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

• Main Authors: J. W. Fourqurean, S. A. Manuel, K. A. Coates, W. J. Kenworthy, J. N. Boyer
• Format: Article
• Language: English
• Published: Copernicus Publications 2015-10-01
• Series: Biogeosciences
• Online Access: http://www.biogeosciences.net/12/6235/2015/bg-12-6235-2015.pdf
• ISSN: 1726-4170; 1726-4189

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 (<i>Syringodium filiforme</i>, <i>Thalassia testudinum</i>, <i>Halodule</i> sp. and <i>Halophila decipiens</i>) in the N, P, &delta;¹³C and δ¹⁵N of leaf tissues. The δ¹⁵N of seagrass leaves was especially variable, with values from −10.1 to 8.8 &permil;, 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.