MEPS 219:109-119 (2001)  -  doi:10.3354/meps219109

ABSTRACT: The role of submerged autotrophs in the productivity of tropical lagoons and the potential influence of fringing mangroves was investigated by characterizing primary productivity and nutrient patterns in a Bahamas lagoon. Sediment, water, and seagrass tissue nutrient content was determined at 5 sites along a transect from a fringe mangrove to tidal channel site. Productivity of seagrass Thalassia testudium, sandflats, and the mangrove prop-root algal community was measured along the transect using benthic chambers, while phytoplankton and epiphyte production was quantified via light-dark bottle experiments. Sediment phosphorus and nitrogen decreased from 0.24 ± 0.04 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 higher nutrient availability. While these nutrient trends were significant, they did not result in higher net community primary production (NPP) in beds adjacent 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 of seagrass (10.49 ± 3.76 to 13.18 ± 5.68 g C kg^-1 d^-1). Based on sediment, water column nutrient patterns and tissue stoichiometry, seagrasses in close proximity to the mangrove fringe had the greatest nutrient availability among sites. However, seagrass community NPP rates were similar across the nutrient gradient from the mangroves to the central channel. The fringe mangrove zone supported high algal production rates, contributing to total ecosystem primary production.

KEY WORDS: Seagrass · Thalassia · Mangroves · Community Metabolism · Nutrients · Tropics