Use of macrobenthic infaunal communities in the monitoring and control of the impact of marine cage fish farming

Benthic macrofaunal community changes are used extensively to monitor the impact of polluting discharges to the marine environment. Regulatory and pollution control authorities have recognized the particular value of the well studied and reported responses of infaunal communities to organic pollution including wastes from aquaculture. Benthic systems are embraced in both the consent (licence) to discharge and monitoring procedures for marine cage fish farms in the Clyde River Purification Board's (CRPB) area. The relevant protocols of the CRPB are described and data are presented from impact studies throughout west central Scotland, focussing on the sedimentary environment (macrobenthos, organic carbon and redox: Eh). Macrobenthic infaunal responses, though not fully understood, were considered to provide the best measure to date of determining the impacts of organic wastes from cage fish farming and a possible way forward in developing benthic Environmental Quality Standards (EQSs) for aquaculture. Some patterns in physico-chemical data were identified, but frequently, the relationship both with benthic infaunal data and each other were inconsistent. Grossly impacted faunal communities varied little between sites and could readily be described by the simple community determinands of abundance (A), species richness (S) and Shannon Weiner diversity index (H). Moderate to lightly impacted zones were less easily defined but detailed faunal studies have allowed the selection of some widely distributed marker species. However, site-specific observations emphasized the site individuality and difficulties of setting EQSs across the industry. Using the principles of enhanced species populations and by identifying marker species, measurable impacts were found to extend further than previously reported. In naturally enriched systems, like the Firth of Clyde and some sea lochs, difficulty in separating slight effects from background was experienced. Continued monitoring and impact assessment, as well as building a better biological data base, may help develop appropriate benthic EQSs relating to aquaculture.