Macroalgae as a tool for assessing the ecological status of coral reefs under the Water Framework Directive: A case study on the reef flats of La Réunion (Indian Ocean).

The monitoring of macroalgae is required by the Water Framework Directive (WFD) to achieve good ecological status for coastal waters and specific questions arise for tropical ecosystems belonging to the outermost European regions. To assess the suitability of macroalgae as a biological quality indicator for La Réunion reef flats (France), we performed multivariate analyses linking the abundance and composition of macroalgae to water physico-chemistry. Three hydrological groups of stations were identified according to dissolved inorganic nitrogen (DIN) concentrations and DIN/PO4 ratios. Some indicator species were found at the N-enriched stations (Bryopsis pennata, Caulerpa lamourouxii, Chaetomoropha vieillardii, Derbesia sp., Blennothrix lyngbyacea, Sphacelaria tribuloides), and others at the non-impacted stations (Anabaena sp1, Blennothrix glutinosa, Codium arabicum, Neomeris vanbosseae). Another key result was the significant increase in red algal cover at the most N-enriched station. Our findings are discussed in the context of the application of the WFD in the outermost French regions.

Biodiversity of Pigmented Fungi Isolated from Marine Environment in La Réunion Island, Indian Ocean: New Resources for Colored Metabolites.

Marine ecosystems cover about 70% of the planet surface and are still an underexploited source of useful metabolites. Among microbes, filamentous fungi are captivating organisms used for the production of many chemical classes of secondary metabolites bound to be used in various fields of industrial application. The present study was focused on the collection, isolation, screening and genotyping of pigmented filamentous fungi isolated from tropical marine environments around La Réunion Island, Indian Ocean. About 150 micromycetes were revived and isolated from 14 marine samples (sediments, living corals, coral rubble, sea water and hard substrates) collected in four different locations. Forty-two colored fungal isolates belonging to 16 families, 25 genera and 31 species were further studied depending on their ability to produce pigments and thus subjected to molecular identification. From gene sequence analysis, the most frequently identified colored fungi belong to the widespread Penicillium, Talaromyces and Aspergillus genera in the family Trichocomaceae (11 species), then followed by the family Hypocreaceae (three species). This study demonstrates that marine biotopes in La Réunion Island, Indian Ocean, from coral reefs to underwater slopes of this volcanic island, shelter numerous species of micromycetes, from common or uncommon genera. This unstudied biodiversity comes along with the ability for some fungal marine inhabitants, to produce a range of pigments and hues.

Characterization of dissolved organic matter in a coral reef ecosystem subjected to anthropogenic pressures (La Réunion Island, Indian Ocean) using multi-dimensional fluorescence spectroscopy.

La Saline fringing reef is the most important coral reef complex of La Réunion Island (southwestern Indian Ocean; 21°07'S, 55°32'E). This ecosystem is subjected to anthropogenic pressures through river inputs and submarine groundwater discharge (SGD). The goal of this study was to characterize the pool of fluorescent dissolved organic matter (FDOM) in different water bodies of La Saline fringing reef ecosystem using excitation-emission matrix (EEM) spectrofluorometry. From EEMs, we identified the different fluorophores by the peak picking technique and determined two fluorescence indices issued from the literature: the humification index (HIX) and the biological index (BIX). The main known fluorophores were present within the sample set: humic-like A, humic-like C, marine humic-like M, tryptophan-like T1 and T2, and tyrosine-like B1 and B2. In some samples, unknown fluorophores ("U") were also detected. The surface oceanic waters located beyond the reef front displayed a typical oligotrophic marine signature, with a dominance of autochthonous/biological material (presence of peaks: T1>B1>A>T2>M>C; HIX: 0.9±0.4; BIX: 2.3±1.1). In the reef waters, the autochthonous/biological fingerprint also dominated even though the content in humic substances was higher (same relative distribution of peaks; HIX: 1.6±0.6; BIX: 1.0±0.1). Sedimentary and volcanic SGD showed very different patterns with a strong terrestrial source for the former (A>T1>C>B1 and A>C>B1; HIX: 9.8±2.0; BIX: 0.8±0.0) and a weak terrestrial source for the latter (A>B1>U3>B2>C and A>U4>C; HIX: 2.4±0.3; BIX: 0.9±0.0). In the Hermitage River, both humic substances and protein-like material were abundant (T1>A>U5>B1>C>B2; HIX: 2.3; BIX: 1.4). We provide evidences for the presence of anthropogenic DOM in some of these water bodies. Some oceanic samples (presence of peaks U1 and U2) were likely contaminated by oil-derived PAHs from ships navigating around the reef front, whereas the Hermitage River was highly impacted by sewage effluents, numerous in this coastal area of La Réunion Island. We conclude that multi-dimensional fluorescence spectroscopy (EEM) coupled to the determination of HIX and BIX is a good tool for assessing the origin and distribution of DOM in the coral reef ecosystems submitted to anthropogenic impacts.

AChE and EROD activities in two echinoderms, Holothuria leucospilota and Holoturia atra (Holothuroidea), in a coral reef (Reunion Island, South-western Indian Ocean).

AChE and EROD activities were investigated in two holothurian species, Holothuria leucospilota and Holoturia atra, from a tropical coral reef. These organisms were collected from 3 back-reef stations, where temperature and salinity were homogeneous. The activity levels of both AChE and EROD varied significantly between the two species, but were in the range of values determined in other echinoderm species. AChE activity levels were higher in the longitudinal muscle than in the tentacle tegument. Among the several tissues tested, the digestive tract wall exhibited higher EROD activity levels. Sex did not influence AChE and EROD activity levels in both species. Animal biomass and EROD activity levels were only correlated in the tegument tissue of H. atra, and we hypothesize a possible influence of age. EROD activity did not show intraspecific variability. A significant relationship was found between AChE activity and Cuvierian tubules time of expulsion in Holothuria leucospilota. Individuals collected at the southern site presented both lower AChE activity levels and Cuvierian tubules time of expulsion, indicating possible neural disturbance. More information on holothurians biology and physiology is needed to further assess biomarkers in these key species. This study is the first of its kind performed in the coastal waters of Reunion Island and data obtained represent reference values.

Low community photosynthetic quotient in coral reef sediments.

Fluxes of dissolved inorganic carbon and oxygen at the water-sediment interface were measured at eight coral reef stations (Indian Ocean) in summer and winter. The dark fluxes provided the community respiratory quotient (CRQ = dissolved inorganic carbon release / oxygen uptake) and the diurnal fluxes corrected from the dark fluxes gave the community photosynthetic quotient (CPQ = oxygen gross release / dissolved inorganic carbon gross uptake). The CRQ and the winter CPQ were not significantly different from 1. Summer CPQ (0.79; SD 0.02) was significantly lower than 1 due to the combined effect of the daily evolution of the community respiration and the discrepancy between the daily evolution in community oxygen respiration and community carbon respiration. These results highlight the importance of measuring simultaneously the benthic community production and respiration for long term integrated data sets, instead of the traditional daily or seasonal budget calculations from limited measures of community respiration.