Influence of habitat structure and environmental regime on spatial distribution patterns of macroinvertebrate assemblages associated with seagrass beds in a southern Gulf of Mexico coastal lagoon

Seagrass meadows are important for their ecological functions and ecosystem services, including habitat and shelter for a high diversity of species. The present study aims to assess the spatial distribution patterns of macroinvertebrate assemblages associated with Thalassia testudinum beds in a tropical coastal lagoon of the southern Gulf of Mexico. Environmental variables and core samples were taken from three shallow beds with different degrees of exposure to wind-driven waves: protected, exposed and semi-exposed. A total of 40 benthic macroinvertebrate species were recorded, molluscs being the most important group in terms of diversity and abundance. The highest species richness was recorded at the semi-exposed site (31 species), while the highest abundance was at the exposed site (5207 ind. m(-2)). Despite inter-site variations in environmental variables and physical descriptors of seagrass (seagrass biomass, shoot density, leaf length), the species richness and abundance of macroinvertebrates correlated only with seagrass biomass. Multivariate analyses showed a clear separation of macroinvertebrate assemblages into two main groups according to the degree of exposure of the sites as exposed/semi-exposed or protected. It was also determined that seagrass biomass, hydrodynamism, sedimentation/resuspension rates and the proportion of coarse particles in the sediment appear to be the variables that best explain the differences between sites. These findings support the importance of including sites with different degrees of exposure in assessing the biodiversity of seagrass beds at the landscape scale, because species composition, species richness and the abundance of associated fauna may vary considerably between sites within the same coastal region according to a combination of biotic and abiotic factors.