Impacts of ocean acidification under multiple stressors on typical organisms and ecological processes

Abstract

The oceans are taking up over one million tons of fossil CO ₂ per hour, resulting in increased pCO ₂ and declining pH, leading to ocean acidification (OA). At the same time, accumulation of CO ₂ and other greenhouse gases is causing ocean warming, which enhances stratification with thinned upper mixed layers, exposing planktonic organisms to increasing levels of daytime integrated UV radiation. Ocean warming also reduces dissolved oxygen in seawater, resulting in ocean deoxygenation. All these ocean global changes are impacting marine ecosystems and effects are well documented for each individual driver (pH, oxygen, temperature, UV). However, combined effects are still poorly understood, strongly limiting our ability to project impacts at regional or local levels. Different regions are often exposed (and often adapted) to contrastingly different physical and chemical environmental conditions and organisms, and ecosystems from different parts of the world will be exposed to unique combinations of stressors in the future. Understanding the modulating role of adaptation, species niche and stressors’ interaction is key. This review, being a non-exhaustively explored one, aims to provide an overview on understandings of ecophysiological effects of OA and its combination with covarying drivers, mainly warming, deoxygenation and solar UV radiation. We propose a testable hypothetical model as well as future research perspectives.