SEASONAL-VARIATION IN SKELETAL EXTENSION RATE AND STABLE ISOTOPIC (C-13 C-12 AND O-18/O-16) COMPOSITION IN RESPONSE TO SEVERAL ENVIRONMENTAL VARIABLES IN THE CARIBBEAN REEF CORAL SIDERASTREA-SIDEREA/

The potential of the massive reef building coral Siderastrea siderea t o be a reliable archive of past environmental variations was investiga ted by means of a field experiment conducted on a fringing reef in Pan ama. Over a 14 mo experimental period, 5 closely spaced and shallow su btidal coral colonies were cored at 1 mo intervals. These cores were s ubsequently analysed to determine linear extension (growth) and the de lta(13)C and delta(18)O of each monthly growth increment. Environmenta l conditions were recorded continuously by instruments deployed within a distance of 10 to 110 m from the corals. The environmental variable s sea surface temperature (SST), salinity, wind, sun and rainfall were all well correlated with one another, reflecting the dominant seasona l cycle in the region. Of the 3 skeletal attributes considered in this study, skeletal delta(18)O showed the strongest correlation with this seasonal cycle. The seasonal variations in skeletal delta(18)O are at tributed to changes in SST (accounting for ca 60 % of the delta(18)O s ignal) and inferred changes in water isotopic composition due to rainf all and runoff (ca 40% of the delta(18)O signal). Although these resul ts indicate that this coral is capable of yielding high-resolution pal eoenvironmental records from retrospective analysis of the skeleton, t here were significant and unexplained between-colony differences in me an delta(18)O. Therefore, for this species of coral in this setting, g reat care must be taken before interpreting the regional environmental significance of either gradual changes in mean delta(18)O through the length of a single long coral core, or differences between modern and ancient (fossil) colonies. Although skeletal delta(13)C and growth ra te did show some relatively weak but significant correlations with som e of the environmental variables, especially when the records from all colonies were combined, it was concluded that these attributes have r elatively low potential for regional paleoenvironmental reconstruction .