Crustacean diversity in the Puget Sound: reconciling species, phylogenetic, and functional diversity

Biodiversity has critical phylogenetic and functional components, yet many prior studies of marine communities focus only on taxonomic diversity. Here, we surveyed intertidal crustacean communities across 11 sites in the Puget Sound (Washington state). We calculated taxonomic diversity (Shannon’s H), functional diversity (functional evenness and Rao’s Q), and phylogenetic diversity to examine how these indices were related and how they varied with environmental factors. A model selection approach (AIC) was used to examine which factors (habitat complexity, algal richness, salinity, and urbanization) were the best predictors for each index. Across sites, all four diversity indices were moderately correlated. Algal richness emerged as an important factor, occurring in well-supported models across all diversity indices: sites with more algal species had higher levels of taxonomic, functional, and phylogenetic diversity. Species diversity of both herbivores and non-herbivores was positively correlated with algal species richness, suggesting algae may be important for habitat as well as a food source. More species-rich algal communities had more phylogenetically diverse assemblages of herbivores, but algal richness was not correlated to non-herbivore phylogenetic diversity. Boulder size, but not other measures of habitat complexity, was positively correlated with functional diversity; most diversity in our samples was associated with boulders. Sites adjacent to higher levels of impervious surfaces (e.g., urbanization) had lower values of functional evenness. A growing number of studies have demonstrated that anthropogenic factors can have particularly strong effects on functional or phylogenetic diversity, and our study provides a number of tools for future investigations of crustacean diversity in this region.