Are physiological and ecosystem-level tipping points caused by ocean acidification? A critical evaluation

• Published in: Earth System Dynamics
• Main Authors: C. E. Cornwall, S. Comeau, B. P. Harvey
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2024
• Subjects: Science; Q; Geology; QE1-996.5; Dynamic and structural geology; QE500-639.5; Ocean acidification
• Online Access: https://doi.org/10.5194/esd-15-671-2024; https://doaj.org/article/7011cffe29ef487189bbd86a1a706978

Ocean acidification (OA) is predicted to cause profound shifts in many marine ecosystems by impairing the ability of calcareous taxa to calcify and grow and by influencing the physiology of many others. In both calcifying and non-calcifying taxa, ocean acidification could further impair the ability of marine life to regulate internal pH and thus metabolic function and/or behaviour. Identifying tipping points at which these effects will occur for different taxa due to the direct impacts of ocean acidification on organism physiology is difficult because they have not adequately been determined for most taxa nor for ecosystems at higher levels. This is due to the presence of both resistant and sensitive species within most taxa. However, calcifying taxa such as coralline algae, corals, molluscs, and sea urchins appear to be most sensitive to ocean acidification. Conversely, non-calcareous seaweeds, seagrasses, diatoms, cephalopods, and fish tend to be more resistant or even benefit from the direct effects of ocean acidification, though the effects of ocean acidification are more subtle for these taxa. While physiological tipping points of the effects of ocean acidification either do not exist or are not well defined, their direct effects on organism physiology will have flow-on indirect effects. These indirect effects will cause ecological tipping points in the future through changes in competition, herbivory, and predation. Evidence for indirect effects and ecological change is mostly taken from benthic ecosystems in warm temperate–tropical locations in situ that have elevated CO 2 . Species abundances at these locations indicate a shift away from calcifying taxa and towards non-calcareous taxa at high-CO 2 concentrations. For example, lower abundance of corals and coralline algae and higher covers of non-calcareous macroalgae, often turfing species, are often found at elevated CO 2 . However, there are some locations where only minor changes or no detectable changes occur. Where ecological tipping points do ...