MEPS 166:109-118 (1998)  -  doi:10.3354/meps166109

Seasonal variation in skeletal extension rate and stable isotopic (13C/12C and 18O/16O) composition in response to several environmental variables in the Caribbean reef coral Siderastrea siderea

Héctor M. Guzmán1,*, Alexander W. Tudhope2

1Smithsonian Tropical Research Institute, Unit 0948, APO. AA 34002-0948, USA 2Department of Geology and Geophysics, Edinburgh University, Edinburgh EH9 3JW, Scotland, UK

The potential of the massive reef building coral Siderastrea siderea to be a reliable archive of past environmental variations was investigated by means of a field experiment conducted on a fringing reef in Panama. Over a 14 mo experimental period, 5 closely spaced and shallow subtidal coral colonies were cored at 1 mo intervals. These cores were subsequently analysed to determine linear extension (growth) and the δ13C and δ18O of each monthly growth increment. Environmental conditions were recorded continuously by instruments deployed within a distance of 10 to 110 m from the corals. The environmental variables sea surface temperature (SST), salinity, wind, sun and rainfall were all well correlated with one another, reflecting the dominant seasonal cycle in the region. Of the 3 skeletal attributes considered in this study, skeletal δ18O showed the strongest correlation with this seasonal cycle. The seasonal variations in skeletal δ18O are attributed to changes in SST (accounting for ca 60% of the δ18O signal) and inferred changes in water isotopic composition due to rainfall and runoff (ca 40% of the δ18O signal). Although these results indicate that this coral is capable of yielding high-resolution paleoenvironmental records from retrospective analysis of the skeleton, there were significant and unexplained between-colony differences in mean δ18O. Therefore, for this species of coral in this setting, great care must be taken before interpreting the regional environmental significance of either gradual changes in mean δ18O through the length of a single long coral core, or differences between modern and ancient (fossil) colonies. Although skeletal δ13C and growth rate did show some relatively weak but significant correlations with some of the environmental variables, especially when the records from all colonies were combined, it was concluded that these attributes have relatively low potential for regional paleoenvironmental reconstruction.

Coral skeleton · Stable isotopes · Panama · Reefs

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