Abstract
Ocean acidification (OA) is negatively affecting calcification in a wide variety of marine organisms. These effects are acute for many tropical scleractinian corals under short-term experimental conditions, but it is unclear how these effects interact with ecological processes, such as competition for space, to impact coral communities over multiple years. This study sought to test the use of individual-based models (IBMs) as a tool to scale up the effects of OA recorded in short-term studies to community-scale impacts, combining data from field surveys and mesocosm experiments to parameterize an IBM of coral community recovery on the fore reef of Moorea, French Polynesia. Focusing on the dominant coral genera from the fore reef, Pocillopora, Acropora, Montipora and Porites, model efficacy first was evaluated through the comparison of simulated and empirical dynamics from 2010–2016, when the reef was recovering from sequential acute disturbances (a crown-of-thorns seastar outbreak followed by a cyclone) that reduced coral cover to ~0% by 2010. The model then was used to evaluate how the effects of OA (1,100–1,200 µatm pCO2) on coral growth and competition among corals affected recovery rates (as assessed by changes in % cover y−1) of each coral population between 2010–2016. The model indicated that recovery rates for the fore reef community was halved by OA over 7 years, with cover increasing at 11% y−1 under ambient conditions and 4.8% y−1 under OA conditions. However, when OA was implemented to affect coral growth and not competition among corals, coral community recovery increased to 7.2% y−1, highlighting mechanisms other than growth suppression (i.e., competition), through which OA can impact recovery. Our study reveals the potential for IBMs to assess the impacts of OA on coral communities at temporal and spatial scales beyond the capabilities of experimental studies, but this potential will not be realized unless empirical analyses address a wider variety of response variables representing ecological, physiological and functional domains.
Highlights
Evaluation of the effects of ocean acidification (OA) on marine organisms (Kroeker et al, 2010; Wittmann & Pörtner, 2013) supports the general conclusion that biogenic calcification will be depressed by rising seawater pCO2 (Chan & Connolly, 2013; Kornder, Riegl & Figueiredo, 2018; Kroeker et al, 2013)
The present study utilizes an individual-based models (IBMs) developed for a fore reef coral community to evaluate how the effects of OA (i.e., ~1,100–1,200 μatm pCO2) on coral growth and competition among corals scale up to impact the projected rate of increase in coral cover following a major disturbance
Under current ambient pCO2, the coral community at 10-m depth on the fore reef of Moorea has quickly recovered from recent disturbances, with coral cover rising from 0.3% in 2010 to 66% in 2016, primarily through high recruitment of Pocillopora (Tsounis & Edmunds, 2016; Edmunds, 2018b)
Summary
Evaluation of the effects of ocean acidification (OA) on marine organisms (Kroeker et al, 2010; Wittmann & Pörtner, 2013) supports the general conclusion that biogenic calcification will be depressed by rising seawater pCO2 (Chan & Connolly, 2013; Kornder, Riegl & Figueiredo, 2018; Kroeker et al, 2013). Beyond affecting vital rates (like recruitment), elevated pCO2 has the potential to alter the synecology of coral reefs, for example, by altering competitive dynamics between corals and algae (Diaz-Pulido et al, 2011), as well as among corals (Evensen & Edmunds, 2016; Horwitz, Hoogenboom & Fine, 2017). It is challenging, to predict how the effects of OA on ecological and demographic processes will scale up to affect coral community dynamics (Albright & Langdon, 2011; Edmunds et al, 2016a). The most ambitious predictions require consideration of the potential for acclimatization or adaptation (Schoepf et al, 2017; Kurihara et al, 2020)
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