mussels as an organic extractive component

“…Burkholder & Shumway 2011, McKindsey et al 2011. Larger-scale adverse impacts have been observed under site-specific conditions of relatively poor water flushing, high culture density, shallow water, and/or the presence of additional sources of organic enrichment (Hargrave et al 2008a, Cranford et al 2009). Given that the mussel component of an open water IMTA system requires high culture densities in an extensive arrangement to be partially effective at capturing all of the suspended wastes (see above), the possible cumulative effects of organic biodeposition from both the fed fish and the organic extractive IMTA components need to be carefully considered.…”