Spatial analysis of bivalve mollusks diversity in Mazatlan Bay, Mexico

Mazatlan Bay is considered the northern boundary of the region with the greatest species richness of infaunal and epifaunal bivalve mollusks in the tropical eastern Pacific. The present study aimed to quantify changes in the patterns of bivalve species diversity in Mazatlan Bay at different spatial scales and to determine which scale contributes more towards the species turnover of the total diversity in the Bay. Additive and multiplicative partitions were performed in the α, β and γ diversities of four sites and two environments (intertidal and shallow subtidal) within the Bay. A total of 19,848 individuals from 27 families and 77 species of bivalves were recorded. The effectiveness of the sampling effort was evaluated using species accumulation curves, which revealed a representation of 73% in the four sites and two environments. Rarity was characterized by 20% of the singleton and unique species, and 9% of the doubletons and duplicate species. Additive partitioning showed that the species turnover among sites and between environments contributed more to bivalve total diversity. In multiplicative partitions of the sites in both environments, the greatest species richness was found at the lower scales (α1). The sites and environments showed a clear decrease in the abundant (N1) and very abundant species (N2) from α to β1–β2 scales. The spatial variability of the different habitats of the bay is important to maintain the high species richness and high percentage of different life forms found in the Bay. The β1 and β2-diversities constitute the most important component for supporting the bivalve total diversity (γ) of Mazatlan Bay.