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Multiple-use marine protected areas (MPAs) are used to manage marine resources, allocate space to different users and reduce conflicts while protecting marine biodiversity. In the Mediterranean, MPA managers are increasingly interested in containing the effects of coastal recreation within underwater trails, but snorkelers impacts on the surrounding ecosystem remain largely unknown. In a Mediterranean MPA, an underwater snorkeling trail was established to concentrate snorkelers and increase their awareness of marine habitats and species. The high level of summer frequentation may have negative impacts on the surrounding environment through trampling on the sessile flora or disturbance to the vagile fauna. We used a before-after-control-impact (BACI) design to analyse these potential human impacts. The structure of macroalgae and fish assemblages were used as indicators. Permutational multivariate analyses of variance (PERMANOVA) were carried out to assess potential temporal and spatial changes of the indicators between the trail and a control location within the adjacent no-take/no-use area. Fish communities and macroalgae were subjected to natural temporal trends but no significant impacts of snorkelers were found. Four reasons could explain the absence of snorkelers impact on the surrounding marine environment: (1) the absence of very fragile organisms within the trail (and the control no-take/no-use area) such as gorgonians or bryozoans; (2) the life cycle of the algae with a natural decreasing trend in summer, corresponding to the trail opening period; (3) only a few snorkelers are practicing apnoea; and (4) the information at the entrance and along the trail may influence the snorkelers’ behaviour.

Coral reefs in French Polynesia, just like many others throughout the world, have been subjected to several natural disturbances including 15 cyclones, seven major bleaching events, and several Acanthaster planci outbreaks since the 1980s. In order to document the effects of these perturbations on coral assemblages, we initiated a long-term monitoring program that extended over both local and regional scales. Coral cover was quantified at 20 sites situated on the outer reef slope of 13 islands. The results from the first decade (1992-2002) are analyzed and the adequacy of our approach is discussed in the context of identifying potential indicators of coral reef health. Among 13 islands in French Polynesia, only two were unaffected by natural disturbances. We found important local and regional variation in the impacts of coral bleaching and cyclones, and three major temporal trends were distinguished: 1) 10 sites where coral cover decreased in relation to the occurrence of major disturbances; 2) nine sites where coral cover increased, despite the occurrence of disturbances affecting seven of them; and 3) a site where no significant variation in coral cover was found. The responses to perturbations were different among coral genera: Acropora species were particularly susceptible to bleaching events, whereas physical damages induced by cyclones concerned mainly branching species of Acropora and Pocillopora. Thus, monitoring surveys could be improved by selecting different and complementary indicators (one on the variation in diversity, one estimating changes in the abundance/cover, and one estimating the potential for recovery), by integrating several spatial scales, and by including at least the most informative species. High frequency recordings of environmental parameters (e.g. sea surface temperature) may be also a complementary tools for identifying causal relationships between changes in coral reef community structure and the factors causing the changes.

The spatial variability of the biogeochemical composition of surface sediments was investigated around Moorea, French Polynesia. This study complements other ones conducted in Moorea to assess coral reef ‘‘health’’. A total of 35 stations were sampled at four sites around the island, on the following geomorphological units: fringing reef of the bays, fringing reef of the lagoon, channel, barrier reef, pass, sandy slope, bay bottom. We found strong spatial heterogeneity in the biogeochemical composition of surface sediments. The multivariate analyses (PCA and clustering) distinguished four major sediment types around Moorea, and a gradient between the bayheads and the bay entrances. The first type corresponds to the inner half bay bottoms, and clearly represents the ‘‘terrigeneous’’ influence. This terrigeneous sediment type was mainly characterised by a clear deficit in carbonates and, conversely, by an enrichment in organic compounds (organic carbon (OC), nitrogen (N), as well as total amino acids (AA) and carbohydrates (CH) in mg g � 1 ) that were highly degraded. Two other sediment types were influenced by the carbonated reef system. They were highly carbonated (inorganic carbon (IC) around 11%; i.e., carbonates around 90%), and showed low organic compound concentrations. They were also characterised by high hydrolysable organic carbon (HOC) concentrations. These two ‘‘reef-characteristic’’ sediment types can be distinguished by their N concentrations and C/N ratio. The fourth type represents a transition between ‘‘reef-characteristic’’ and ‘‘terrigeneous’’ sediment types. Our results showed that HOC, total AA and CH, examined for the first time in coral reef ecosystems, were reliable descriptors for spatial variability surveys, together with the more ‘classical’ descriptors: IC, OC and N. 2004 Elsevier Ltd. All rights reserved.

The export of carbon and carbonate from coral reefs was investigated through a multidisciplinary investigation of the hydrological, geochemical, sedimentological and biological features of Tiahura reef on the northwestern coast of Moorea Island (French Polynesia). The hydrology of the fore-reef is characterised by prevailing longshore western currents and a strong thermocline. As revealed by turbidity structures (benthic and intermediate nepheloid layers) and by the amount of particles collected by near-bottom sediment traps, horizontal and downslope advections of particles dominate over offshore vertical transport. The exported material is rich in carbonate (ca. 80%) and poor in organic matter (ca. 4%). Sedimentation rates at 430 m depth, i.e. definitive export, reached 209.6 mg m-2 d-1 (dry weight). Estimates of carbon and carbonates export for Tiahura reef also reported here represent respectively 47% and 21% of the organic and inorganic carbon produced within the reef.