Université du Québec à Chicoutimi
Ph.D. candidate
Supervisor: Mathieu Cusson
Christian Nozais
Mads Thomsen, Canterbury University
Start: 2025-01-06

Project

Study of facilitation interaction within benthic intertidal communities
Biotic interactions within living communities have always been important for understanding the ecology of ecosystems. While past studies have focused primarily on competition and predation, there is now a growing focus on positive interactions. Furthermore, the role of facilitation (positive interactions of mutualism and commensalism) of foundation species is important and increasingly well understood. In mid-tidal habitats, these species are sometimes observed together, which can form facilitative cascades, where several species form a chain of positive effects on each other. These interactions remain unexplored in subarctic environments. This doctoral project aims to better understand the role of facilitative cascades within the intertidal communities of the marine St. Lawrence. Specifically, I) we will characterize the importance of facilitative cascades within intertidal communities, II) we will verify the mechanisms involved, and III) we will measure whether their properties are maintained along environmental gradients. To meet these objectives, we will explore in situ the interactions between founding species (eelgrass, macroalgae and mussels) by comparing the species alone and in combination and measure their effects on the components of taxonomic diversity (identity, abundance, richness) and functional traits of associated organisms. The mechanisms involved in facilitative cascades will be elucidated by conducting a series of field experiments, manipulating the founding species in assemblages and measuring the associated species that will establish there. In particular, the dimensions of the effects of abundance (by playing on their biomass/number), complexity (with homogeneous/simple and heterogeneous/complex structures) and functionality (with living or non-living tissues) will be explored. We will also manipulate in the field assemblages of founding species along environmental gradients (height in the foreshore; exposure to waves). The importance of cascades will be established by measuring the number and strength of interaction in various habitats subject to different environmental stresses. This project seeks to advance fundamental knowledge on intertidal communities and the interactions that structure them. This key knowledge could be reused to establish actions to preserve biodiversity in a context where the latter is increasingly threatened.