Food Web Structure and Trophic Relations in a Riverine Mangrove System of the Tropical Eastern Pacific, Central Coast of Colombia

The isotopic composition of carbon and nitrogen of sources and consumers and the mixing model stable isotope analysis in R (SIAR) were used to understand the trophic structure to identify the main carbon sources in the food web of a highly humid riverine mangrove system on the Pacific coast of Colombia. The delta C-13 values of carbon sources varied from - 30.6 to - 26.9aEuro degrees. Consumers were separated into invertebrates (with delta C-13 mean values from - 24.8 +/- 0.3aEuro degrees to - 15.7 +/- 0.7aEuro degrees) and fish (with delta C-13 mean values from - 21.2 +/- 1.3aEuro degrees to - 17.2 +/- 0.9aEuro degrees). Benthic mobile invertebrates generally had depleted delta C-13 values related to different trophic pathways to those of filter feeders and fish (with more enriched delta C-13 values). In agreement with similar studies in estuarine macro-tidal areas (e.g., Brazil and Panamanian Pacific), the large range in delta C-13 values for consumers may indicate that different carbon sources are important for the analyzed food web. In general, fish exhibited greater nitrogen values than invertebrates, indicating higher trophic levels. Among all consumers, with some exceptions, delta N-15 values correctly reflected the trophic levels, as species from lower trophic levels had lower delta N-15 than species from higher trophic levels. The trophic length of the food web was estimated from producers to higher consumers based on delta N-15 values. Taking into account a nitrogen trophic fractionation value of 3.4aEuro degrees, the studied system exhibited a food web with four trophic levels. Based on the distribution of consumer trophic guilds in the delta C-13-delta N-15 plane and the mixing model results, we recognized that at least two main pathways are present in the system to support the community.