Different response-effect trait relationships underlie contrasting responses to two chemical stressors

1. Trait-based approaches predict ecosystem functioning under environmental change by relating traits predicting changes in species densities (response traits) to traits driving ecosystem functioning (effect traits). Stressors can however affect ecosystem functioning not only by altering species densities, but also by directly changing species effect traits. 2. We first identified the response traits predicting the cell density of 18 marine benthic diatom strains along gradients of two chemical stressors (a pesticide and a metal, atrazine and copper). We then tested if response traits could predict stressor-induced changes in ecosystem functioning, i.e. changes in the effect traits driving the diatoms’ potential contribution to primary production, sediment stabilization and energy content in intertidal systems. Finally, we examined if changes in density and changes in ecosystem functioning were correlated, to assess whether species capable of growing under stressful conditions could mai...