Ecological indicators based on fish biomass distribution along trophic levels: an application to the Terminos coastal lagoon, Mexico

Abstract

Abstract Cumulative relative biomass trophic level spectra (BTLS) are constructed for the fish community of a tropical coastal lagoon in Mexico to analyse spatio-temporal patterns as a potential ecosystem indicator of multifactor impacts. Data were based on monthly trawl surveys over a single year carried out eighteen years apart. The spectra show significant differences between the two periods, indicating major shifts in the trophic structure of the system. Specifically, biomass of the omnivorous, estuarine species in the middle of the foodweb (originally dominating) has been replaced by carnivorous and herbivorous–detritivorous species. As a consequence, the initial sigmoid shape of the BTLS has tended to become more linear. However, interpretation of the causes involved remains unclear. It is suggested that this potential indicator of trophic status of the fish community reflects a combination of interacting driving forces acting simultaneously in the lagoon: (i) increased marine conditions as well as artificial reefs constructed in adjacent zones may enhance biomass of marine predators and detritivorous species; (ii) attenuation of estuarine influences may lead to decreasing biomass of estuarine generalist species; and (iii) the establishment of a marine protected area may increase predator biomass, causing a decline in prey biomass.