d13C and d15N reveal significant differences in the coastal foodwebs of the seas surrounding Trinidad and Tobago

Abstract

This study assessed nearshore, marine ecosystem function around Trinidad and Tobago (TT). The coastline of TT is highly complex, bordered by the Atlantic Ocean, the Caribbean Sea, the Gulf of Paria and the Columbus Channel, and subject to local terrestrial runoff and regional riverine inputs (e.g. the Orinoco and Amazon rivers). Coastal organisms can assimilate energy from allochthonous and autochthonous sources. We assessed whether stable isotopes δ13C and δ15N could be used to provide a rapid assessment of trophic interactions in primary consumers around the islands. Filter-feeding (bivalves and barnacles) and grazing organisms (gastropods and chitons) were collected from 40 marine sites during the wet season. The flesh of organisms was analysed for δ13C and δ15N. Results indicate significant variation in primary consumers (by feeding guild and sampling zone). This variation was linked to different energy sources being assimilated by consumers. Results suggest that offshore production is fuelling intertidal foodwebs; for example, a depleted δ13C signature in grazers from the Gulf of Paria, Columbus Channel and the Caribbean and Atlantic coastline of Tobago indicates that carbon with an offshore origin (e.g. phytoplankton and dissolved organic matter) is more important than benthic or littoral algae during the wet season. Results also confirm findings from other studies indicating that much of the coastline is subject to cultural eutrophication. This study revealed that ecosystem function is spatially variable around the coastline of TT. This has clear implications for marine resource management, as a single management approach is unlikely to be successful at a national level.