Ecological and functional diversity of gastropods associated with hermatypic corals of the Mexican tropical Pacific

Abstract

This study used multi-scale models to evaluate spatial variation in the structure of the assemblage and functional groups of gastropods associated with hermatypic corals of the Mexican Tropical Pacific. A geographic model examined the spatial scales of the region, geographic position and sites, while an oceanographic model considered the oceanographic characteristics and sites. The relationship between gastropods and environmental and spatial variables was analyzed with additive partitions, based on canonical correspondence analysis. Both models coincide in that the greatest variation of gastropods was presented at quadrant (i.e., small-scale) and site (i.e., local-scale) levels, and the lowest variation to the scale of geographic position and oceanographic characteristics (i.e., medium-scale). Abundance and Shannon diversity presented greater variation at small and local-scales, while species richness presented greater variation at medium-scale. The functional groups varied to the greatest extent at medium-scale in the geographic model and at local-scale in the oceanographic model. The highest abundance, richness and diversity were found at: (1) Plataforma Pavonas and Tunel Amarradero, ~20°N (Northern region), influenced by the California Current and the Mexican Coastal Current; (2) Caleta de Chon and Morro Potosi, ~17°N (Southern region), affected by the Mexican Warm Pool; and (3) Salchi and Isla Montosa, where relatively high biological productivity occur mainly due to coastal upwelling, ~15°N (Southern region). The carnivorous epifauna was the most important functional group at all studied scales. The most important species in both models were the corallivore Coralliophila monodonta, the symbiont Muricopsis zeteki, Triphora hannai of sandy substrate and Vermicularia pellucida eburnea and Engina tabogaensis of hard substrate. Variation among sites was explained mainly by the coverage of sessile taxa (e.g., percentage of coverage of the coral Pocillopora spp., bryozoans, hydrozoans, octocorals and sponges) and proportion of substrates (e.g., sand, rock, dead coral and rubble). However, at upwelling sites, other variables such as primary productivity and phosphate concentration also contributed to local-scale variation. At medium-scale, oceanographic characteristics explain the variation of the assemblage and functional groups of gastropods.