Abstract
Abstract. Coral reefs are diverse ecosystems that are threatened by rising CO2 levels through increases in sea surface temperature and ocean acidification. Here we present a new unified model that links changes in temperature and carbonate chemistry to coral health. Changes in coral health and population are explicitly modelled by linking rates of growth, recovery and calcification to rates of bleaching and temperature-stress-induced mortality. The model is underpinned by four key principles: the Arrhenius equation, thermal specialisation, correlated up- and down-regulation of traits that are consistent with resource allocation trade-offs, and adaption to local environments. These general relationships allow this model to be constructed from a range of experimental and observational data. The performance of the model is assessed against independent data to demonstrate how it can capture the observed response of corals to stress. We also provide new insights into the factors that determine calcification rates and provide a framework based on well-known biological principles to help understand the observed global distribution of calcification rates. Our results suggest that, despite the implicit complexity of the coral reef environment, a simple model based on temperature, carbonate chemistry and different species can give insights into how corals respond to changes in temperature and ocean acidification.
Highlights
Coral reefs are among the world’s most biologically complex ecosystems; they support a diverse range of species and provide critically important ecosystem services such as food, resources for livelihoods and coastal protection
The goal of this work is to provide a simple description of these processes that is motivated by the underlying physiological mechanisms and, where possible, to validate these against experimental observations
Calcification of the coral Acropora eurystoma was measured as a function of aragonite saturation state and temperature
Summary
Coral reefs are among the world’s most biologically complex ecosystems; they support a diverse range of species and provide critically important ecosystem services such as food, resources for livelihoods and coastal protection. At present coral reefs face an unprecedented rate of environmental change in response to increasing atmospheric greenhouse gases and especially carbon dioxide (CO2; IPCC, 2014). Two of the most immediate impacts of rising CO2 levels on coral reefs are increases in ocean temperatures and ocean acidification (Hoegh-Guldberg, 2011; Doney et al, 2009). As coral’s skeletons are made from the mineral phase of calcium carbonate, called aragonite, the saturation state of aragonite ( arg) is often related to rates of calcification. As CO2 concentrations rise, the saturation state of aragonite ( arg) decreases and, in turn, the rate at which corals calcify declines (Schneider and Erez, 2006; Langdon, 2005; Pandolfi et al, 2011; Venn et al, 2013). Projections suggest that future rates of coral reef community dissolution may exceed rates of CaCO3 production (calcification), leading to net loss
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