Impact of Nutrients on Reefs in the Florida Keys

Integrated Florida Reef Tract

Project Title	1.2. Impact of Nutrients on Reefs in the Florida Keys
Key Investigators	Peter K Swart and Kathryn Lamb
Project Duration	December 15, 1999 – December 14, 2003
OBJECTIVE(S)	The objectives of this research are to i) document temporal and spatial patterns of variations in the stable N isotopic composition of organisms in the Florida Keys, ii) document the variations in the sources of inorganic and organic nitrogen which are inputted into the Florida Keys form anthropogenic and natural sources, and iii) construct a model for the cycling of nitrogen in the Florida Keys
SUMMARY	Dissolved Inorganic Nitrogen Species (DIN) A new bacterial method (Sigman et al 2001 and Casciotti et al.2002) is being employed for the analysis of the nitrogen isotopic concentration of nitrate in waters found in the Florida Keys, which typically have concentrations less than 1M. Water for isotopic analysis has been collected from stations with varying depths from cruises off the Florida reef tract made during June, August, October, December 2000, February, June, August, November 2001, and February, April, June, August, October, and December 2002. These samples have been analyzed for their nitrate concentration and samples collected during 2002 will be processed according to the new bacterial method Particulate Organic Material (POM): The nitrogen and carbon isotopic composition of the particulate organic matter has also been analyzed from samples collected on the above-mentioned cruises. The POM data show highly varied patterns of Δ¹⁵N and there is seemingly no correlation between Δ¹⁵N values and any sort of cyclic seasonal patterns of Δ¹⁵N composition. It is possible that a portion of the signal may be due in part to upwelling of deep nutrient rich waters off the coast, but this hypothesis is still being explored. Algal and Sea Grass Material: Over 100 samples of macro and turf algae, as well as sea grasses have been collected from the Pennekamp State Park, Florida Keys National Marine Sanctuary and analyzed for the carbon and nitrogen isotopic composition. Preliminary results show that the inshore reefs had an elevated Δ¹⁵N signal, as compared to the offshore reefs, which is often cited as an indicator of anthropogenic waste. However, when looking at a single transect line from inshore to offshore, the ¹⁵N values show no definitive trend which may indicate a mixing of different nutrient sources. Herbivorous Fish: The carbon and nitrogen isotopic composition has been measured on approximately 75 herbivorous fish muscle tissue from the FKNMS. Tissue sampled in the show a similar trend of heavy Δ¹⁵N values on more inshore reefs and lighter values on the more offshore reefs. At this point in time, however, we are working towards expanding the breadth of focus to include piscivores fish as an additional point of comparison. Further assessments are currently being investigated and will be reported in the near future. Corals: Stable N isotopic analysis of coral tissues and zoozanthellae revealed them to have a normal range of values.
PUBLICATION(S)	Lamb, K.A., Swart, P.K., and Ellis, G.S. (2002) Insights into Nitrogen Isotope Fractionation in Coral Reefs, Eos. Trans. AGU, vol.83, no.47, Fall Meeting Suppl., Abstract B71A-0718 Lamb, K.A., Swart, P.K., and Ellis, G.S. (2002) A detailed study of the nitrogen isotopic composition of organic and inorganic nitrogen in a coral reef environment, Proceedings from 2002 Ocean Sciences Meeting, American Geophysical Union, vol.83, no.4. Ellis, G., Moses, C., Swart, P.K., and Milne, P. (2000) Contributions of natural and anthropogenic nitrogen in the Florida Keys reef tract using stable isotope composition and natural sterol concentration, GSA Abstracts with Programs, p. 102.