Nutrient dynamics in Indonesian seagrass beds : factors determining conservation and loss of nitrogen and phosp[h]orus

Seagrasses are marine angiosperms that occur in shallow coastal seas around the world. They have reached their highest species diversity in Southeast Asia, where they formextensive multi-species meadows. The seagrass beds in Indonesia maintain a high productivity despite a low nutrient availability. It has been hypothesised, therefore, that these seagrass beds are largely self-sustaining and that most nutrients are efficiently re-used within the system. Due to the dynamic character of coastal habitats, however, seagrass beds may be considered as open systems with regard to nutrient fluxes. Water currents may lead to the export of leaves and leaf fragments and a concomitant nutrient loss. Other processes that contribute to nutrient losses are herbivory, diffusion from the sediment, exudation and leaching from living and decomposing plant material, and, as far as nitrogen is concerned, denitrification. The long-term persistence of seagrass meadows obviously dependson the replenishment of these nutrient losses. For seagrasses of coastal habitats, ample nutrient replenishment is provided by river discharges or diffuse terrestrial run-off. For seagrass meadows on the numerous off-shore coral islands, however, nutrient replenishment is often not self-evident. So far, no data exist on the processes of nutrientlosses and gains for these seagrass systems. The studies in this thesis provide data on the conservation and loss of nitrogen and phosphorus in such meadows in the Spermonde Archipelago, South Sulawesi, Indonesi