Assessing trace-elements as indicators of marine finfish aquaculture across three distinct Canadian coastal regions.

Several trace-elements have been identified as indicators of finfish aquaculture organic enrichment. In this study, sediment sampling at finfish farms was completed as part of an Aquaculture Monitoring Program in three distinct Canadian regions. Despite diverse datasets, multivariate analyses show a consistent clustering of known direct (Cu and Zn) and indirect (Cd, Mo and U) tracers of aquaculture activities with sediment organic matter (OM) and/or total dissolved sulfides concentrations. OM content was also a predictor of Cu, Zn, Mo and U concentrations according to decision tree analyses. Distance from cages did not emerge as a strong driver of differences among sampling points; however, a tendency towards negative associations is clear especially for Zn. Enriched stations as determined after geochemical normalization were mostly localized within 150 m of net-pens. Selected trace-elements (in particular Zn) can be useful indicators of aquaculture organic enrichment in different ecosystems and valuable tools for monitoring programs.

Influence of salmonid aquaculture activities on a rock-cliff epifaunal community in Jervis Inlet, British Columbia.

Benthic video surveys were carried out at two marine finfish aquaculture and associated reference sites in Jervis Inlet (JI), British Columbia. Substrate composition, epifaunal diversity, mat-forming taxa (primary indicators: opportunistic polychaete complexes (OPCs) and sulfide-oxidizing bacteria) and waste pellets were quantitatively assessed. Hard-bottom substrates were dominated by rock wall, skeletal sponge matrix, graded bedrock, rock-veneer, and cobble. Aquaculture waste outputs (modelled depositional carbon fluxes and observations of waste feed/faecal pellets) were correlated with benthic organic enrichment indicators (OPC and sulfide-oxidizing bacteria). Sulfide-oxidizing bacteria varied in abundance up to a modelled depositional carbon flux of ~2gCm-2day-1 where it sustained 50% areal coverage. Glass sponges revealed an inverse relationship with aquaculture waste outputs and sulfide-oxidizing bacteria. Plumose anemones and shrimp showed a low frequency of occurrence at reference sites; however, they were abundant within the near-field zone of the aquaculture sites associated with a higher modelled carbon flux. Future research should focus on the response of various taxa to depositional gradients and their potential role as secondary indicators of aquaculture activities associated with rock-cliff communities.

Distinguishing between natural and aquaculture-derived sediment concentrations of heavy metals in the Broughton Archipelago, British Columbia.

Marine sediment samples were collected in the Broughton Archipelago, British Columbia, to assess the use of a geochemical normalization technique in the identification of a chemical tracer of aquaculture waste material. Zinc and copper were suggested as tracers of feed pellets, while copper was considered an indicator of anti-foulant agents used on netpen systems. The sediment samples were analyzed for carbon, nitrogen, organic matter, water, trace-element, and free sulfide concentrations, and sediment grain-size distribution. Sediment texture analysis revealed a wide range of substrate types from sand to silty loam categories. Strong relationships between sediment texture, sediment porosity, and organic content were observed across both near-field and far-field stations. Excess zinc and copper sediment concentrations, identified using a lithium-normalization technique, were restricted to near-field sampling stations (0 and 30m from netpen systems). The relationships between these metal tracers and organic content and sulfur concentrations were explored to account for variations in sediment concentrations of zinc and copper.

The use of meiofauna as an indicator of benthic organic enrichment associated with salmonid aquaculture.

Sediment chemistry and meiofaunal samples were collected in the Broughton Archipelago, British Columbia, to examine the relationship between sediment variables and meiofauna diversity across near- and far-field gradients surrounding several finfish aquaculture operations. The sediment variables examined consisted of free sulfide concentrations, redox potential (E(NHE)), organic content, and sediment grain size. A strong trend between sediment texture and organic content was observed across all sampling locations, which reflected a wide range of sediment types (sand-silt) that exist within the Broughton Archipelago. The abundance of certain meiofaunal groups (kinorhynchs, crustaceans, polychaetes) declined in an asymptotic fashion with increasing free sulfide concentrations, an indicator of benthic organic enrichment. Within these relationships, low meiofaunal abundances occurred in fine sediments associated with higher organic contents. Although other groups (nematodes, foraminifera) showed a slight decline in abundance with increasing organic enrichment, a high amount of variability in abundance was observed at high free sulfide concentrations, rendering these groups not suitable as indicators of organic enrichment. This study reports both horizontal and vertical trends in meiofaunal distributions relative to free sulfide concentrations. The abundance of nematode and crustacean taxa decreased with sediment depth as well as increasing sulfide concentration, while polycheate abundance increased with increasing free sulfide concentration. The ratio of nematodes to copepods was also shown to represent the degree of organic loading associated with aquaculture operations and its application as an indicator of benthic impact is discussed.