Spatial and seasonal variability in elemental content, δ13C, and δ15N ofThalassia testudinum from South Florida and its implications for ecosystem studies

Authors

James W. Fourqurean, Department of Biological Sciences and Southeast Environmental Research Center, Florida International UniversityFollow
Susie Escorcia, Department of Earth Sciences and Southeast Environmental Research Center, Florida International UniversityFollow
William T. Anderson, Department of Earth Sciences and Southeast Environmental Research Center, Florida International UniversityFollow
Joseph C. Zieman, Department of Environmental Sciences, University of VirginiaFollow

Abstract

Elemental and isotopic composition of leaves of the seagrassThalassia testudinum was highly variable across the 10,000 km² and 8 years of this study. The data reported herein expand the reported range in carbon:nitrogen (C:N) and carbon:phosphorus (C:P) ratios and δ¹³C and δ¹⁵N values reported for this species worldwide; 13.2–38.6 for C:N and 411–2,041 for C:P. The 981 determinations in this study generated a range of −13.5‰ to −5.2‰ for δ¹³C and −4.3‰ to 9.4‰ for δ¹⁵N. The elemental and isotope ratios displayed marked seasonality, and the seasonal patterns could be described with a simple sine wave model. C:N, C:P, δ¹³C, and δ¹⁵N values all had maxima in the summer and minima in the winter. Spatial patterns in the summer maxima of these quantities suggest there are large differences in the relative availability of N and P across the study area and that there are differences in the processing and the isotopic composition of C and N. This work calls into question the interpretation of studies about nutrient cycling and food webs in estuaries based on few samples collected at one time, since we document natural variability greater than the signal often used to imply changes in the structure or function of ecosystems. The data and patterns presented in this paper make it clear that there is no threshold δ¹⁵N value for marine plants that can be used as an unambiguous indicator of human sewage pollution without a thorough understanding of local temporal and spatial variability.

Comments

This material is based upon work supported by the National Science Foundation through the Florida Coastal Everglades Long-Term Ecological Research program under Cooperative Agreements #DBI-0620409 and #DEB-9910514. Any opinions, findings, conclusions, or recommendations expressed in the material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

Recommended Citation

Fourquerean, J.W., S.P. Escorcia, W.T. Anderson, J.C. Zieman. 2005. Spatial and seasonal variability in elemental content, d13C and d15N of Thalassia testedinum from south Florida and its implications for ecosystem studies. Estuaries 28 (3): 447-461.