engleski

Impacts of long-term fish farming effects on diversity and spatio-temporal variability of meio- and nematode assemblages in Limski kanal bay (Northern Adriatic Sea)

Fish farming generates organic waste consisting of unconsumed food, fecal and excretory matter and represents a point source of pollution that can seriously affect local marine environment. The impacts of cage culture on sediment are much greater than the effects on water quality. One of the main threats is organic overloading of sediments and consequential impacts on the benthic biota. In the sheltered and relatively shallow coastal areas in which most farms are located, the particulate waste matter accumulates under and near the cages which can result in oxygen depletion, bottom anoxia and the production of toxic gases adversely affecting benthic organisms. The scale of environmental impact would depends on the intensity of fish culture operations, stocking density and feed input, but also on the hydrographic conditions of the farm site. This study aimed to assess the long-term fish farming effects on meiofauna and nematode assemblage’s structure in Limski kanal bay. It is sheltered and semi-enclosed bay with low water exchange and silty bottom and therefore typical area of high environmental risk. Meiofauna and nematode assemblages structure were studied at five sites under the fish farms and two control sites located at 20 meters and 1 km seaward from the fish farm area. Sampling was performed in two contrastive periods (summer vs. winter season) related feeding rate and biodeposition. At all sites meiofauna assemblages was dominated by Nematoda (69-92%), followed by Copepoda (2-20%) and Polychaeta (1-10%). During the investigation, 64 free-living Nematoda species, comprised of 50 genera and 25 families were recorded. Statistical analyses pointed out significant differences in meio- and nematode assemblage’s structure between the sites underlying the fish farms and 1 km away reference site that differed in taxonomic composition and richness, as well as in diversity of nematode species. The results suggested a localized environmental impact that is restricted to the farming area.

meiofauna; nemtodes; fish farming; biodiversity

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