Meta-analysis reveals complex marine biological responses to the interactive effects of ocean acidification and warming

Abstract

Ocean acidification and warming are considered two of the greatest threats to marine biodiversity, yet the combined effect of these stressors on marine organisms remains largely unclear. Using a meta-analytical approach, we assessed the biological responses of marine organisms to the effects of ocean acidification and warming in isolation and combination. As expected biological responses varied across taxonomic groups, life-history stages, and trophic levels, but importantly, combining stressors generally exhibited a stronger biological (either positive or negative) effect. Using a subset of orthogonal studies, we show that four of five of the biological responses measured (calcification, photosynthesis, reproduction, and survival, but not growth) interacted synergistically when warming and acidification were combined. The observed synergisms between interacting stressors suggest that care must be made in making inferences from single-stressor studies. Our findings clearly have implications for the development of adaptive management strategies particularly given that the frequency of stressors interacting in marine systems will be likely to intensify in the future. There is now an urgent need to move toward more robust, holistic, and ecologically realistic climate change experiments that incorporate interactions. Without them accurate predictions about the likely deleterious impacts to marine biodiversity and ecosystem functioning over the next century will not be possible.

Keywords: Climate change; meta-analysis; multiple stressors; ocean acidification; ocean warming; synergistic interactions.

Figure 1

The mean effect of ocean acidification (clear circles), ocean warming (gray circles), and combined ocean acidification and warming (black circles) on calcification, growth, photosynthesis, reproduction, and survival for different taxonomic groups. The mean log response ratio and ±95% confidence intervals are shown for overall (combined results), calcifiers (calcifying algae, corals, crustaceans, echinoderms, molluscs, and phytoplankton) and noncalcifiers (fishes, noncalcified algae, seagrass). The number of observations in each analysis is shown in parentheses. The zero line indicates no effect, and significance (*) of mean effects is determined when the ±95% confidence interval does not overlap zero.

Figure 2

The mean effect of ocean acidification (clear circles), ocean warming (gray circles), and combined ocean acidification and warming (black circles) on growth, photosynthesis, and survival for calcifying and noncalcifying organisms. The mean log response ratio and ±95% confidence intervals are shown for calcifiers and noncalcifiers. The number of observations in each analysis is shown in parentheses. The zero line indicates no effect, and significance (*) of mean effects is determined when the ±95% confidence interval does not overlap zero.

Figure 3

The mean effect of ocean acidification (clear circles), ocean warming (gray circles), and combined ocean acidification and warming (black circles) on calcification, growth, and survival in different life-history stages. The mean log response ratio and ±95% confidence intervals are shown for embryos, larvae, juveniles, and adults. The number of observations in each analysis is shown in parentheses. The zero line indicates no effect, and significance (*) of mean effects is determined when the ±95% confidence interval does not overlap zero.

Figure 4

The mean effect of ocean acidification (clear circles), ocean warming (gray circles), and combined ocean acidification and warming (black circles) on calcification, growth, photosynthesis, reproduction, and survival for different levels of trophic organization. The mean log response ratio and ±95% confidence intervals are shown for autotrophs and heterotrophs. The number of observations in each analysis is shown in parentheses. The zero line indicates no effect, and significance (*) of mean effects is determined when the ±95% confidence interval does not overlap zero.