Showing papers by "Jean-Pierre Gattuso published in 1993"

Community metabolism and air-sea C02 fluxes in a coral reef ecosystem (Moorea, French Polynesia)

Abstract: Community metabolism (primary production, respiration and calcification) and air-sea CO2 fluxes of the 'Tiahura barrier reef' (Moorea, French Polynesia) were investigated in November and December 1991 Gross production and respiration were respectively 640.2 to 753 and 590.4 to 641.5 mm01 (02 or CO2) m-' d-l (7.7 to 9.0 and 7.1 to 7.7 g C m-2 d ' ) and the reef displayed a slightly negative excess (= net) production. The contribution of planktonic primary production to reef metabolism was negligible (0.15 ?4, of total gross production). Net calcification was positive both during the day and at night; its daily value was 243 mm01 CaCO, m-2 d ' (24.3 g CaC03 m m 2 d-l). Reef metabolism decreased seawater total CO2 by 433.3 mm01 m-d-' The air-sea CO, fluxes were close to zero in the ocean but displayed a strong daily pattern at the reef front and the back reef. Fluxes were positive (COz evasion) at night, decreased as irradiance increased and were negative during the day (COz invasion) Integration of the fluxes measured during a 24 h experiment at the back reef showed that the reef was a source of CO2 to the atmosphere (1 5 minol m-2 d-l).

Depth- and light-dependent variation of carbon partitioning and utilization in the zooxanthellate sclerac-tinian coral Stylophora pistillata

Abstract: This study investigated the effect of light on the short-term metabolic fate of I4C-bicarbonate in zooxanthellae and animal tissue of the coral Stylophora pistillata (Esper, 1797) and on the specific activity of host enzymes involved in the metabolism of carbon. Short-term incubations of coral colonies were carned out In sltu at Bowl Reef (Great Barrier Reef, Australia) at depths of 5 and 30 m to measure rates of oxygen production and consumption and rates of 14C flxation Short-term 14C incubation experiments were also carried out under controlled conditions In the laboratory. Additional samples were collected from 5, 10, 15 and 20 m at Chicken Reef (GBR) to de te rmne the specific enzyme act~vity of coral tlssues from different depths in the water column Light and depth both affected the distribution of 'v anlong photosynthetic products but neither affected translocation rate measured by the In vlvo method (60.4%). The majority of the I4C label was recovered in lipid (33 to 94 %) and watersoluble fractions (5 to 67 The zooxanthellae incorporated more 14C into lipids than into watersoluble compounds (88 to 94 % vs 4 to 7 %) whlle the animal exhibited higher I4C levels in water-soluble compounds than In lipids (44 to 67 % vs 33 to 56 %). Algal fractions showed decreased I4C incorporation into lipids and increased I4C incorporation into water-soluble compounds with increasing depth or decreasing irradiance. The spec~flc activlty of 3-hydroxyacyl CoA dehydrogenase increased with depth supporting the hypothesis that lipids are being catabolized more rapidly at greater depths Citrate synthase and hexokinase activities also decreased with depth The decrease in cytochrome oxidase act~vity wlth depth 1s consistent with a concomitant decrease in respirat~on as depth increases. These results confirm that the carbon cycling In S. plstlllata is partially dependent on light.