Increased plastic ingestion by fish in the South Pacific oceanic accumulation zone

International audienc

A pearl of a partnership

Pearl farming is essential to the economy of French Polynesia, generating thousands of jobs for the islands. What are the main concerns for the current state of pearl farming in the region

Different food particle sources in the pearl oyster Pinctada margaritifera and its epibionts

Suspended bivalve culture (e.g. longlines) transfers benthic biomass - including bivalves and various epibionts - toward the water column, creating strong trophic interactions with the planktonic compartment. Trophic interactions are of central interest for ecologists, yet not well understood in coastal lagoon food webs, especially in tropical areas. Using stable isotope (SI) analyses, this study explored the trophic relationships between marine particulate organic matter (POM), pearl oysters and epibionts, in two contrasted production areas in French Polynesia. Different size classes of POM (0.7–2 µm, 2–20 µm, 20–80 µm, 80–250 µm and >250 µm) were well discriminated both by their δ13C and δ15N signature and results showed a low dietary overlap between pearl oysters and epibionts, likely due to assimilation of large particles in greater proportion by pearl oysters. Pearl oyster diet may vary in time in relation with variations of the basal trophic resource and selective feeding, such that their isotopic signature is more variable compared with that of epibionts. Pearl oysters and epibionts might alter nutrient cycling in a different way as reflected by their different tissue C:N

The plate collector, a new option for Pinctada margaritifera spat collection in French Polynesia

International audienceThe aquaculture industry can constitute an important source of waste in the environment. In atoll lagoons of French Polynesia, among the materials used by pearl farmers, shade-mesh collectors can release toxic substances and are responsible of microplastics production. With the aim of providing a less polluting alternative, we performed in situ tests comparing reusable plate collectors and shade-mesh collectors during 16 months. Plate collectors were significantly more efficient for spat collection, especially after the first 6 months of immersion (P < 0.0001). These results confirmed that this device can be a suitable and more sustainable alternative for the pearl industry

Different food particle sources in the pearl oyster Pinctada margaritifera and its epibionts

WOS:000706788500001International audienceSuspended bivalve culture (e.g. longlines) transfers benthic biomass including bivalves and various epibionts toward the water column, creating strong trophic interactions with the planktonic compartment. Trophic interactions are of central interest for ecologists, yet not well understood in coastal lagoon food webs, especially in tropical areas. Using stable isotope (SI) analyses, this study explored the trophic relationships between marine particulate organic matter (POM), pearl oysters and epibionts, in two contrasted production areas in French Polynesia. Different size classes of POM (0.7-2 mu m, 2-20 mu m, 20-80 mu m, 80-250 mu m and \textgreater250 mu m) were well discriminated both by their delta C-13 and delta N-15 signature and results showed a low dietary overlap between pearl oysters and epibionts, likely due to assimilation of large particles in greater proportion by pearl oysters. Pearl oyster diet may vary in time in relation with variations of the basal trophic resource and selective feeding, such that their isotopic signature is more variable compared with that of epibionts. Pearl oysters and epibionts might alter nutrient cycling in a different way as reflected by their different tissue C:N

Preface: Research and Management for the Conservation of Coastal Lagoon Ecosystems, South–North Comparisons

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Biogeochemical flux associated to pearl farming activity and ecological consequences on water-column

International audienc

Conservation and resource management in small tropical islands : trade-offs between planning unit size, data redundancy and data loss

Resource management and conservation require the definition of planning units (PUs), i.e., the spatial domain where management decisions are applied. PUs are either pre-established in size and shape following management constraints or are data driven(DDPUs) by overlay of multidisciplinary data layers. The trade-offs between these two approaches have not been investigated previously for small tropical islands and their characteristics. Here, we use resource density, fishing pressure and susceptibility to mortality for a giant clam fishery in a small French Polynesia atoll to discuss the suitability and impact of the two approaches in conservation management. Aggregation to pre-established PU grids highly affected data even for PU as small as 2500 m(2), with higher loss of spatial information for density and fishing effort. By contrast, DDPU rendered well small scale patterns of interest but reduced redundancy. Our results stress the importance of considering the initial patterns of data in the definition of planning units, and we suggest a 3 steps process to identify adequate trade-offs between PU size, PU redundancy and data loss to properly draw practical recommendations for small islands

Trophic relationships between the farmed pearl oyster Pinctada margaritifera and its epibionts revealed by stable isotopes and feeding experiments

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 margaritiferaand its epibionts, using stable isotope analysis and feeding experiments. Inter- and intraspecificvariations of δ13C and δ15N 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 naturalconditions. 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 δ13C signature of ascidians (−21‰) was lower than that of oysters (−18‰), indicating a difference in organic matter sources ingested by thesefilter 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 ambientwater (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