Proceedings of the 8th international coral reef symposium

Pinnacles are a common feature of many lagoons. We investigated their influence on the water chemistry in the lagoon of Tikehau atoll, French Polynesia. Concentration of O2, alkalinity, particulate organic matter and nutrients were measured upstream and downstream of water flowing past a representative coral head. A decalcification rate of -37 g CaCO3/m2/day was calculated. No excess pinnacle production was noted. The gross primary production by the pinnacle community was estimated to be 4 gC/m2/day. (Résumé d'auteur

Satellite-Measured Phytoplankton and Environmental Factors in North Patagonian Gulfs

Abstract An extensive series of high-resolution satellite images from the Sea-Viewing Wide Field-of-View Sensor (SeaWiFS, 2000?2006) was used in thecharacterization of the phytoplankton biomass seasonal cycle of the north Patagoniangulfs (NPG). The NPG system is formed by the San Matías, San José, and Nuevogulfs (between 40°47′and 43°00′S and 63°00′ and 65°1.2′W) and is an area ofecological importance and of great significance for marine conservation in thePatagonian Argentinean Shelf. The spatio temporal variability of phytoplanktonbiomass in each of these environments was characterized by chlorophyll a datafrom satellite images (Chla-sat). The observed seasonal variability was explainedby factors influencing the growth of phytoplankton: photosynthetically availableradiation (PAR from the SeaWiFS sensor) and sea surface temperature (SST fromthe Advanced Very High-Resolution Radiometer, AVHRR). In situ temperature,nutrient, and chlorophyll a concentration data from oceanographic cruises carriedout in Nuevo (four cruises: 1982?1983), San José (four cruises: 1984?1985), andSan Matías (four cruises: 1986?1994) gulfs were also used to explain the observedpatterns. Cycles of phytoplankton and SST over the NPG are typical of temperatewaters. However, Chla-sat cycles were different among gulfs. At the same time,Chla-sat cycles over the gulfs were different from that over the adjacent middlecontinental shelf. SMG was characterized by a bimodal cycle, although in wintermean values were higher than the mean concentration for the whole area. SJG wascharacterized by a unimodal cycle with relatively high values of chlorophyll aconcentration in spring-summer. NG showed a bimodal cycle with maximum valuesin autumn and spring and minimum values in winter and summer. Particularities ofeach gulf are discussed in relation to the seasonal hydrographic characteristics ofthe water column (temperature and nutrients) and in the context of the Patagonianshelf ecosystem.Fil: Williams, Gabriela Noemí. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico; ArgentinaFil: Solis, Miriam Edith. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico; ArgentinaFil: Esteves, Jose Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico; Argentin

Biogeochemical responses following coral mass spawning on the Great Barrier Reef: pelagic-benthic coupling

This study quantified how the pulse of organic matter from the release of coral gametes triggered a chain of pelagic and benthic processes during an annual mass spawning event on the Australian Great Barrier Reef. Particulate organic matter (POM) concentrations in reef waters increased by threefold to 11-fold the day after spawning and resulted in a stimulation of pelagic oxygen consumption rates that lasted for at least 1 week. Water column microbial communities degraded the organic carbon of gametes of the broadcast-spawning coral Acropora millepora at a rate of > 15% h(-1), which is about three times faster than the degradation rate measured for larvae of the brooding coral Stylophora pistillata. Stable isotope signatures of POM in the water column reflected the fast transfer of organic matter from coral gametes into higher levels of the food chain, and the amount of POM reaching the seafloor immediately increased after coral spawning and then tailed-off in the next 2 weeks. Short-lasting phytoplankton blooms developed within a few days after the spawning event, indicating a prompt recycling of nutrients released through the degradation of spawning products. These data show the profound effects of coral mass spawning on the reef community and demonstrate the tight recycling of nutrients in this oligotrophic ecosystem

High rates of nitrogen fixation (acetylene reduction) on coral skeletons following bleaching mortality

Nubbins of the coral Acropora aspera were artificially bleached and nitrogen fixation ( acetylene reduction) rates were measured on the developing epilithic communities. Seasonal comparisons were made between corals that died in summer of heat stress and corals that died in winter from natural cold stress. Rates of acetylene reduction from artificially bleached corals peaked at 26.66 nmol cm(-2) h(-1) 2 weeks after summer mortality, while rates from natural winter mortality peaked at 18.07 nmol cm(-2) h(-1) 12 days after coral death. Comparative rates of acetylene reduction taken from live corals and coral rubble ranged between 0.56 and 1.16 nmol cm(-2) h(-1), and 0.15 and 12.77 nmol cm(-2) h(-1), respectively. N-2-fixation rates from dead corals were up to 30 times greater than those measured on live corals. The observed increase in N-2-fixation from dead corals may increase the availability of nitrogen for use in trophic processes within the reef for an extended period following the initial mortality event. If the spatial scale over which coral mortality has occurred in past thermal bleaching events is considered the ramifications of such an increase may be substantial