Temporal and spatial variation in the d¹⁵N and d¹³C of coral tissue and zooxanthellae in Montastraea faveolata collected from the Florida reef tract
Swart, Peter K., Amel Saied, and Kathryn Lamb
Limnol. Oceanogr., 50(4), 2005, 1049–1058

Tissues were collected from Montastraea faveolata at five locations on the Florida Reef tract representing both nearshore and offshore environments. The tissue and zooxanthellae were removed from the skeletons, separated, and subsequently analyzed for d¹⁵N and d¹³C. The mean d¹⁵N value in the coral tissue was +6.6 (±0.6‰) while the d¹³C was -13.3 (±0.5‰) (n = 197). The d¹⁵N and d¹³C of the zooxanthellae were +4.7 (±1.1‰) and -12.2 (±1.0‰), respectively (n = 147). The differences in the d¹⁵N and d¹³C between the zooxanthellae and the tissue were statistically significant. No statistically significant differences were observed between nearshore and offshore stations in either d¹⁵N or d¹³C. The absence of a difference casts doubt on both whether the d¹⁵N of the coral tissues is related to anthropogenic influences and/or whether the d¹⁵N value itself can be used as an indicator of sewage contamination in corals. Between 1995 and 1997, there was an increase of 1‰ in the d¹³C and a decrease of approximately 0.8‰ in the d¹⁵N. The increase in the d¹³C of the organic material was mimicked in the d¹³C of the skeletal material from corals from two reefs in the area. There appears to be clear seasonal variations in the d¹³C of the coral tissue at certain locations with d¹³C of the coral tissues and the zooxanthellae becoming more positive between July and August. The difference between the d¹³C of the zooxanthellae and the coral tissue varies seasonally with the maximum difference occurring in July of each year. In contrast, the maximum d¹³C in the skeleton appears to occur later in the year, between September and November.