Patterns in Taxonomic and Functional Diversity of Macrobenthic Invertebrates Across Seagrass Habitats: a Case Study in Atlantic Canada

Abstract

Functional diversity (FD) characterizes the role of species within communities based on their morphological, behavioural and life history traits. Taxonomic diversity is not always a surrogate for FD, and ecosystem functioning is more dependent on functional traits rather than species richness. Despite this, most diversity studies in seagrass ecosystems do not consider the functional trait landscape. Here, we compare and contrast the taxonomic and functional diversity and composition of macrobenthic invertebrates (infauna and small epifauna) across a gradient of seagrass habitats (bare sediment, bed edge and bed interior) at three sites in Nova Scotia, Canada. We also determine the relationship between taxonomic diversity and FD to gain insight into the consequences of species loss. At two sites, we found that taxonomic diversity (species number and Margalef and Simpson’s indices) increased from bare sediments to the bed interior, while FD (Rao index) did not or else showed a weaker pattern. At a third site, both taxonomic and functional diversity tended to increase across the seagrass gradient. Despite the differences in relationships between taxonomic and functional diversity, functional trait composition tended to be distinct across seagrass habitats at all sites. Regressions showed that FD increased either hyperbolically or linearly with taxonomic diversity. Our study suggests that for seagrass ecosystems similar to the ones sampled, the implications of species loss for ecosystem functioning may not be easily predicted from data of taxonomic diversity alone. This study provides some of the first data of taxonomic and functional diversity in seagrass ecosystems, which can be used to inform conservation objectives and management practices.