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
dominate animals at 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 Modeling of Species Communities, a
trait-based joint species distribution model, to analyze 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 which
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 favoring 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.