Significant nutrient co-limitation across a diversity of mangrove-dominated estuaries in the Bahamas

Jacob E. Allgeier¹⁺, Amy D. Rosemond¹, Craig A. Layman^2
1Odum School of Ecology, University of Georgia
²Marine Sciences Program, Florida International University
⁺ contact info: jeallg@uga.edu, 706-542-5881
Nitrogen (N) and phosphorus (P) are critical limiting factors for primary production, and thus their relative availability can affect food web structure and function, biodiversity and net ecosystem productivity.  Coastal ecosystems, as hot spots for urbanization and resulting land-use changes, and the recipient of excessive ‘down-stream’ nutrient loading, are of particular research interest because of the extensive ecological services they provide.  Here we used observational (seagrass nutrient content) and experimental (nutrient diffusing substrates; NDS) methodologies to examine nutrient limitation across a spatial gradient of relatively pristine (n=3) and hydrologically fragmented (n=4) mangrove estuaries in the Bahamas.   We tested 1) whether nutrient limitation varied among and within pristine estuaries and 2) whether ecosystem fragmentation affected limitation.  Our results showed that all estuaries, regardless of degree of fragmentation were significantly co-limited by N and P (exhibiting large increases in biomass in response to N+P additions compared to N or P alone).  Plant nutrient content data generally supported NDS findings.  Responses to nutrient additions compared to controls were large compared to a recent meta-analysis from a wide variety of ecosystem types, indicating that these systems are particularly sensitive to nutrient loading.