Meta-Analysis Reveals Reduced Coral Calcification Under Projected Ocean Warming but Not Under Acidification Across the Caribbean Sea

Abstract

Ocean acidification and warming are two of the many threats to coral reefs worldwide, and Caribbean reef-building corals are especially vulnerable. However, even within the Caribbean, experimental acidification and warming studies reveal a wide array of coral calcification responses across reef systems and among species, complicating efforts to predict how corals will respond to these global-scale stressors. We conducted a meta-analysis to investigate the calcification responses of Caribbean corals to experimentally induced seawater ocean acidification, ocean warming, and the combination of both stressors. Calcification rates were reduced for corals reared under warming alone, but acidification and the combination of both stressors did not clearly reduce calcification rates. Calcification responses of corals collected from the Florida Keys and Belize were compared for regional differences since a greater number of studies were performed on corals collected from these two regions. Notably, corals from the Florida Keys did not exhibit reduced calcification under acidification, warming, or the combination of both stressors, while corals from Belize exhibited reduced calcification under warming alone. Further investigation of these regional trends suggests that the warming and acidification treatments employed dictated calcification responses, rather than collection region. Results from this meta-analysis are constrained by the very few studies that have been conducted within the Caribbean to assess ocean acidification and warming and the large variation in experimental procedure among studies. This meta-analysis reveals existing gaps in our understanding of how corals will likely respond to projected acidification and warming and highlights ways to improve comparability among experimental studies conducted on corals within the same region to better predict coral calcification response under global change.

Important ecosystem function, low redundancy and high vulnerability: The trifecta argument for protecting the Great Barrier Reef's tabular Acropora

“…The effect of ocean acidification (OA) on corals and particularly on calcification rates has been the focus of intense debate (Bove et al., 2020; Mollica et al., 2018). Although some studies have identified internal upregulation of pH as an acclimatory mechanism for coral to overcome the effect of OA (McCulloch et al., 2012), recent laboratory studies have challenged the magnitude of resistance that this mechanism may provide (Comeau et al., 2019).…”

Global coral reef ecosystems exhibit declining calcification and increasing primary productivity

“…Similarly, when all previous sitespecific models that use physicochemical parameters to predict G net were compiled, the only model to significantly correlate with global G net observations relied on temperature alone 42,67 . In general, increasing temperatures increase coral growth until a thermal threshold is reached 29 . The magnitude of this effect can be dependent on species, location or latitude 56,91 .…”

“…Higher rates of G net tend to indicate reefs with higher coral cover 9,21,22 , and ecosystems which have not been impacted by significant stressors [23][24][25][26] , whereas declining and net-dissolving calcification rates indicate stressed corals 16,18,27 or ecosystems which have little to no live corals 25,28 . Therefore, G net and P net are increasingly used as proxies for coral reef ecosystem health 10,29,30 .…”

“…However, mesocosms may not reflect in situ conditions because they cannot capture the rich natural complexity inherent in coral reef ecosystems 39,40 . Predicting G net as a function of environmental parameters is difficult, and relationships produced at local scales or in mesocosm experiments may not be accurate at broader spatial scales or over time 9,29,41,42 . Thus, a meta-analyses approach can help to elucidate key drivers of global coral ecosystem calcification and understand how G net may respond to changing environmental conditions.…”

The role of soils in the regulation of ocean acidification

“…Research over the last 20 years to understand the impact of ocean acidification [84] has produced variable results [90,91]. Species that can maintain calcium carbonate saturation levels in their internal calcifying sites may be less affected by changes in seawater pH.…”