Additive impacts of ocean acidification and ambient ultraviolet radiation threaten calcifying marine primary producers

Ocean acidification (OA) represents a threat tomarine organisms and ecosystems. However, OA rarely exists in isolation but occurs concomitantly with other stressors such as ultraviolet radiation (UVR), whose effects have been neglected in oceanographical observations. Here, we perform a quantitative meta-analysis based on 373 published experimental assessments from 26 studies to examine the combined effects of OA and UVR onmarine primary producers. The results reveal predominantly additive stressor interactions (69-84% depending on the UV waveband), with synergistic and antagonistic interactions being rare but significantly different between micro- and macroalgae. In microalgae, variations in interaction type frequencies are related to cell volume, with antagonistic interactions accounting for a higher proportion in larger sized species. Despite additive interactions being most frequent, the small proportion of antagonistic interactions appears to have a stronger power, leading to neutral effects of OA in combinationwith UVR. High levels of UVR at near in situ conditions in combinationwith OA showed additive inhibition of calcification, but not when UVR was low. The results also reveal that the magnitude of responses is strongly dependent on experimental duration, with the negative effects of OA on calcification and pigmentation being buffered and amplified by increasing durations, respectively. Tropical primary producers were more vulnerable to OA or UVR alone compared to conspecifics from other climatic regions. Our analysis highlights that further multi-stressor long-term adaptation experiments with marine organisms of different cell volumes (especially microalgae) from different climatic regions are needed to fully disclose future impacts of OA and UVR. (c) 2021 Elsevier B.V. All rights reserved.

Automated summary

The study found that ocean acidification and ultraviolet radiation mainly exhibit additive stressor interactions on marine primary producers. Different sizes of algae show variations in interaction type frequencies, while the effects of high UVR on OA are amplified or mitigated depending on the duration.