Response to organic enrichment of infaunal macrobenthic communities under salmonid seacages

The response of infaunal macrobenthic communities beneath salmonid seacages to solid organic wastes (food pellets and fish excreta) was tested by means of the ABC-method (abundance, biomass comparison method: Warwick 1986) on samples collected from the SAFCOL seafarm at Badger Cove, southeast Tasmania, from February to July 1988. The intermittent nature of the addition of organic waste allowed us to monitor decline and recovery of the macrofauna, i.e., harvesting of a cage permitted a period of recovery whilst restocking precipitated a decline. The ABC-method proved to be a sensitive indicator of community health. Under a normal feeding regime the macrofaunal community structure indicated a moderately disturbed condition. Only 7 wk after the cage was harvested, species richness had increased markedly and the community adopted an undisturbed condition. Further improvement was apparent 14 wk post-harvest. Similarly, a decline to a moderately disturbed condition was apparent 7 wk after restocking and species richness had declined. No such changes occurred under a cage which contained fish continuously over the same period.