Physical Factors of Differentiation in Macrobenthic Communities Between Atoll Lagoons in the Central Tuamotu Archipelago (French Polynesia)

Nine atolls were characterized in order to understand how physical factors control the species composition, diversity, and abundance of macrobenthic (coral, mollusc, echinoderm, and algal) communities inside the lagoons. Only one region, the central part of Tuamotu Archipelago, French Polynesia, was considered, in order to minimise the variation due to regional factors between regions. The lagoons investigated showed a gradient of physical factors, providing various landscape configurations. The physical factors were surface area, abundance of pinnacles, degree of hydrodynamic aperture, and relative importance of passes in this degree of aperture. Macrobenthic communities were characterized by low diversity and strong dominance of a few mollusc or echinoderm species that generally occurred in lagoons without passes. Correlation analyses indicated that species richness increases with the surface area of the lagoon. Species richness of corals, echinoderms, and macroalgae was also higher in lagoons having numerous pinnacles. Canonical correspondence analyses revealed that the distribution and the relative abundance of coral, echinoderm, and macroalgae species were correlated to the relative importance of passes, whereas degree of aperture of the lagoon was also relevant for corals and molluscs. The physical factors that control the processes of water exchange between ocean and lagoon, including passes, submerged reef flats, and spillways, influence the identity and the abundance of most macrobenthic species inside the lagoons

Nutrient fluxes between water column and sediments: Potential influence of the pearl oyster culture

International audienceThis study quantifies benthic nutrient fluxes and sedimentation rates in the Ahe Atoll lagoon (French Polynesia), in two stations located under pearl oyster frames, and two control stations away from the pearl culture facility. Dissolved inorganic nitrogen fluxes ranged between 2 and 35 μmol N m(-2) h(-1) and Soluble Reactive Phosphorus varied between -3 and 8.2 μmol P m(-2) h(-1). Particulate sedimentation rates beneath the oysters were approximately five times higher than in the control zone and the percentage of small particles (≤63μm) were about the twice. In contrast, sediment composition was similar under and outside the direct influence of oyster frames. In this ecosystem, where primary production is dependent on the available nitrogen, our study revealed that, while highly variable, benthic fluxes could sometimes contribute up to 28% of the nitrogen demand for primary production

Affinities of sponges (Porifera) of the Marquesas and Society Islands, French Polynesia

This article reports on a survey of sponges from the higher-island reefs and slopes of the Marquesas and Society Islands archipelagos, French Polynesia, recording presence/absence and an estimate of local abundance at 109 sites from six and eight islands within each archipelago, respectively. Sponge distributions within archipelagos were relatively homogeneous, showing some differential patterns in affinities between north-south islands, and approximately one-third of the fauna apparently endemic to these archipelagos, but between-archipelago comparisons showed large heterogeneity, with only four of the 75 species shared between both archipelagos. The fauna of the Marquesas Islands (with sites consisting mostly of rocky slopes) was dominated by species in order Poecilosclerida and showed a range of taxonomic diversity similar to that of the remote fauna of the Hawaiian Islands. By comparison, the sponge fauna of the Society Islands sites was dominated by species of order Dictyoceratida, reflecting predominance of coral reef and lagoon sites and associated phototrophic feeding strategies. Parsimony and multivariate statistical analyses comparing French Polynesian sponge faunas with others in the southwestern Pacific showed closest nested faunal similarities between the (Marquesas Islands + Society Islands), (((Tonga + Fiji) + Vanuatu) + New Caledonia), and (North Great Barrier Reef + South Great Barrier Reef) but no or very low similarity between more geographically isolated faunas such as Palau and the collective Great Barrier Reef