The indirect effects of ocean acidification on corals and coral communities

Abstract

Ocean acidification (OA) is a major threat to marine calcifying organisms. This manuscript gives an overview of the physiological effects of acidification on reef-building corals from a cellular to population scale. In addition, we present the first review of the indirect effects resulting from altered species interactions. We find that the direct effects of acidification are more consistently negative at larger spatial scales, suggesting an accumulation of sub-lethal physiological effects can result in notable changes at a population and an ecosystem level. We identify that the indirect effects of acidification also have the potential to contribute to declines in coral cover under future acidified conditions. Of particular concern for reef persistence are declines in the abundance of crustose coralline algae which can result in loss of stable substrate and settlement cues for corals, potentially compounding the direct negative effects on coral recruitment rates. In addition, an increase in the abundance of bioeroders and bioerosive capacity may compound declines in calcification and result in a shift towards net dissolution. There are significant knowledge gaps around many indirect effects, including changes in herbivory and associated coral–macroalgal interactions, and changes in habitat provision of corals to fish, invertebrates and plankton, and the impact of changes to these interactions for both individual corals and reef biodiversity as structural complexity declines. This research highlights the potential of indirect effects to contribute to alterations in reef ecosystem functions and processes. Such knowledge will be critical for scaling-up the impacts of OA from individual corals to reef ecosystems and for understanding the effects of OA on reef-dependent human societies.

Systematic review of the uncertainty of coral reef futures under climate change

“…Coral reef research has allocated significant effort to projecting and understanding the combined impacts of climate change and ocean acidification on coral reefs (Supplementary Data 1 & Supplementary Table 2 ). On the other hand, our analysis revealed that 16 studies in the database considered pollution to some extent, and four studies considered fishing pressure in their projections (Supplementary Data 1 & Supplementary Table 2 ) Although ocean acidification will undoubtedly have discernable effects on coral reefs 175 , there are no practical solutions available to mitigate ocean acidification, apart from the urgent reduction of greenhouse gas emissions 176 , 177 . In contrast, elevated nutrients and fishing pressure are now well recognized to increase the susceptibility of coral reefs to heatwaves 172 , 178 , 179 , and measures to address these pressures are effective and practical 180 , 181 .…”

Decline of a distinct coral reef holobiont community under ocean acidification

“…Such indirect cascading effects can impact entire trophic networks [ 22 ], including macrobe-microbe trophic interactions [ 23 ]. However, our understanding of the indirect effects of ocean acidification on coral reefs remains limited [ 24 ].…”

Reef‐wide and long‐term skeletal growth records of the mountainous star coral (Orbicella faveolata) from Belize barrier and atoll reefs (Central America)

“…Early work comparing biodiversity patterns in tropical rainforests and coral reef ecosystems (Bates, 1960; Connell, 1978) has likened coral reefs to the ‘rainforests of the sea’ based on their enormous marine biodiversity. Since the Industrial Era, coral diversity, live coral cover and recruitment have been threatened on local and global scales by a variety of environmental factors, including anthropogenically induced climate change (thermal stress due to increasing sea surface temperatures (SSTs)), ocean acidification (decreasing aragonite saturation state), mass coral bleaching and mortality events by loss of endosymbiotic zooxanthellae as a result of higher SSTs, eustatic sea‐level rise, pollution and eutrophication, hydrodynamic disturbances by tropical cyclones, diseases and macroalgal growth reducing live coral cover (Smith and Buddemeier, 1992; Bruno et al, 2003; Madin and Connolly, 2006; Baker et al, 2008; De'ath et al, 2009; Hoey et al, 2011; Vega Thurber et al, 2014; Cheal et al, 2017; Hughes et al, 2017; Mollica et al, 2018; Conti‐Jerpe et al, 2020; Guo et al, 2020; Hill and Hoogenboom, 2022; Rades et al, 2022; van Woesik et al, 2022).…”