Ecological characteristics of the Rio Cupeyes

Background/Question/Methods   The Rio Cupeyes is a tropical stream selected to be the STREON site for Atlantic Neotropical Domain of NEON. It is a tributary of the Guanajibo River in the western part of Puerto Rico, with a catchment area of 11.3 km2. There is currently little human activity in the watershed, though there is evidence of past agricultural use. The upper reaches of the watershed are protected in a state forest and the watershed spans a gradient from wet forest to a transition between moist and dry forest. Bedrock in the watershed is mostly serpentine, with some limestone outcrops. We have been monitoring the Rio Cupeyes for nearly two years to characterize and understand the ecology of the stream and how it compares to previously studied streams in the Luquillo LTER. We have monitored nutrient levels and shrimp abundance in the stream, and species composition, litterfall and decomposition in the riparian forest. Litterfall of leaves, sticks, and fruits and flowers was monitored for 12 months along the stream.

Results/Conclusions   Stream nutrients are low compared with other streams in wet and moist forest on the island. Mg was higher in the Cupeyes than in other PR streams, as expected from serpentine areas, but calcium was not as low as expected. The riparian forest was dominated by Mangifera indica, Syzygium jambos and Calophyllum brasiliense. Some components of the ecosystem responded to seasonality. Peak litterfall occurred in February, which corresponds to the dry season. Initial litter decomposition was fast, but after two months the rate of decomposition decreased. Based on other studies in neotropical forests, the decrease in decomposition rate is likely due to a decrease in precipitation. Higher shrimp abundance appears to correspond to the wet season, with females being gravid during the fall. Understanding litterfall dynamics and leaf decomposition is important for understanding nutrient fluxes and habitat quality for stream systems and their biota.