MA8 Ecotoxicology of Tropical Aquatic Environments
A105 & A106
8:00 AM - 12:00 PM, Monday
(75A) Benthic communities and organic enrichment from coastal aquaculture - lessons about ecological relevance.
Bright, D1, 2, Klaver, M2, 3, McGreer, E4, Dalby, J4, Takaema, B4, 1 UMA Engineering Ltd., Victoria, BC, Canada2 Royal Roads University, Victoria, BC, Canada3 Fisheries and Oceans Canada, Port Alberni, BC, Canada4 BC Water Land and Air Protection, Nanaimo, BC, Canada
ABSTRACT- Open-net pen aquaculture is a potential source of organic loading to the local seabed within coastal environments, depending on local physical oceanographic conditions. It has long been recognized that seabed eutrophication - be it from municipal waste discharges, pulp and paper effluents, wood waste deposition, or other sources - has the potential to alter the structure and function of especially benthic infaunal communities, and to alter the successional sequence. In light of this, several jurisdictions have elected to manage coastal aquaculture activities in depositional environments based on indications of either elevated concentrations of free sulfides in near-surface sediments, impoverishment of the infaunal community, or both. Using recently collected data on sediment chemistry and infaunal community structure from salmon aquaculture sites in British Columbia, we show the statistical/predictive relationships between sediment chemistry and biological responses. Waste from salmon aquaculture (primarily feces and unutilized food pellets) is highly labile once deposited on the seabed, which has the positive effect of making seabed eutrophication effects highly transient after the grow-out cycle ceases, as well as the negative effect of resulting in rapid increases in microbial sulfate reduction and pore water sulfide concentrations. Variability in the lability of different types of organic waste are seldom fully appreciated in the management of coastal discharges. We explore the larger ecological relevance of the observed profound but transient change in benthic community structure within limited areas of seabed. Ultimately, challenges with finding ecologically meaningful thresholds for managing organic waste deposition point to similar problems with ecological relevance when using benthic community assessments on a site-specific basis as part of sediment quality triad approaches, environmental effects monitoring, or for ecological risk assessments in general. There is an urgent need for (i) assessment and measurement endpoints based on the benthic community that have larger ecological relevance than richness, abundance or statistically significant differences between sites (e.g. shifts in productivity:biomass ratios; loss of food resources for juvenile fish in nursery areas), and (ii) cumulative, integrated assessments that focus on ecosystem functioning and energy flow.
Key words: eutrophication, benthic ecology, sulfide, aquaculture