Bivalve aquaculture is worldwide impacted by biofouling development. Immersed infrastructures and shells of the reared species create new substrate for a wide range of epibionts, mainly composed of suspension feeders. Biofouling development is generally considered as a plague for bivalve aquaculture, and its control results in additional costs that can represent up to 30% of total operational costs of the industry. Epibionts have not only consequences for the species they overgrow (i.e. basibiont), but they can also alter the ecological functioning of the exploited ecosystem. In this review, we point out that the assessment of the net effect of biofouling is more complex than expected, as it combines negative and positive effects on both the commercial production and the ecosystem. Furthermore, we emphasize that the removal of biofouling can be stressful and damaging for the reared species. Biofouling control should be carefully reconsidered, on the basis of a holistic approach considering: (i) the interactions between epibionts and their basibionts; (ii) its impact on the final product; and (iii) its contribution to the sustainability of the ecosystem.

Ensuring sustainable management of the emerging open-ocean aquaculture industry requires an understanding of how this activity interacts with the surrounding environment. We examined the effects of an offshore mussel farm on sedimentation rates, sediment sulfide levels and macro-infaunal communities near Îles-de-la-Madeleine, eastern Canada. The farm had been in production for 6 yr and is located in a deep (19 m) high-energy environment. The impacts were examined for 2 densities of mussels (standard and double) and at different periods of the year. There was no sign of excessive organic enrichment or a clear pattern of a significantly modified benthic environment. However, some organisms likely benefited from the biodeposits and fall-off of mussels (and associated communities), and the farm presumably induced heterogeneity in the distribution of infaunal communities, likely due to variation in the dispersion of biodeposits caused by the structure of the longlines and local hydrodynamics. Annual and interannual variability appear stronger than the influence of the farm, and no detrimental effects are suspected. This study provides baseline information about the limited documented effects of open-ocean bivalve aquaculture on the benthic environment.

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Bivalve cultivation can significantly contribute to nutrient cycling in semi-enclosed ecosystems. We investigated the influence of suspended pearl oyster culture on nutrient regeneration in the water column of 3 oligotrophic lagoons in French Polynesia. The aim of this first study performed in a tropical area was to assess the seasonal variability of nutrient fluxes and to quantify the contribution of biofouling communities. In situ metabolic enclosure systems were used to measure nutrient uptake or release by 'cultivation units' (i.e. 4 pearl oysters with or without associated biofouling). In all 3 study lagoons (Tahiti, Mangareva, Ahe), nutrient fluxes produced by pearl oyster and associated biofouling communities (CR units) were 4-to 6-fold higher than those measured for cleaned pearl oysters. CR units can release dissolved inorganic nitrogen and soluble reactive phosphorus in the water column at a rate of 200 and 50 µmol h −1 , respectively. Trophic level and composition of biofouling communities may explain the variations of fluxes observed between the different islands. At the pearl farm scale (Ahe), pearl oyster long-lines may supply 70% of the inorganic nitrogen demand for primary production, with biofouling communities accounting for 60% of the total nutrient release. Pearl oyster culture enhances nutrient availability and alters stoichiometry, which can strongly modify the dynamics of the planktonic ecosystem.

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Bivalve cultures support a host of epibionts, mainly suspension feeders, which can compete for food resources with the cultivated bivalves. However, the magnitude of interspecific competition for food in bivalve aquaculture settings remains inconclusive, especially in tropical areas. We investigated the interactions for food between the farmed pearl oyster Pinctada margaritifera and its epibionts, using stable isotope analysis and feeding experiments. Inter-and intraspecific variations of δ 13 C and δ 15 N stable isotope ratios (SIRs) were determined for oysters in the presence or absence of epibionts. The diet of the most abundant epibionts, Herdmania momus and Didemnum sp., was specified using isotope measurements and flow cytometry during feeding experiments, to determine the main phytoplankton groups consumed by these ascidians in natural conditions. The absence of intraspecific variation in SIRs among oysters with or without epibionts suggested that the diet of P. margaritifera was not affected by the presence of epibionts, indicating a reduced diet overlap and no food limitation. The δ 13 C signature of ascidians (−21 ‰) was lower than that of oysters (−18 ‰), indicating a difference in organic matter sources ingested by these filter feeders despite receiving the same food mixture. While the main carbon source of oysters came from large particulate organic matter (POM) > 20 µm, our results showed that the diet of ascidians mainly came from smaller particles (POM < 20 µm) and reflects the composition of ambient water (mainly picophytoplankton < 2 µm), which confirmed their lack of food selectivity. In the studied conditions, food competition between oysters and epibionts, specifically ascidians, was not a limiting factor, in spite of a diet overlap for nanophytoplankton.