Traits mediate environmental responses of benthic ciliates in dynamic coastal habitats

Aim

Understanding how species' traits mediate environmental responses provides a mechanistic perspective on community assembly processes. Although traits that influence the response of multicellular organisms to environments have been studied, the identification of such traits in unicellular organisms, like ciliates, is underexplored. Since ciliates are dominant animals in coastal sandy sediments and contribute significantly to interstitial community respiration, identifying links between their occurrence and sandy-coast characteristics is crucial for conserving biodiversity and protecting coastal habitats.

Location

Coasts of China.

Methods

We used Hierarchical Modelling of Species Communities, a trait-based joint species distribution model, to analyse ciliate community data collected from 344 sites belonging to 31 beaches across the Chinese coastline.

Results

We found that physical variables play the most important role in determining ciliate occurrence. The beach index combines the tidal range, sediment grain size and beach slope of beach-selected species based on body size as well as feeding type, while sediment grain size constrained different mobility types, with swimming species favouring fine sandy sediments. The significant contribution of phylogeny in explaining the residual variation among species responses indicates that there are phylogenetically conserved but unmeasured traits too that influence species' responses. Species richness of benthic ciliates was higher in dissipative beaches with high primary productivity.

Main Conclusions

Based on our research, ciliate occurrence in coastal beaches is mediated by their traits which are filtered by local environmental variables. The beach index is essential in predicting distribution patterns and species richness of benthic ciliates. Nevertheless, further research is needed to identify additional traits that will enhance the accuracy of predicting ciliate niches. Our study provides insights into the mechanisms driving ciliate community assembly processes and has implications for the conservation of biodiversity in sandy coastal habitats.