HR: 17:45h
AN: B14B-08    [Abstracts]
TI: Stable Oxygen ($\delta^{18}$O) and Carbon ($\delta^{13}$C) Isotopes in the Skeleton of Bleached and Recovering Corals From Hawaii
AU: * Rodrigues, L J
EM: rodrigul@sas.upenn.edu
AF: University of Pennsylvania, Dept. of Earth and Environmental Science 240 South 33rd Street, Philadelphia, PA 19104-6316 United States
AU: Grottoli, A G
EM: grottoli@sas.upenn.edu
AF: University of Pennsylvania, Dept. of Earth and Environmental Science 240 South 33rd Street, Philadelphia, PA 19104-6316 United States
AB: Coral skeletal stable oxygen isotopes ($\delta^{18}$O) reflect changes in seawater temperature and salinity, while stable carbon isotopes ($\delta^{13}$C) reflect a combination of both metabolic (photosynthesis and feeding) and kinetic fractionation. Together, the two isotopic signatures may be used as a proxy for past bleaching events. During bleaching, increased seawater temperatures often contribute to a decline in zooxanthellae and/or chlorophyll concentrations, resulting in a decrease in photosynthesis. We experimentally investigated the effect of bleaching and subsequent recovery on the $\delta^{13}$C and $\delta^{18}$O values of coral skeleton. Fragments from two coral species ({\it Montipora capitata} and {\it Porites compressa}) from Kaneohe Bay, Hawaii were bleached in outdoor tanks by raising the seawater temperature to 30$\deg$C. Additional fragments from the same parent colonies were maintained at ambient seawater temperatures (27$\deg$C) in separate tanks as controls. After one month in the tanks, a subset of the fragments was frozen and all remaining fragments were placed back on the reef to recover. All coral fragments were analyzed for their skeletal $\delta^{13}$C and $\delta^{18}$O compositions at five time intervals: before, immediately after, 1.5, 4, and 8 months after bleaching. In addition, rates of photosynthesis, calcification, and heterotrophy were also measured. Immediately after bleaching, $\delta^{18}$O decreased in bleached {\it M. capitata} relative to controls, reflecting their exposure to increased seawater temperatures. During recovery, $\delta^{18}$O values in the treatment {\it M. capitata} were not different from the controls. In {\it P. compressa}, $\delta^{18}$O did not significantly differ in bleached and control corals at any time during the experiment. Immediately after bleaching, $\delta^{13}$C decreased in the bleached fragments of both species relative to controls reflecting decreased photosynthetic rates. However, during recovery $\delta^{13}$C in both species was greater in bleached than control fragments despite photosynthesis remaining low. In recovering {\it M. capitata}, enriched $\delta^{13}$C values may reflect decreased calcification of bleached fragments, while in {\it P. compressa} they may reflect the combination of decreased calcification and decreased heterotrophy of bleached fragments. $\delta^{13}$C of the tissue and zooxanthellae will also be analyzed and should enhance our understanding of the relative contribution of autotrophy and heterotrophy in these species during bleaching and recovery.
DE: 4853 Photosynthesis
DE: 4870 Stable isotopes
DE: 4267 Paleoceanography
DE: 1040 Isotopic composition/chemistry
DE: 1050 Marine geochemistry (4835, 4850)
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting