Ecological responses to ocean acidification and warming: scaling up from individuals to communities

Abstract

Impacts of human CO2 emissions on ecosystems and their services are inherently difficult to predict, as ecosystem responses emerge from complex and dynamic networks of organisms and their interactions. Yet, our understanding of the ecological imprint of future climate remains largely based on tests of single species in the laboratory. Here I show how the responses of individual organisms to ocean acidification and ocean warming scale-up to species communities and reveal the underlying ecological dynamics. This was accomplished through the study of behaviour, bottom-up and top-down forcing, food web architecture, and functional composition in 1,800 L mesocosms that harboured a temperate near-shore community including various species of algae, invertebrates and fishes. The negative effects of ocean acidification were buffered effectively through stabilizing processes at both simple and complex levels of biological organisation. Consequently, acidification primarily acted as a resource (via CO2-enrichment) that increased productivity throughout the food web. In contrast, ocean warming shifted the balance in key ecological processes leading to a novel community structure that would likely undermine ecosystem services. Dynamics with the potential to compensate for the uneven sensitivities between functions failed to engage – given the fundamental influence of temperature on physiology – which allowed impacts to cascade through the community. This stress through warming also negated any positive effects of acidification. My findings bridge the gap between the simplicity of the laboratory and species communities in nature, by revealing how impacts of future climate can be countered or accelerated through ecological processes. A predictive understanding of stability or change in ecosystems is key to the management of natural resources in a future ocean.