%0 Journal Article %J Science of The Total Environment %D 2015 %T Spatio-temporal variations in the composition of organic matter in surface sediments of a mangrove receiving shrimp farm effluents (New Caledonia) %A Adélaide Aschenbroich %A Cyril Marchand %A Nathalie Molnar %A Jonhatan Deborde %A Cédric Hubas %A Hervé Rybarczyk %A Tarik Meziane %K Chlorophyll-a %K fatty acids %K Mangrove %K Organic matter %K Shrimp farming %K Stable isotopes %X

In order to investigate spatio-temporal variations in the composition and origin of the benthic organic matter (OM) at the sediment surface in mangrove receiving shrimp farm effluents, fatty acid (FA) biomarkers, natural stable isotopes (δ13C and δ15N), C:N ratios and chlorophyll-a (chl-a) concentrations were determined during the active and the non-active period of the farm. Fatty acid compositions in surface sediments within the mangrove forest indicated that organic matter inputs varied along the year as a result of farm activity. Effluents were the source of fresh particulate organic matter for the mangrove, as evidenced by the unsaturated fatty acid (UFA) distribution. The anthropogenic \{MUFA\} 18:1ω9 was not only accumulated at the sediment surface in some parts of the mangrove, but was also exported to the seafront. Direct release of bacteria and enhanced in situ production of fungi, as revealed by specific FAs, stimulated mangrove litter decomposition under effluent runoff condition. Also, microalgae released from ponds contributed to maintain high benthic chl-a concentrations in mangrove sediments in winter and to a shift in microphytobenthic community assemblage. Primary production was high whether the farm released effluent or not which questioned the temporary effect of shrimp farm effluent on benthic microalgae dynamic. This study outlined that mangrove benthic organic matter was qualitatively and quantitatively affected by shrimp farm effluent release and that responses to environmental condition changes likely depended on mangrove stand characteristics.

%B Science of The Total Environment %V 512–513 %P 296 - 307 %G eng %U http://www.sciencedirect.com/science/article/pii/S0048969714017938 %R http://dx.doi.org/10.1016/j.scitotenv.2014.12.082 %0 Journal Article %J Environ Sci Pollut Res Int %D 2015 %T The three steps of the carbonate biogenic dissolution process by microborers in coral reefs (New Caledonia). %A Grange, J %A Hervé Rybarczyk %A Tribollet, A %X

Biogenic dissolution of carbonates by microborers is one of the main destructive forces in coral reefs and is predicted to be enhanced by eutrophication and ocean acidification by 2100. The chlorophyte Ostreobium sp., the main agent of this process, has been reported to be one of the most responsive of all microboring species to those environmental factors. However, very little is known about its recruitment, how it develops over successions of microboring communities, and how that influences rates of biogenic dissolution. Thus, an experiment with dead coral blocks exposed to colonization by microborers was carried out on a reef in New Caledonia over a year period. Each month, a few blocks were collected to study microboring communities and the associated rates of biogenic dissolution. Our results showed a drastic shift in community species composition between the 4th and 5th months of exposure, i.e., pioneer communities dominated by large chlorophytes such as Phaeophila sp. were replaced by mature communities dominated by Ostreobium sp. Prior the 4th month of exposure, large chlorophytes were responsible for low rates of biogenic dissolution while during the community shift, rates increased exponentially (×10). After 6 months of exposure, rates slowed down and reached a "plateau" with a mean of 0.93 kg of CaCO3 dissolved per m(2) of reef after 12 months of exposure. Here, we show that (a) Ostreobium sp. settled down in new dead substrates as soon as the 3rd month of exposure but dominated communities only after 5 months of exposure and (b) microbioerosion dynamics comprise three distinct steps which fully depend on community development stage and grazing pressure.

%B Environ Sci Pollut Res Int %8 2015 Jan 17 %G eng %R 10.1007/s11356-014-4069-z