On the impact of a sea bass (Dicentrarchus labrax L.) cage farm on water quality and macrobenthic communities

Abstract

      In Croatia, the marine fish farming industry has developed over the two decades. Therefore, the floating cages are now located in the majority of semi-enclosed coastal basins. The expected expansion of industry, in terms of new locations and increased production of existing ones asks for the proper assessment of potential impact of the farm in its surrounding environment.

      This paper presents the first study on water quality and benthic community in an inshore sea bass cage farm producing around 200 t y ^-1 over almost 15 years. The relationship between feed supply and the effect parameters like nutrient content, phytoplankton biomass, and organic matter in sediments was found rather weak. However, significant changes in the oxygen saturation in the cages during the sum­mer were recorded, when it occasionally may drop bellow 70% in the morning time. Survey on mac­robenthic communities showed benthic flora and fauna still quite rich and diverse. On the other hand, with respect to its composition, structure, and distribution, some benthic components were clearly affected by the fish farm. Well-developed Posidonia oceanica beds have almost disappeared beneath the cages and they are in regression in the entire bay. In the water of farm surroundings, some nitrophilic algal species dominated the biomass, while the number of Chlorophyta exceed the one of Phaeophyta.

      Based on these results, it appears that further enrichment of the bay should include such a moni­toring effort, which will ensure that observed ecological changes associated with the farming activities are kept within acceptable levels.