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 δ¹³C values of carbon sources varied from − 30.6 to − 26.9‰. Consumers were separated into invertebrates (with δ¹³C mean values from − 24.8 ± 0.3‰ to − 15.7 ± 0.7‰) and fish (with δ¹³C mean values from − 21.2 ± 1.3‰ to − 17.2 ± 0.9‰). Benthic mobile invertebrates generally had depleted δ¹³C values related to different trophic pathways to those of filter feeders and fish (with more enriched δ¹³C values). In agreement with similar studies in estuarine macro-tidal areas (e.g., Brazil and Panamanian Pacific), the large range in δ¹³C 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, δ¹⁵N values correctly reflected the trophic levels, as species from lower trophic levels had lower δ¹⁵N than species from higher trophic levels. The trophic length of the food web was estimated from producers to higher consumers based on δ¹⁵N values. Taking into account a nitrogen trophic fractionation value of 3.4‰, the studied system exhibited a food web with four trophic levels. Based on the distribution of consumer trophic guilds in the δ¹³C-δ¹⁵N plane and the mixing model results, we recognized that at least two main pathways are present in the system to support the community.