No abstract

International audienceStegastes planifrons and Stegastes adustus are two abundant territorial damselfishes of Caribbean coral reefs. Their trophic niches and their food utilisation on Guadeloupean reefs at two contrasting sites were compared on the basis of stomach content and stable isotope analyses (15N/14N and 13C/12C ratios). While ingested food items slightly differed between species, the assimilation of each food source (macroalgae, turf, benthic invertebrates and detritus) calculated with a concentration-dependent mixing model was similar. Macroalgae, that presented the highest nutritional values, contributed to 33% in biomass of their diet. Invertebrates, algal turf and detritus showed similar nutritional values, while they presented different contributions to the diet of Stegastes. Stable isotope ratios indicated similar fish trophic level and similar isotopic structure on a territory scale, showing a similar trophic niche of the two damselfish at the two sites. However, co-occurrence in the same shallow habitat was associated with a reduction in the size of the territory of S. adustus and an increase in the number of species of macroalgae inside their territory, suggesting spatial competitive interactions

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Chlordecone is an organochlorine pesticide, used in the Lesser Antilles from 1972 to 1993 to fight against a banana weevil. That molecule is very persistent in the natural environment and ends up in the sea with runoff waters. The objective of the present study is to evaluate the level of contamination in several trophic groups of marine animals according to their distance from the source of pollution. Samples of suspended matter, macroalgae, herbivorous fishes, detrivorous crustaceans, zooplanktivorous fishes, first- and second-order of carnivorous fishes, and piscivorous fishes have been collected in two sites, located downstream the contaminated sites (Goyave and Petit-Bourg), in three marine habitats (coastal mangroves, seagrass beds located 1.5 km from the shoreline, and coral reefs at 3 km offshore). Animals collected in mangroves were the most contaminated (mean concentrations 193 μg kg in Goyave and 213 μg kg in Petit-Bourg). Samples from seagrass beds presented intermediate concentrations of chlordecone (85 μg kg in Goyave and 107 μg kg in Petit-Bourg). Finally, samples from coral reefs were the less contaminated (71 μg kg in Goyave and 74 μg kg in Petit-Bourg). Reef samples, collected 3 km offshore, were two to three times less contaminated than those collected in mangroves.

Chlordecone is a persistent organochlorine pesticide used in the banana fields of the French West Indies from 1972 to 1993. Three marine habitats (mangroves, seagrass beds and coral reefs) of two study sites located downstream contaminated rivers were chosen to evaluate the level of contamination of marine food webs. On each habitat, the food chain collected included suspended organic matter, primary producers (macroalgae, algal turf, seagrass), zooplankton, symbiotic organisms (corals, sea anemones), primary consumers (herbivores, suspension feeders, biofilm feeders), omnivores and detritivores (lobsters, fish), secondary consumers (carnivores 1: invertebrate feeders, planktivores) and tertiary consumers (carnivores 2: invertebrate and fish feeders, piscivores). Log-linear regressions of the concentrations of chlordecone versus nitrogen isotopic ratios (δ15N) were used to assess the bioaccumulation of chlordecone along trophic food webs. At each site, bioconcentration and bioamplification take part on the transfer of chlordecone in marine organisms. In mangroves (i.e. close to the source of pollution), lower trophic magnification factors (TMF) indicated that bioconcentration prevailed over bioamplification phenomenon. The opposite phenomenon appeared on coral reefs in which bioconcentration processes were less important and bioamplification pathway became dominant. Far from the source of pollution, molecules of chlordecone seemed to be transfered to organisms mostly via trophic interactions rather than water contact.