In light of predicted global change scenarios and biodiversity loss, it is increasingly important to understand how biodiversity-ecosystem functioning relationships vary under increasingly disturbed conditions. In particular, it is critical that we better understand the impacts of multiple stressors on the role of biodiversity across a range of trophic levels. Predicted increases in eutrophication events and sedimentation, alongside climate-driven range shifts of key consumer species, are likely to have substantial effects on coastal communities. We examined experimentally the top-down effects of trophic complexity on the structure and stability of natural marine benthic communities exposed experimentally to nutrient enrichment and elevated sedimentation over 15 months.
We found that effects of multiple stressors on community stability were moderated by trophic complexity. In particular, elevated sedimentation increased algal spatial variability, but this effect varied between plots of different trophic complexity and with addition of nutrients. Nutrient enrichment increased algal temporal variability, but this effect varied with trophic complexity. Regardless of perturbations, reductions of trophic complexity led to distinct shifts in the structure and stability of algal assemblages. Our findings suggest that the nature of stressor interactions vary with changes in trophic complexity and among response variables, leading to less predictable consequences for the structure, functioning and stability of communities. This highlights the need to measure multiple components of ecological stability to avoid underestimating potential impacts of perturbations.