Functional and taxonomic (α and β) diversity patterns of macrobenthic communities along a depth gradient (19–2639 m): A case study from the southern Indian continental margin

Abstract

Identifying the drivers that shape the biodiversity of a region is important to predict the response of ecosystems to environmental changes. Macrofaunal distribution pattern in the North Indian Ocean has so far been mainly studied considering small geographical areas, and using taxonomic diversity. The present study is a functional trait based approach aimed to identify the environmental drivers of macrofaunal distribution and diversity pattern from the relatively unexplored southern Indian continental margin. A total of 53 stations were sampled along six transects from a depth range of 19–2639 m. Along with taxonomic diversity (α and β), functional structure was assessed by using Biological Trait Analysis (BTA) and multivariate functional indices (richness, evenness, dispersal, divergence and Rao's Entropy). Principal Component Analysis identified a clear depth-related variability in the measured environmental parameters. Alpha diversity of the macrofaunal community decreased with increasing depth, a trend driven by depth related changes in the environmental factors (dissolved oxygen, sediment organic carbon and texture). However, functional diversity was only partially explained by the studied environmental variables which may be due to different factors governing the taxonomic and functional diversity pattern of macrofauna. Among the functional indices, only functional richness and evenness showed a clear trend of increase from shallow to deeper depths indicating that biodiversity-environment relations are complex. Therefore, investigating the response of macrofaunal community using multiple measure of diversity (α, β- and, functional diversity) was useful for providing an understanding of macrofaunal diversity pattern. The results of our study contribute to the growing knowledge on large-scale diversity gradients for marine macroinvertebrates, which may be critical for understanding ecological patterns and its response to both habitat and climatic change.