Lagoon scale processes in a coastally influenced Caribbean system: Implications for the seagrass Thalassia testudinum

The Bocas del Toro archipelago in the Caribbean sea on the northwest coast of Panama has high annual rainfall (> 3000 mm) and a mountainous watershed, resulting in high inflow of fresh water. The two main lagoons have different geologic structure and different inputs; while Bahia Almirante has carbonate sediment and a relatively small watershed, Laguna de Chiriqui has predominantly siliclastic sediment and a very large watershed. The region also has a long history of clearing and agriculture. The purpose of this research was to use the seagrass Thalassia testudinum as a bio-indicator of nutrient status of these lagoons, particularly to assess the extent and influence of mainland inputs of freshwater, nutrients and sediments. Leaf tissue nitrogen and phosphorus, as well as surface water quality and porewater nutrients, were measured from 32 sites throughout the archipelago. The Bocas del Toro archipelago showed clear but relatively small differences in these parameters between the carbonate, moderate freshwater input Bahia Almirante and the siliclastic, high freshwater input Laguna de Chiriqui. No evidence of a mainland to offshore (Cayos Zapatillos) gradient in nutrient status was observed in T. testudinum meadows. Leaf tissue nitrogen (ca. 2.4%) and phosphorus (ca. 0.25%) as well as chlorophyll a concentrations were high throughout the archipelago and higher than many tropical seagrass dominated ecosystems of the Caribbean. It is likely that this is partly a result of the mountainous, volcanic watershed and high rainfall, but the influence of extensive agriculture and land clearing has yet to be explicitly determined. Florida Int Univ, SE Environm Res Ctr, Miami, FL 33199 USA.

Keywords: nitrogen, phosphorus, sediment, nutrient processes, Bocas del Toro, Panama PATTERNS, NITROGEN