The d13C and d15N of coral tissues have been measured from over 150 different individual specimens of Montastraea faveolata collected from five different reefs representing inshore and offshore localities situated off the Key Largo on the Florida reef tract. The mean d15N values for corals was +6.6 (+/- 0.6 ‰) and for zooxanthellae +4.8 (+/-0.99 ‰). The mean d13C was -13.3 (+/-0.6 ‰) for coral tissue and -12.1 (+/-1.06 ‰) for zooxanthellae. Based on a comparison with previous published nitrogen isotopic data which classified coral reefs into ‘anthropogenic’ influenced and pristine, the data presented in this paper would place these corals in the unaffected category.

The N isotopic composition has been measured in algae associated with outfalls from Miami to North Broward. Although heavy values are found inshore, there is no preferential higher values around the outfalls. The heavy inshore values is probably a refection of the type of material being analyzed. The N isotopic composition of the POM showed no unusual high values.

Nitrogen isotopic composition of the sediments in Florida Bay reflects a variety of processes inlcuding the origin of the nitrogen itself. Principally however the variatiosn are related to the fractionation during transformation processes and during assimilation.