Diversity patterns of echinoids (Echinodermata: Echinoidea) in shallow waters of the Mexican Pacific

Abstract

The Mexican Pacific hosts a large diversity of echinoids occupying different habitats and ecological niches; nevertheless, the group remains scarcely studied in terms of their spatial patterns of biodiversity and variation in the region. This work evaluated the alpha, beta, and gamma diversity of echinoids living in the Mexican Pacific's shallow waters (0–200 m) at three spatial scales: Operational geographic units (OGUs), ecoregions, and provinces. Alpha diversity was evaluated through the standardized coverage values of 0D, 1D, and 2D, while the contribution of alpha and beta diversity components to gamma diversity was estimated with additive partitioning. Finally, we evaluated whether beta diversity resulted from overlap, species replacement, or richness differences. A total of 45 species and 2,232 incidences were registered in the 150 OGUs distributed throughout the Mexican Pacific. Cluster completeness in the ecoregions of the Warm Temperate Northeast Pacific (WTNP) province was higher (> 95 %) than in the ecoregions of the Eastern Tropical Pacific (TEaP) province. Standardized coverage values of the 0D, 1D, and 2D indices showed differences between the ecoregions Cortezian and Magdalena Transition in the WTNP province. At the ecoregion and province level, alpha diversity might be influenced by sampling techniques and habitat availability, which limits the distribution of regular and irregular echinoids. Gamma diversity is mainly determined by beta diversity at the ecoregion scale, where species overlap and richness differences were the major contributing components, probably resulting from substrate dependence, habitat availability, and mesoscale ocean circulation patterns.