Functional responses of intertidal communities to environmental stress gradientsReef-associated Biodiversity

Mathieu Cusson¹, Sonia C. Morón Lugo¹, Ricardo A. Scrosati²

¹Université du Québec à Chicoutimi, Canada - ² St. Francis Xavier University, Canada

Environmental stress plays a key role in shaping community structure and biodiversity in different ecosystems. An environmental stress model (ESM) predicts variation in species richness in local communities in response to environmental stress. While the effects of stress on taxonomic richness are well studied, its effects on functional richness remain underexplored. This study adjusts the ESM to a functional approach and investigates how community function is influenced by two major drivers of stress in intertidal habitats: elevation and wave exposure. We used data from Nova Scotia, Canada. Using functional trait data for 54 intertidal taxa, we calculated functional richness and assessed the occurrence of unique functional traits at three levels of wave exposure and elevation. We hypothesised that functional richness would decrease towards higher elevations and wave-exposed habitats due to the marked increase in physiological and physical stresses, respectively, in such environments. Our results supported these predictions, mirroring patterns previously documented for taxonomic richness. We found patterns of trait convergence and loss of functional richness under stressful conditions, and greater sensitivity of functional indices to environmental gradients compared to taxonomic indices. These results suggest that high environmental stress acts as a functional filter, and demonstrates the value of incorporating functional traits into traditional taxonomic analyses to better understand the mechanisms driving community assembly along environmental gradients. Overall, this study highlights the importance of examining functional community aspects to improve predictions based on the ESM and to better anticipate ecosystem responses to future environmental changes.