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/
Hm. Guzman et Aw. Tudhope, 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/, Marine ecology. Progress series, 166, 1998, pp. 109-118
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
.