Nutrient content of the seagrass Thalassia testudinum reveals regional patterns of relative availability of nitrogen and phosphorus in the Florida Keys USA

Abstract

Between 1992 and 2000, we sampled 504 randomly chosen locations in the Florida Keys, Florida, USA, for the elemental content of green leaves of the seagrass Thalassia testudinum. Carbon content ranged from 29.4-43.3% (dry weight), nitrogen content from 0.88-3.96%, and phosphorus content from 0.048-0.243%. N and P content of the samples were not correlated, suggesting that the relative availability of N and P varied across the sampling region. Spatial pattern in C:N indicated a decrease in N availability from inshore waters to the reef tract 10 km offshore; in contrast, the pattern in C:P indicated an increase in P availability from inshore waters to the reef tract. The spatial pattern in N:P was used to define a P-limited region of seagrass beds in Florida Bay and near shore, and an N-limited region of seagrass beds offshore. The close juxtaposition of N-and P-limited regions allows the possibility that N loading from the suburban Florida Keys could influence the offshore, N-limited seagrass beds without impacting the more nearshore, P-limited seagrass beds.