Patterns of primary production and nutrient availability in a Bahamas lagoon with fringing mangroves

The role of submerged autotrophs in the productivity of tropical lagoons an d the potential influence of fringing mangroves was investigated by charact erizing primary productivity and nutrient patterns in a Bahamas lagoon, Sed iment, water, and seagrass tissue nutrient content was determined at 5 site s along a transect from a fringe mangrove to tidal channel site, Productivi ty of seagrass Thalassia testudium, sandflats, and the mangrove prop-root a lgal community was measured along the transect using benthic chambers, whil e phytoplankton and epiphyte production was quantified via light-dark bottl e experiments, Sediment phosphorus and nitrogen decreased from 0.24 +/- 0.0 4 to 0.09 +/- 0.01 and 3.23 +/- 1.01 to 1.44 +/- 0.69 mg g(-1) dry wt from the mangrove to seagrass channel site. Nutrient levels in the water column and plant tissues followed a similar spatial trend. Leaf, root, and rhizome C:P molar ratios at the mangrove site (641 +/- 30, 1208 +/- 385, and 595 /- 71) were low compared to those of the lagoon (761 +/- 70, 2220 +/- 463, and 1137 +/- 289) and channel (953 +/- 42, 2177 +/- 349, and 2003 +/- 293) sites, indicating that seagrass beds adjacent to fringe mangroves have high er nutrient availability. While these nutrient trends were significant, the y did not result in higher net community primary production (NPP) in beds a djacent to the mangroves. All seagrass sites had high NPP rates (1.65 to 2. 29 g C. m(-2) d(-1)). NPP rates of epiphytes (5.22 +/- 1.44 g C. kg(-1) d(- 1)) and prop-root algae (8.54 +/- 6.41 g C kg(-1) d(-1)) approached those o f seagrass (10.49 +/- 3.76 to 13.18 +/- 5 68 g C kg(-1) d(-1)). Based on se diment, water column nutrient patterns and tissue stoichiometry, seagrasses in close proximity to the mangrove fringe had the greatest nutrient availa bility among sites. However, seagrass community NPP rates were similar acro ss the nutrient gradient from the mangroves to the central channel. The fri nge mangrove zone supported high algal production rates, contributing to to tal ecosystem primary production.