Does aquaculture impact benthic algal ecology? a study on the effect of an experimental cage aquaculture operation on epilithic biofilms

Abstract

Epilithic biofilms were monitored for potential impacts of an experimental rainbow trout aquaculture operation at the Experimental Lakes Area in northwestern Ontario, Canada. Metabolic and particulate samples were collected from the middle littoral zone of the experimental and reference lakes before and during the aquaculture operation. Phosphorus stocks in the experimental lake (epilimnetic and epilithic) increased as a result of both food waste and fish excretion. These cumulative P inputs were predicted to increase epilithic biomass and productivity, cause major compositional changes in the dominant groups and increase epilithic algal toxin production (microcystins). However, no major aquaculture-related changes in algal biomass, productivity, toxins or group dominance were observed in the epilithon. The only observed changes occurred at the species-level. These species-level changes were transient but did allude to an ecosystem reacting to stress.