Richness, abundance and spatial heterogeneity of gastropods and bivalves in coral ecosystems across the Mexican Tropical Pacific

The diversity of gastropods and bivalves, total mollusc richness and total mollusc abundance were analysed for three substrates (coral, rock and sand) in the coral and reef ecosystems of the Mexican Tropical Pacific (MTP). Up to 3,828 individuals (70% gastropods and 30% bivalves), belonging to 209 species (146 gastropods and 63 bivalves), were identified; this is one of the most diverse molluscan faunas (2.77 species/m2) associated with reef systems in the MTP. Evaluation of the sampling effort demonstrated that 80% of gastropod species and 93% of bivalve species inhabiting the reef system were recovered. The highest abundance occurred in the coral substrate (1,939 individuals), while the highest species richness was found on the rock substrate (131 species). The analysis showed that the greatest spatial variation in total mollusc, gastropod and bivalve diversity occurred among different substrates within individual localities, with minor differences among assemblages with increasing spatial scale reflecting the relative homogeneity of the molluscan fauna in the study area. While the gastropods Conus nux, Steironepion piperatum and Muricopsis zeteki accounted for differences among different regions, and Vermicularia pellucida eburnea and Bostrycapulus aculeatus accounted for differences among states, the abundances of M. zeteki, B. aculeatus and V. pellucida eburnea were related to differences in diversity at the scale of individual localities. Among bivalves, Leiosolenus aristatus, L. plumula and Gastrochaena ovata accounted for differences between regions, states and localities, respectively. Overall, the study shows that species composition is influenced by both the substrate and the geographical location of assemblages. This indicates that conservation strategies should address preserving habitat heterogeneity at local scales in the study area.