A Two-Decade Overview of the Ecological Carrying Capacity in Bahía Santa Maria-La Reforma Coastal Lagoon System

Santa María Bay-La Reforma (SMBLR) is Mexico's most extensive estuarine lagoon system. The Secretariat of the Ramsar Convention on Wetlands declared it a wetland of international importance and it is made up of islands, estuaries, and mangrove areas, which provide a vital part of the habitat and refuge of a significant number of birds, fish, amphibians, reptiles, and mammals. The fishing of blue and brown shrimp, marine and estuarine fish, as well as the exploitation of crab and bivalve mollusks represent an important economic value for the established communities that live there and for the economic impact in the state of Sinaloa. This state ranked second in fisheries production and first in aquaculture production by 2023. Also, Mexico is the seventh largest producer of farmed crustaceans in the world. However, the biological richness of this ecosystem has historically been threatened by economic activities that, via watersheds, translate into continuous inputs of nutrients and other pollutants. This has led to modifications to the system such as changes in the structure of pelagic and benthic communities, mainly in response to the phenomenon of eutrophication. To understand the dynamics of nutrient inputs to the ecosystem, this work presents a comparative analysis of the trophic state of the system and the magnitude of the main economic activities which have been modified from dominance of livestock activities to aquaculture from 2007-2019. In the coastal component of SMBLR (agriculture, livestock and aquaculture) under hydrological criteria, the behavior of the system's trophic indices in each season of the year and its transitions were analyzed. We found, however, that in most of the seasons the system functions as a nitrogen and phosphorus sink, which is associated with autotrophic net ecosystem metabolism and nitrogen fixation processes. We suggest that while water residence times in SMBLR are short, these are strongly influenced by the high volumes of water and nutrient loads determined by the spatio-temporal variations of hydrological drainage from the drains of the basins of influence of the system. The influx of nutrients and other pollutants into an ecosystem affects the carrying capacity of the lagoon ecosystem. This is demonstrated in this study since SMBLR is mostly an autotrophic system; there are signs that the carrying capacity at some seasons of the year has been exceeded, and the adverse ecological and socioeconomic effects in the basin are evident.