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The nitrogen isotopic composition of a variety of organisms in coral reefs has been used extensively, not only to study nitrogen dynamics, but also as a tracer for the input of anthropogenic nitrogen. However, the interplay between isotopic fractionation associated with the internal
nitrogen cycling and variations in the absolute values supplied by external source signatures is poorly understood. Here we report the δ15N and δ13C of algae, sponges, and fishes, the δ15N and δ18O of dissolved NO3–,
and the δ15N of dissolved organic nitrogen in samples collected from the Florida reef tract over a 2.5-yr period (2003–2005). Our data are synthesized with results from previous studies of the δ15N of particulate organic material and coral tissue and
zooxanthellae from the same area to provide a more detailed understanding of factors controlling coral reef δ15N and variation among biogenic components. These data show that during the study period there were (1) no clear spatial patterns in the δ15N of biogenic
components related to proximity to the Florida Reef tract, and (2) no temporal patterns related to the wet or dry seasons. The range of δ15N and δ13C in the particulate organic material could be best explained as a mixture of material derived from seagrass,
algae, mangroves, and fishes. The δ15N and δ18O of NO3– support a model in which variations in nitrogen isotopic composition are derived mainly from the isotopic effects associated with the nitrification of NH4+
to NO3– and subsequent assimilation by primary producers rather than through the input of isotopically distinct NO3– from external sources.
The Bulletin of Marine Science is dedicated to the dissemination of high quality research from the world's oceans. All aspects of marine science are treated by the Bulletin of Marine Science, including papers in marine biology, biological oceanography, fisheries, marine affairs, applied marine physics, marine geology and geophysics, marine and atmospheric chemistry, and meteorology and physical oceanography.