Ocean Acidification and Coral Reefs: Effects on Breakdown, Dissolution, and Net Ecosystem Calcification

Abstract

The persistence of carbonate structures on coral reefs is essential in providing habitats for a large number of species and maintaining the extraordinary biodiversity associated with these ecosystems. As a consequence of ocean acidification (OA), the ability of marine calcifiers to produce calcium carbonate (CaCO3) and their rate of CaCO3 production could decrease while rates of bioerosion and CaCO3 dissolution could increase, resulting in a transition from a condition of net accretion to one of net erosion. This would have negative consequences for the role and function of coral reefs and the eco-services they provide to dependent human communities. In this article, we review estimates of bioerosion, CaCO3 dissolution, and net ecosystem calcification (NEC) and how these processes will change in response to OA. Furthermore, we critically evaluate the observed relationships between NEC and seawater aragonite saturation state (Ωa). Finally, we propose that standardized NEC rates combined with observed changes in the ratios of dissolved inorganic carbon to total alkalinity owing to net reef metabolism may provide a biogeochemical tool to monitor the effects of OA in coral reef environments.

Multiple driving factors explain spatial and temporal variability in coral calcification rates on the Bermuda platform

“…Warmer temperatures result in lower solubility of CO 2 in seawater and lower aragonite solubility, which contribute to an increase in seawater X arag . Increasing solar irradiance also affects net community production and calcification, which could alter X arag depending on the relative uptake of DIC and TA (Andersson and Gledhill 2013). We discuss the cause and effect between these changes and the calcification rates of the corals in the subsequent discussion.…”

“…Consequently, the potential for a spatial gradient in carbon chemistry across the Bermuda reef platform seems likely. However, have shown that despite a strong seasonal and spatial signal in the distributions of total alkalinity (TA) and dissolved inorganic carbon (DIC), only relatively small spatial gradients in pH and X arag are observed across the platform due to the nearly proportional changes in DIC and TA owing to net reef metabolism (i.e., net ecosystem production, NEP = primary production -autotrophic and heterotrophic respiration; net ecosystem calcification, NEC = calcificationCaCO 3 dissolution; Andersson and Gledhill 2013 Fig. 1).…”

“…This is not significantly different from the 1.05 ± 0.04 reported by . This means that the biota on the platform is removing DIC and TA from the water in a fairly constant ratio both temporally and spatially and that this ratio balances the effect of photosynthesis to elevate pH (reduce pCO 2 ) and calcification to reduce pH (elevate pCO 2 ; Andersson and Gledhill 2013). When the two processes combine in this ratio, the DIC and TA can be drawn far down from their source water values without altering the pH, pCO 2 , or X arag significantly.…”

Spatiotemporal Assessment of CO2–Carbonic Acid System Dynamics in a Pristine Coral Reef Ecosystem, French Frigate Shoals, Northwestern Hawaiian Islands

“…Photosynthesis during the day consumes DIC and increases X ar , which promotes calcification that depletes TA (Suzuki et al 1995;Ohde and van Woesik 1999;Bates et al 2010;Shamberger et al 2011;Lantz et al 2013). At night, respiration produces CO 2 , decreases X ar , and calcification often slows, with some benthic communities experiencing net dissolution Halley 2003, 2006;Andersson and Gledhill 2013;Eyre et al 2014). The impact of these processes on the variability in the parameters of the CO 2 -carbonic acid system depends on a number of environmental factors including geographic location, seasonal and daily trends in temperature and light availability, hydrodynamic forcing and nutrients (Suzuki et al 1995;Andersson et al 2005;Bates et al 2010;Drupp et al 2011Drupp et al , 2013Falter et al 2012;Zhang et al 2012;Yeakel et al 2015).…”

“…The DTA: DDIC relationship reflects the balance between net ecosystem calcification (NEC) and net primary production (NPP) (Gattuso et al 1996;Watanabe et al 2006;Andersson and Gledhill 2013;Lantz et al 2013;Mackenzie and Andersson 2013). If TA and DIC decrease at a rate greater than one, calcification exceeds primary production and if TA and DIC decrease at a rate less than one, primary production exceeds calcification.…”