Benthic Macrofauna, At Class Level, In A Tropical Seagrass Meadow Exposed To Open-Sea: Relation With Environmental Variables

Background: Seagrass meadows are highly productive marine ecosystems that harbor dense and diverse benthic macrofauna communities. These, seagrass ecosystems are being drastically decimated worldwide, which, in turn, affects the density and diversity of the associated macrofauna. Goals: We investigated if the benthic macrofaunal community structure in a tropical seagrass meadow exposed to the open sea is related to the gradient of environmental and biological factors generated by the distance from the coast. Methods: The study was conducted in the seagrass meadow from Los Petenes Biosphere Reserve. Biological samples and environmental variables were obtained by triplicate at twelve sampling sites divided into three transects located at 0.5, 9.0, and 17.0 km from the coast. Results: Benthic macrofaunal density varied from 933 to 2550 indv. m-2. The collected specimens belonged to ten taxonomic classes: Asteroidea, Bivalvia, Echinoidea, Gastropoda, Holothuroidea, Malacostraca, Ophiuroidea, Polychaeta, Polyplacophora, and Sipunculidea. Taxonomic composition from far from the coast transects was homogeneous within transects but different between transects. Taxonomic composition of near to the coast transect was heterogeneous, mainly influenced by the low diversity of classes from the site closest to the Campeche city. Conclusions: In this tropical seagrass meadow, the composition of the benthic macrofauna is mainly modulated by a set of environmental variables that gradually change from the coast to the open sea: Thalassia testudinum biomass, algae biomass, depth, and phosphate levels in sediment. In contrast, the maximum density of the benthic macrofauna is limited to an optimal biomass of the dominant seagrass species T. testudinum. This relationship is not lineal, but it follows a Log-Normal distribution pattern.