Understanding coralline algal responses to ocean acidification: Meta‐analysis and synthesis

Abstract

Ocean acidification (OA) is a major threat to the persistence of biogenic reefs throughout the world's ocean. Coralline algae are comprised of high magnesium calcite and have long been considered one of the most susceptible taxa to the negative impacts of OA. We summarize these impacts and explore the causes of variability in coralline algal responses using a review/qualitative assessment of all relevant literature, meta‐analysis, quantitative assessment of critical responses, and a discussion of physiological mechanisms and directions for future research. We find that most coralline algae experienced reduced abundance, calcification rates, recruitment rates, and declines in pH within the site of calcification in laboratory experiments simulating OA or at naturally elevated CO2 sites. There were no other consistent physiological responses of coralline algae to simulated OA (e.g., photo‐physiology, mineralogy, and survival). Calcification/growth was the most frequently measured parameters in coralline algal OA research, and our meta‐analyses revealed greater declines in seawater pH were associated with significant decreases in calcification in adults and similar but nonsignificant trends for juveniles. Adults from the family Mesophyllumaceae also tended to be more robust to OA, though there was insufficient data to test similar trends for juveniles. OA was the dominant driver in the majority of laboratory experiments where other local or global drivers were assessed. The interaction between OA and any other single driver was often additive, though factors that changed pH at the surface of coralline algae (light, water motion, epiphytes) acted antagonistically or synergistically with OA more than any other drivers. With advances in experimental design and methodological techniques, we now understand that the physiology of coralline algal calcification largely dictates their responses to OA. However, significant challenges still remain, including improving the geographic and life‐history spread of research effort and a need for holistic assessments of physiology.

Coralline Algae at the Paleocene/Eocene Thermal Maximum in the Southern Pyrenees (N Spain)

“…Coralline algae, fully calcified marine autotrophic organisms, are one of the most endangered algal groups due to global temperature increase and ocean acidification (e.g., Martin and Hall-Spencer, 2017;Cornwall et al, 2021). Laboratory studies and field observations indicate that coralline algae might be negatively affected due to ocean acidification derived from the greenhouse gasses release (Anthony et al, 2008;Hall-Spencer et al, 2008;Martin and Gattuso, 2009;Büdenbender et al, 2011;Diaz-Pulido et al, 2012;Kamenos et al, 2013;Guy-Haim et al, 2016;Martin and Hall-Spencer, 2017;Peña et al, 2020a;Cornwall et al, 2021).…”

“…Coralline algae, fully calcified marine autotrophic organisms, are one of the most endangered algal groups due to global temperature increase and ocean acidification (e.g., Martin and Hall-Spencer, 2017;Cornwall et al, 2021). Laboratory studies and field observations indicate that coralline algae might be negatively affected due to ocean acidification derived from the greenhouse gasses release (Anthony et al, 2008;Hall-Spencer et al, 2008;Martin and Gattuso, 2009;Büdenbender et al, 2011;Diaz-Pulido et al, 2012;Kamenos et al, 2013;Guy-Haim et al, 2016;Martin and Hall-Spencer, 2017;Peña et al, 2020a;Cornwall et al, 2021). Nonetheless, contradictory or non-conclusive results have also been obtained (Martin and Hall-Spencer, 2017;Peña et al, 2020a;Cornwall et al, 2021;and references therein) due to acclimation of coralline algae to acidification, physiological advantages (preadaptations) or interaction with other non-calcified epiphytes growing on corallines (Martin and Hall-Spencer, 2017;Guy-Haim et al, 2020;Peña et al, 2020a;Cornwall et al, 2021).…”

Stylasterid corals build aragonite skeletons in undersaturated water despite low pH at the site of calcification

“…As the Mg content of calcite increases further (> 140 mmol/mol Mg/Ca) the solubility of this high-Mg calcite falls below even that of aragonite. Organisms that adopt this more soluble mineral form to build their skeletons include crustose coralline algae 12 .…”

Consequences of warming and acidification for the temperate articulated coralline alga, Calliarthron tuberculosum (Florideophyceae, Rhodophyta)

“…2010, Cornwall et al. 2021), whereas the impacts of warming can be negative or positive depending on species‐specific thermal tolerances. While OA and warming often occur simultaneously in marine ecosystems, fewer studies have tested these multi‐stressor impacts in a fully factorial design.…”

“…Responses of coralline algae to global climate change have largely been reported as negative (Hofmann and Bischof 2014, McCoy and Kamenos 2015, Cornwall et al. 2021) and most studies have focused on OA as the primary stressor (Cornwall 2019). Negative responses of coralline algae to OA include reduced recruitment (Kuffner et al.…”