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 δ15N and δ13C. The mean δ15N value in the coral tissue was +6.6 (±0.6‰) while the δ13C was -13.3 (±0.5‰) (n = 197). The δ15N and δ13C of the zooxanthellae were +4.7 (±1.1‰) and -12.2 (±1.0‰), respectively (n = 147). The differences in the δ15N and δ13C between the zooxanthellae and the tissue were statistically significant. No statistically significant differences were observed between nearshore and offshore stations in either δ15N or δ13C. The absence of a difference casts doubt on both whether the δ15N of the coral tissues is related to anthropogenic influences and/or whether the δ15N 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 δ13C and a decrease of approximately 0.8‰ in the δ15N. The increase in the δ13C of the organic material was mimicked in the δ13C of the skeletal material from corals from two reefs in the area. There appears to be clear seasonal variations in the δ13C of the coral tissue at certain locations with δ13C of the coral tissues and the zooxanthellae becoming more positive between July and August. The difference between the δ13C of the zooxanthellae and the coral tissue varies seasonally with the maximum difference occurring in July of each year. In contrast, the maximum δ13C in the skeleton appears to occur later in the year, between September and November.