Recovery of sediments after cessation of marine fish farm production

Following cessation of fish production at a fish farm site in Loch Cretan, Scotland, a study of the recovery of the benthic environment was undertaken. Sediment samples for macrofauna and geochemical parameters (redox potential, organic carbon, oxygen flux) were collected over a period of 15 months from three stations following a gradient of impact from the former fish farm site. The data collected were analysed by a combination of uni-and multivariate statistical methods. The macrobenthic community at the two stations furthest from the fish cage site showed signs of recovery with time in terms of indicator species, number of species and abundance, being, however, still moderately to slightly disturbed at the end of this study. At the station nearest to the former fish cage site, recovery of the macrobenthic community was also evident, but this station was still highly impacted 15 months after fish production ceased, with opportunistic species dominant. Fifteen months after fallowing, highly reduced conditions were still persistent in subsurface sediments at the stations on the periphery of the former fish cage site. Bulk sediment organic carbon, although an indicator of a spatial gradient, was not found to be a significant indicator of recovery. Combinations of different environmental parameters appear to affect different stages of benthic recovery with sediment oxygen uptake as the main observed parameter conditioning early stages of macrobenthic succession. (C) 2004 Elsevier B.V. All rights reserved.