The European Union-funded ECASA project (Ecosystem Approach for Sustainable Aquaculture) studied the impacts from aquaculture on ecosystems from northern Norway to Greece. The objectives of this investigation were to identify quantitative indicators of the effects of aquaculture on marine communities, and to assess their applicability over a range of ecosystems and aquaculture production systems. The study included 6 Mediterranean and 4 Atlantic sites, 7 of which produced finfish (seabream, seabass, tuna, salmon and cod), and 2 bivalve molluscs (oysters, mussels, and clams); one site produced both fish and bivalves. Cultivation methods included finfish cages, long-lines and trestles. Similar sampling methodologies were employed at the 10 study sites, obtaining sediment, hydrodynamic, and benthic faunal data. The horizontal impact from organic enrichment extended 50 m from the farms, with contradictory responses in several indicators (individual abundance, biomass) and a more consistent response of the Infaunal Trophic Index (ITI) and AZTI's Marine Biotic Index (AMBI). By means of Partial Redundancy Analysis, it was demonstrated that the environmental variables explained 53.2% of the variability in the macrofaunal variables (individual abundance, species richness, diversity, AMBI and ITI), whilst the explained variance was partialled out within three groups of variables: (i) 'hydrography' (depth, distance to farm, average current speed), which explained 11.5% of the variance; (ii) 'sediment' (Eh and percentages of silt and total organic matter), which explained 5.4%; and (iii) 'cages' (years of production and annual production), which explained 15.2%. The shared variance explained by interactions among these groups was 21.1%. These results, together with multiple regression analysis, provide an accurate assessment of the degree of impact from aquaculture. In conclusion, the use of several benthic indicators, in assessing farm impacts, together with the investigation of dynamics of the studied location, water depth, years of farm activity, and total annual production, must be included when interpreting the response of benthic communities to organic enrichment from aquaculture.

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Growth of the black-lip pearl oyster, Pinctada margaritifera var. cumingi, was studied for an annual cycle, from March 1997 to April 1998, in the lagoon of Takapoto atoll (Tuamotu archipelago, French Polynesia). Growth in shell and in tissue were measured every 15 days on three successive age groups of cultivated pearl oysters. At the same time, hydrobiological parameters (temperature, salinity, oxygen concentration, suspended particulate matter), known to have influence on bivalve growth, were followed each week during culture. No seasonal trend was observed in hydrobiological parameters, except for temperature which varied between 26°C and 31°C. The potential food for pearl oysters (particulate organic matter, POM, mg l −1) was slightly concentrated, but always available, so that, in this lagoon environment, no period seemed to be unfavourable to pearl oyster growth. Effectively, growth in shell was regular and shell did not exhibit any annual ring. Nevertheless, as it is often the case for bivalves, shell growth showed a progressive decrease with the age of pearl oyster and followed a classical Von Bertalanffy model: H=160.5 (1−e −0.038 (t−3.73)) with H the shell height (in mm) and t the age (in months). On the other side, growth in tissue did not follow the same pattern than for shell: P. margaritifera exhibited reduced growth rate in tissue during the warm season (November-April) so that a seasonal growth model was more appropriate: W tissue =6.9/(1+e (5.58-0.208 t−0.435 sin (2π/12 (t−1.427)) with W tissue , the dry tissue weight (in g) and t the age (in months). Several results concerning growth rates should be of interest for pearl farming. Firstly, the progressive decrease measured in shell growth rate implies, for pearl seeding operations, that the sooner the nucleus is implanted, the greater is the rate of nacreous deposition on this nucleus, and shorter is the time to obtain a marketable pearl for farmers. Secondly, exhaustive comparison, between growth rates obtained in our study and those obtained in other lagoons, tended to demonstrate that there is a small but significant variability in growth between lagoons of the Tuamotu archipelago. Further investigations need to be engaged in order to determine the most suitable sites for pearl farming in French Polynesia. Finally, comparison between growth of P. margaritifera var. cumingi and growth of other pearl oysters showed that P. maxima but also P. margaritifera var. erythraensis would also exhibit fast growth in Polynesian waters and then, would constitute potential candidates for further Polynesian diversification projects.

We used a carbon-based food web model to investigate the effects of oyster cultivation on the ecosystem of an intertidal mudflat. A previously published food web model of a mudflat in Marennes-Oléron Bay, France, was updated with revised parameters, and a realistic surface area and density of existing oyster cultures on the mudflat. We developed 2 hypothetical scenarios to estimate the impact of oyster cultivation on the food web structure of the ecosystem: one with no oysters, the other with a doubled area devoted to cultivated oysters in the bay. Oysters are direct trophic competitors of other filter feeders, and their presence modifies benthic-pelagic coupling by forcing a shift from pelagic consumers to benthic consumers. Increasing the surface area of cultivated oysters caused secondary production to increase, providing food for top predators (in particular juvenile nekton), reinforcing the nursery role of the mudflat in the ecosystem, and altering the species composition available to the top predators.

In situ clearance rate (CR) and biodeposition of the black pearl oyster, Pinctada margaritifera, were followed during several field experiments from 1996 to 1998 in the lagoon of Takapoto. Serial measurements of total particulate matter (TPM, mg l −1), particulate inorganic matter (PIM, mg l −1), and particulate organic matter (POM, mg l −1) were related to meteorological conditions, especially wind speed. As a general case, POM and PIM increased with wind speed. Nevertheless, PIM increased faster than POM so that the organic content (OC, %) of the TPM decreased progressively when wind speed increased. These TPM variations induced direct changes in feeding processes of P. margaritifera. CR (l h −1) averaged 22 l h −1 for a pearl oyster of 1 g dry tissue weight and varied with POM, PIM and dry tissue weight (W, g) according to the following equation: CR=26.96 PIM −0.42 POM 0.96 W 0.61. This clearance activity appeared to be the highest of those mentioned for bivalve species in their natural habitats. Pseudofaecal (PF, mg h −1) production started for very low PIM load (i.e., 0.17 mg l −1) and POM load (i.e., 0.28 mg l −1) in water and followed the equation: PF=32.6(POM−0.28)(PIM−0.17)W 0.77. In other bivalve species, PF are generally observed for higher PIM or POM levels. These PF were mainly constituted of mineral matter (more than 80% in weight). Faecal production (F, mg h −1) increased with seston load and reached progressively a plateau (i.e., maximal intestinal transit time) as shown by the equation describing the faecal biodeposition F=20 W 0.49 (1−e −0.66 TPM). The quantity and the composition of the faecal biodeposit were in a range commonly found in literature. This work confirms, by in situ experiments, previous results obtained in laboratory and especially that P. margaritifera has developed a trophic strategy which consists of processing large amounts of water to gain sufficient energy in poor waters. But this work also showed that meteorological conditions have indirect influences on feeding processes of pearl oyster by modifying significantly the concentration and the composition of seston.