Temporal and spatial variation in the d15N and d13C of coral tissue and zooxanthellae in Montastraea faveolata collected from the Florida reef tract
Limnol. Oceanogr., 50(4), 2005, 1049-1058 | DOI: 10.4319/lo.2005.50.4.1049
Abstract: 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 
15N and 13C. The mean 15N value in the coral tissue was +6.6 (±0.6‰) while the 13C was -13.3 (±0.5‰) (n = 197). The 15N and 13C of the zooxanthellae were +4.7 (±1.1‰) and -12.2 (±1.0‰), respectively (n = 147). The differences in the 15N and 13C between the zooxanthellae and the tissue were statistically significant. No statistically significant differences were observed between nearshore and offshore stations in either 15N or 13C. The absence of a difference casts doubt on both whether the 15N of the coral tissues is related to anthropogenic influences and/or whether the 15N 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 13C and a decrease of approximately 0.8‰ in the 15N. The increase in the 13C of the organic material was mimicked in the 13C of the skeletal material from corals from two reefs in the area. There appears to be clear seasonal variations in the 13C of the coral tissue at certain locations with 13C of the coral tissues and the zooxanthellae becoming more positive between July and August. The difference between the 13C of the zooxanthellae and the coral tissue varies seasonally with the maximum difference occurring in July of each year. In contrast, the maximum 13C in the skeleton appears to occur later in the year, between September and November.