Pascale Cuet

Seasonal coupling and de‐coupling of net calcification rates from coral reef metabolism and carbonate chemistry at Ningaloo Reef, Western Australia

Rates of net production, net calcification, and nutrient uptake were measured in a coral-dominated reef flat community on Ningaloo Reef in northwestern Australia under seasonally minimum and maximum light levels. Daily integrated light decreased twofold while water temperatures remained relatively constant increasing by only 1°C on average from summer to winter. Rates of daily community gross primary production (GPP) were only 33% ± 9% higher in summer than in winter (1400 ± 70 versus 1050 ± 60 mmol C m−2 d−1), far less than the twofold seasonal changes reported for most shallow reef communities. Rates of daily community net calcification (Gnet) were not significantly different between seasons (190 ± 40 mmol CaCO3 m−2 d−1 in summer versus 200 ± 10 mmol CaCO3 m−2 d−1 in winter). The average rate of total nitrogen uptake (dissolved + particulate) was also not significantly different between summer and winter (8.3 ± 3.8 versus 6.6 ± 3.4 mmol N m−2 d−1, respectively), despite evidence of sporadically high nitrate uptake in both seasons. In summer, rates of hourly net calcification (gnet) were linearly correlated with diurnal changes in net production, pH, and aragonite saturation state (Ωar); and were mostly correlated with light except at mid-day under heavy cloud cover. However, in winter,gnet was independent of diurnal changes in light, net production, pH, and Ωar indicating that the reef flat community had possibly reached a threshold above which rates of net calcification were insensitive to diurnal changes in their environment.

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.

Hydrocarbons in a coral reef ecosystem subjected to anthropogenic pressures (La Réunion Island, Indian Ocean)

The La Saline fringing reef, which is the most important coral reef complex of La Reunion Island, (south- western Indian Ocean), is subjected to anthropogenic pressures through river and groundwater inputs. Salinity and biogeochemicalparameters(silicates,nitrates,dissolvedorganiccarbon,chlorophyll-a),aswellasaliphatichydrocarbons (AHs) and polycyclic aromatic hydrocarbons (PAHs) were analysed in particulate and dissolved material from ground- waters,rivers,harbour,backreef,forereefandoceanicwatersintheLaSalinereefareaduringtherainyseason(February- March 2012). Particulate and dissolved AH concentration ranges were 0.07-144 and 0.06-0.58 m gL � 1 respectively. Particulate and dissolved PAH concentrations ranges were 4.3-326 and 28-350 ng L � 1 respectively. AHs, dominated by nC15, nC17, nC18 compounds or nC26, nC27, nC29, nC31 compounds, were mainly of biogenic origin (phytoplankton, bacteria, higher-plant debris) although some anthropogenic (petroleum inputs) signatures were recorded in the dissolved phase from the harbour and fore reef areas. PAHs, dominated by two- to three-ring compounds and their alkylated homologues, reflected unburned petroleum inputs, but probably also biogenic sources. From the distribution of salinity, biogeochemical parameters and hydrocarbons, we found that inland waters flowed mainly in the surface and in the southern part of reef waters and that particulate PAHs allowed tracking these inland water intrusions in fore reef waters. Finally, this pilot study highlights the uncoupling between the dynamics of AHs and PAHs in tropical environments. Additionalkeywords: aliphatichydrocarbons,groundwaters,LaSalinefringingreef,polycyclicaromatichydrocarbons, tropical environment.

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.

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.