Benthic recovery following cessation of fish farming:a series of successes and catastrophes

Abstract

After the removal of fish cages at an intensive aquaculture site, the sedimentary environment was monitored over 23 mo for redox potential, total organic carbon and nitrogen, total phosphorus, algal pigments and macrofauna. Three sampling stations were established: one under the previous location of the cages (R-0), a second one (R-10) at 10 m distance from the edge of the cages and a control site (R-c) at > l km distance. At both stations near the farming site the sediment was initially found to be anoxic and overlain by a highly organic black layer. Most geochemical variables at Stn R-10 attained values close to those at Stn R-c within 11 mo. Large fluctuations In the values of most variables were observed at Stn K-0 over the 23 mo, indicating that the environment had not fully recovered before the end of the observations. Similar results were obtained from the macrofaunal analysis, which revealed that after 2 3 mo a high proportion of benthic fauna at Stn R-0 was still composed of opportunistic species; abundance biomass and species composition showed marked successive changes in the direction of succession. This regression was attributed to a secondary disturbance due to a benthic algal bloom, caused by the seasonal release of nutrients from the farm sediment. It is concluded that the recovery process of heavily enriched benthos in a dynamic coastal environment is subject to the influence of different factors, resulting in progress and regression, and therefore the succession model proposed by Pearson & Rosenberg (1978; Oceanogr Mar Biol Annu Rev 161229-31 1) may not be applicable in the early stages of succession. KEY WORDS: Fish farms. Aquaculture. Benthic recovery. Redox. Organic carbon. Nitrogen. Phosphorus. Pigments. Macrofaunal succession. Abundance-Biomass Comparison curves O Inter-Research 1999 Resale of full article not permitted

Organic carbon content of sediments as an indicator of stress in the marine benthos

“…Eastern Mediterranean Sea: 199 stations from multiple sampling efforts conducted along the upper continental shelf of Crete (Karakassis & Eleftheriou 1997), in Heraklion Harbor (Lampadariou et al 2000), and in the Aegean and eastern Ionian Seas (Karakassis et al 1999. Samples are from sites with water depths of 10 to 190 m and salinity > 38 PSU.…”

Benthic recovery during open sea fish farming abatement in Western Mediterranean, Spain

“…In Greece, (Karakassis et al, 1999), total benthic recovery had not been achieved after 23 months, while in British Columbia, Brooks et al (2003) reported complete biological remediation after 6 months. At a Scottish sea loch, Pereira et al (2004) found that sampled stations were highly to moderately disturbed after 15 months.…”

“…Such recovery seems to follow defined patterns (Pearson & Rosenberg, 1978;Diaz-Castañeda, Frontier & Arenas, 1993). Going against the classical paradigm of succession as a continuum, Sanz-Lázaro & Marin Page 14 Karakassis et al (1999) introduced a different perspective for the recovery process.…”

“…In previous studies of benthic recovery after fish farming cessation (Karakassis, Hatziyanni, Tsapakis & Plaiti, 1999;Brooks, Stierns, Mahnken & Blackburn, 2003;Pereira, Black, McLusky & Nickell, 2004) the recovery rates observed in the different experiments differed to a large extent. In Greece, (Karakassis et al, 1999), total benthic recovery had not been achieved after 23 months, while in British Columbia, Brooks et al (2003) reported complete biological remediation after 6 months.…”

The influence of intensive fish nutrition on the quality of cooling waters

“…This renders it possible for fish to attain fast individual body weight growth and good condition. Intensive fish farming carries the risk of water pollution from the decomposition of unconsumed feed as well as the products of fish metabolism (Lewkowicz and Lewkowicz 1976, Karakassis et al 1999, Pereira et al 2004.…”