Ocean acidification affects coral growth by reducing skeletal density

Abstract

Ocean acidification (OA) is considered an important threat to coral reef ecosystems, because it reduces the availability of carbonate ions that reef-building corals need to produce their skeletons. However, while theory predicts that coral calcification rates decline as carbonate ion concentrations decrease, this prediction is not consistently borne out in laboratory manipulation experiments or in studies of corals inhabiting naturally low-pH reefs today. The skeletal growth of corals consists of two distinct processes: extension (upward growth) and densification (lateral thickening). Here, we show that skeletal density is directly sensitive to changes in seawater carbonate ion concentration and thus, to OA, whereas extension is not. We present a numerical model of skeletal growth that links skeletal density with the external seawater environment via its influence on the chemistry of coral calcifying fluid. We validate the model using existing coral skeletal datasets from six species collected across five reef sites and use this framework to project the impact of 21st century OA on skeletal density across the global tropics. Our model predicts that OA alone will drive up to 20.3 ± 5.4% decline in the skeletal density of reef-building corals.

The Origin of the Subtropical Coral Alveopora japonica (Scleractinia: Acroporidae) in High-Latitude Environments

“…Northward range shifts, i.e., range expansions in response to rising sea surface temperatures, have also been frequently reported for tropical reef scleractinian corals (Precht and Aronson, 2004;Greenstein and Pandolfi, 2008;Yamano et al, 2011). In addition to poleward migration, climate changes have strong negative impacts on the scleractinian corals even in temperate areas, as they may suffer from ocean acidification in the future (Mollica et al, 2018). However, climate changes can also have positive effects on population growth (i.e., population expansion) of corals via modulating growth, reproduction and recruitment (Denis et al, 2014;Vieira et al, 2016) or by creating novel coral assemblages sometimes resistant to disease (Yakob and Mumby, 2011), particularly in temperate regions.…”

Environmental and physiochemical controls on coral calcification along a latitudinal temperature gradient in Western Australia

“…In addition to ocean warming, increasing CO 2 is driving declines in seawater pH and thus seawater aragonite saturation state (Ω = [][Ca 2+ ]/ K sp ). OA can result in morphological deformities in juvenile corals (Cohen, McCorkle, de Putron, Gaetani, & Rose, ; Foster, Falter, McCulloch, & Clode, ) and a reduction in coral calcification rates for some adult corals (e.g., Crook, Cohen, Rebolledo‐Vieyra, Hernandez, & Paytan, ; Jokiel et al, ; Marubini et al, ; Marubini, Ferrier‐Pagès, & Cuif, ; Mollica et al, ), although this is not always the case (e.g., Comeau et al, ; Comeau, Cornwall, DeCarlo, Krieger, & McCulloch, ; Jury, Whitehead, & Szmant, ; Schoepf et al, ). Variation in the responses of coral calcification to OA can be explained by differences in species, life stage, food availability, growth form (e.g., Albright & Langdon, ; Cohen & Holcomb, ; Kornder, Riegl, & Figueiredo, ), and bio‐calcification mechanisms (e.g., Comeau et al, ; DeCarlo, Comeau, Cornwall, & McCulloch, ; Georgiou et al, ; Schoepf, Jury, Toonen, & McCulloch, ).…”

Paradise lost: End‐of‐century warming and acidification under business‐as‐usual emissions have severe consequences for symbiotic corals

“…In bleached A. intermedia , G TA was negative, despite average seawater Ω ARAG values of 3.39 (Table ) and daytime G TA was not reduced in either species as long as photosynthetic rates were maintained (Levas et al, ). The constraints of elevated temperature and acidification on long‐ and short‐term measures of skeleton growth will, provided that corals survive, limit reef capacity to outpace sea‐level rise and decrease resilience to extreme weather (Manzello et al, ; Mollica et al, ; van Woesik et al, ).…”