Articles | Volume 12, issue 20
Biogeosciences, 12, 6235–6249, 2015
Biogeosciences, 12, 6235–6249, 2015

Research article 30 Oct 2015

Research article | 30 Oct 2015

Water quality, isoscapes and stoichioscapes of seagrasses indicate general P limitation and unique N cycling in shallow water benthos of Bermuda

J. W. Fourqurean2,1, S. A. Manuel3, K. A. Coates3, W. J. Kenworthy4, and J. N. Boyera,2 J. W. Fourqurean et al.
  • 1Marine Science Program, Department of Biology, Florida International University, Miami, Florida, USA
  • 2Southeast Environmental Research Center, Florida International University, Miami, Florida, USA
  • 3Applied Ecology Section, Department of Conservation Services, Bermuda Ministry of Health, Seniors and Environment, Hamilton Parish, Bermuda
  • 4Center for Coastal Fisheries and Habitat Research, NCCOS, NOS, NOAA, Beaufort North Carolina, USA
  • anow at: Center for the Environment and Department of Environmental Science and Policy, Plymouth State University, Plymouth, New Hampshire, USA

Abstract. Striking spatial patterns in stable isotope ratios (isoscapes) and elemental ratios (stoichioscapes) of seagrass leaves and the water column nutrients indicate general P-limitation of both water column and benthic primary productivity on the Bermuda Platform, and they highlight the role of the Bermuda Islands as a source of N and P. We found consistent differences among the four seagrass species (Syringodium filiforme, Thalassia testudinum, Halodule sp. and Halophila decipiens) in the N, P, δ13C and δ15N of leaf tissues. The δ15N of seagrass leaves was especially variable, with values from −10.1 to 8.8 ‰, greatly expanding the reported range of values for all seagrass species globally. Spatial patterns from both the water column and the seagrass leaves indicated that P availability was higher near shore, and δ15N values suggest this was likely a result of human waste disposal. Spatially contiguous areas of extremely depleted seagrass 15N suggest unique N sources and cycling compared to other seagrass-dominated environments. Seagrass N : P values were not as far from the stoichiometric balance between N and P availability as in the water column, and there were no strong relationships between the water column N : P and the seagrass N : P. Such isoscapes and stoichioscapes provide valuable ecogeochemical tools to infer ecosystem processes as well as provide information that can inform food web and animal movement studies.

Short summary
The landscape-scale spatial pattern in the elemental and isotopic composition of organisms offers valuable information about the ecological processes operating across the landscape. When used in parallel, spatial patterns in stable isotopic composition (called isoscapes) and elemental stoichiometry (we propose the term "stoichioscapes") of seagrasses in Bermuda indicate nutrient sources and unique nitrogen cycling on this isolated oceanic platform.
Final-revised paper