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

Abstract

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 penod, 5 closely spaced and shallow subt~dal coral colonies were cored at 1 mo ~ntervals. These cores were subsequently analysed to determine linear extension (growth) and thc 0:-C and 6180 of each monthly growth increment. Environn~ental 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 reglon. Of the 3 skeletal attributes considered in t h ~s study, s k e l ~t a l 6180 showed the strongest correlation with thls seasonal cyc!e. The se~cena! v~I.l:;l!itins 111 ~ke!ets! 6'" are irtt.rihu!ec! tn change< i n SST [acroi~ntinrj for ca 60% of the 6' " signal) and inferred changes in water isotopic composition due to rainfall and runoff (ca 4 0 % of the SI80 signal). Although these results indicate that this coral is capable of yielding highresolution paleoenvironmental records from retrospective analysis of the skeleton, there were sig.nificant and unexplained between-colony differences in mean Sl80. Therefore, for this species of coral in this setting, great care must be taken before interpreting the regional environmental sign~f~cance of either gradual changes in mean 6180 through the length of a single long coral core, or differences between modern and ancient (fossil) colonies. Although skeletal 6I3C 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.