Food web structure of a subtropical coastal lagoon

The food webs of a coastal lagoon ecosystem in the southeastern Gulf of California were investigated through the use of stomach contents analyses and carbon (delta C-13) and nitrogen (delta N-15) stable isotopes of fish and macroinvertebrates. Food sources and species representative of primary producers and primary-to-tertiary consumers were examined. Macroinvertebrates (47.5%) and fish (45%) assemblages represented over 90% of the total biomass. The most representative groups were fish (45%), crustaceans (24%), mollusks (16%), and echinoderms (8.5%). Based on the results from stomach content analysis, stable isotope analysis, and mixing models using Bayesian statistics, the estuarine food web was reconstructed from food chain bases to tertiary consumers, including the most representative species in the ecosystem. Four food webs were identified according to the primary producers, and five trophic levels were identified. However, in the higher trophic levels, these food webs are indistinguishable due to the high degree of omnivory and the complexity of the system which allows the predation in different environments.