A Trophic Model for a Periodically Closed Coastal Lagoon System in the Southern Mexican Pacific

Abstract

Carretas-Pereyra is an estuarine lagoon system located in the southern Mexican Pacific coast. Its connection to the sea is intermittent, because the mouth of the system closes seasonally under natural conditions, but it is often opened artificially for artisanal fishery purposes. In order to know the degree of development, structure, and functioning of this system, under intermittent communication with the sea, a trophic model was built using software Ecopath. The model was composed of 32 functional groups: one for birds, one for crocodylians, 18 for fishes, 9 invertebrates, 2 plankton, and detritus. The pedigree index of the model was 0.62, which mean it is an acceptable model. The results are consistent with findings for lagoon systems with permanent connection to the sea. Some of the ecosystemic mechanisms probably used to face the abrupt changes induced by the opening of a sea inlet are: system omnivory, elevated overhead, efficient metabolism in phytoplankton, species replacement, and species adaptability to dominant environmental conditions. These elements provide stability to the ecosystem and help in its recovery. Detritus, zooplankton, and phytoplankton were important components for the resiliency of the system. In spite of the biological and environmental changes induced by the intermittent opening of an inlet, Carretas-Pereyra has the necessary elements to absorb the impacts and function adequately.