Functional changes across marine habitats due to ocean acidification

Global environmental change drives diversity loss and shifts in community structure. A key challenge is to better understand the impacts on ecosystem function and to connect species and trait diversity of assemblages with ecosystem properties that are in turn linked to ecosystem functioning. Here we quantify shifts in species composition and trait diversity associated with ocean acidification (OA) by using field measurements at marine CO2 vent systems spanning four reef habitats across different depths in a temperate coastal ecosystem. We find that both species and trait diversity decreased, and that ecosystem properties (understood as the interplay between species, traits, and ecosystem function) shifted with acidification. Furthermore, shifts in trait categories such as autotrophs, filter feeders, herbivores, and habitat‐forming species were habitat‐specific, indicating that OA may produce divergent responses across habitats and depths. Combined, these findings reveal the importance of connecting species and trait diversity of marine benthic habitats with key ecosystem properties to anticipate the impacts of global environmental change. Our results also generate new insights on the predicted general and habitat‐specific ecological consequences of OA. Among the many escalating threats to Earth's ecosystems, ocean acidification is expected to profoundly alter the diversity and functioning of marine ecosystems. This study highlights the importance of understanding the link between species, traits, and ecosystem properties that are in turn linked to ecosystem functioning. Through benthic field surveys at marine CO2 vent systems spanning four reef habitats across different depths, and trait‐based approaches, this study reveals loss in trait diversity and shifts in ecosystem properties with acidification on temperate rocky reefs.