This study investigated the role of wild fishes associated with marine farms as potential consumers of organic waste in the water column and sediment. Experiments were carried out at a fish farm in a semi-enclosed bay in the Mediterranean Sea (SE Spain). Sediment traps collected organic waste from net-pens in the water column at different depths during June and July 2001 and benthic caging experiments were carried out on the sediment from October 2000 to January 2001. The experiment showed that about 80% of the particulate organic matter leaving the rearing net-pens may be consumed before it settles on the sediment. Significant changes in the nutrient quality of the organic matter exported are also due to consumption by wild fishes. Wild fishes thus play an important role in recycling the organic matter of the sediment, and regulate the benthic community structure. Our results indicate that the trophic role of wild fishes should be considered when evaluating the environmental impact of fish farms.
SUMMARY:The sediment formed by the tailings of an abandoned mine, which discharged into Portmán Bay, Murcia, SESpain, was tested to establish a possible gradient of heavy metals. The results were compared with tolerance limits of what was calculated from control sites. Whole sediment toxicity tests were performed on two amphipod species, Gammarus aequicauda and Microdeutopus gryllotalpa, while sediment-water interface and porewater toxicity tests were performed on three sea urchins species, Arbacia lixula, Paracentrotus lividus and Sphaerechinus granularis. The sensitivity of these marine organisms was evaluated by exposure tests using the reference substances: ammonium chloride (NH 4 Cl), cadmium chloride (CdCl 2 ), potassium dichromate (K 2 Cr 2 O 7 ), sodium dodecyl sulfate (C 12 H 25 NaO 4 S) and zinc sulfate (ZnSO 4 ). The concentration of heavy metals decreased along the pollution gradient. Amphipod 10 day acute toxicity tests clearly demonstrated the gradient of toxicity. The sediment-water interface tests conducted with sea urchins also pointed to a pollution gradient and were more sensitive than the tests involving amphipods.Key words: amphipods, sea urchins, toxicity; sediment-water interface, pollution. RESUMEN: ENSAYOS CON ANFÍPODOS Y ERIZOS DE MAR PARA EVALUAR LA TOXICIDAD DE SEDIMENTOS MEDITERRÁNEOS: ELCASO DE LA BAHÍA DE PORTMÁN. -Los sedimentos formados por los estériles de una mina abandonada, que fueron descargados en la bahía de Portmán, Murcia, SE de España, fueron sometidos a ensayos para establecer un posible gradiente de metales pesados. Se realizaron ensayos de toxicidad total de los sedimentos en dos especies de anfípodos, Gammarus aequicauda y Microdeutopus gryllotalpa, mientras que se realizaron ensayos de toxicidad de la interfase sedimento-agua y del agua intersticial en tres especies de erizos de mar, Arbacia lixula, Paracentrotus lividus y Sphaerechinus granularis. La sensibilidad de estos organismos marinos se evaluó mediante ensayos de exposición que utilizaban las siguientes sustancias de referencia: cloruro amónico (NH 4 Cl), cloruro de cadmio (CdCl 2 ), dicromato potásico (K 2 Cr 2 O 7 ), dodecil sulfato de sodio (C 12 H 25 NaO 4 S) y sulfato de zinc (ZnSO 4 ). La concentración de metales pesados disminuyó a lo largo del gradiente de contaminación. Los ensayos de toxicidad aguda durante 10 días demostraron claramente el gradiente de toxicidad. Los ensayos de interfase sedimento-agua realizados con los erizos de mar también indicaron un gradiente de contaminación y fueron más sensitivos que los ensayos con anfípodos.Palabras clave: anfípodos, erizos de mar, toxicidad, interfase sedimento-agua, contaminación.
Tuna farming is based on fishing bluefin tuna in their natural habit of the western Mediterranean and fattening them in floating cages. Although this type of aquaculture is expanding rapidly in the Mediterranean Sea, very little information is available for an environmental impact assessment and environmental monitoring of tuna ranching. Spatial and temporal scales of impact need to be established before the norms and regulations affecting this new branch of aquaculture can be properly implemented. The biotic indices measured pointed to detectable impact only under the cages, although multivariate techniques defined an environmental gradient of stressed macrofaunal assemblages. The benthic surveys carried out indicated that high impact was restricted to a radius of roughly 5 m from the cages with a transitional radius at 35 m. This zone was characterized by high densities of opportunistic species. There was a further zone of moderately stressed benthic environment extending to about 180–220 m from the cages. This moderately stressed zone exhibited slight changes in community structure, because the densities of some species were stimulated. At distances greater than 220 m from the tuna farm, the system apparently returned to normal conditions. The fallow period produced partial remediation of the area affected, except in the sediment underneath the cages where even a 6‐month fallow period was not sufficient for the community to totally recover.
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