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Effects of nutrient release from Mediterranean fish farms on benthic vegetation in coastal ecosystems

Fish farming is a rapidly growing industry worldwide, particularly in the Mediterranean, where it is a relatively new. Mediterranean fish farms are often located in areas close to the shore, which, owing to their strong currents and coarse sediments, are suitable habitats for dense seagrass meadows. This can lead to conflicts of interest between efforts to protect and conserve seagrass in coastal zones and fish farming activities.

The main objectives are to study the environmental impact of fish farming on benthic vegetation (seagrass and macroalgae) and benthic fauna, as well as to provide new insights for monitoring purposes.
The specific objectives are to explore:
1) the loss of nutrients from Mediterranean fish farms
2) the incorporation of nutrients into pelagic and benthic vegetation surrounding fish farms
3) the impact of released nutrients and fish farm effluents on benthic vegetation and fauna, and the evaluation on whether seagrass and benthic fauna can be used as early warning indicators of the impact of fish farming
4) the information obtained on nutrient releases and the effects of these nutrients on pelagic and benthic vegetation will be incorporated into a dose/response model. It is important to promote the exchange of knowledge between scientists and end users through workshops and conferences.
The project focuses on nutrients released from the farms and will provide a dose/response nutrient model that can be used by fish farming professionals to improve production strategies and by policy-makers at national and EU level.

Progress to Date
Fish farms have been selected to represent the different environmental conditions in the Mediterranean (from oligotrophy to ultra-oligotrophy). All farms have seagrass or macroalgae present under the net cages or in close proximity to them. The project has been concentrating on intensive field campaigns, where all partners work together at the fish farms, supplemented with follow-up activities and experimental studies carried out by each partner.
The hydrological regime of the site was investigated, and water samples were taken to examine nutrient dynamics. Incubations with phytoplankton and macroalgae were deployed to assess nutrient availability in the fish farm surroundings. Seafloor (sediment) samples were taken along a transect away from the farm to examine the organic matter composition, microbial communities and activities, decomposition and nutrient regeneration. Samples were also taken for analysis of bottom fauna. The seagrass communities were studied in detail and permanent measuring units were installed in a transect from the farm.

Sampling of the water column at the two examined fish farms shows that fish farming has little impact on the nutrient concentrations and water quality.
The sediment analysis show that the organic loading is probably enhanced at both sites, although this was only verified in Sicily, and there was a clear effect of organic loading on the sediment oxygen uptake and nutrient dynamics at both sites.
The seagrass (Posidonia Oceanica) meadows situated near the studied fish farms are clearly affected by farming activity. Organic loading of the sediments appears to be a good indicator of fish farm impact on seagrass. The distance from the farms is also a good descriptor and relates to impact on seagrass cover and biomass, which decrease close to the farms. In contrast, herbivore pressure, epiphyte and macroalgae cover increase closer to the net cages. Physiological parameters, such as rates of photosynthesis and respiration, however, show no significant effects on farming activities.


Scientist responsible for the project

Campusvej 55
5230 Odense M
Denmark - DK

Phone: +45 65 502605
Fax: +45 65 930457


Project ID QLRT-2000-02456
Organisation University of Southern Denmark
Area 5.1.2
Start date 01 December 2001
Duration (months) 36
Total cost 2 451 348 €
Total EC contribution   1 693 711 €
Status Completed
Web address of the project

The partners

  • National Environmental Research Institute, Denmark - DK

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