Effects of chronic low carbonate saturation levels on the distribution, growth and skeletal chemistry of deep-sea corals and other seamount megabenthos

Abstract

Ocean acidification has been predicted to reduce the ability of marine organisms to produce carbonate skeletons, threatening their long-term viability and severely impacting marine ecosystems. Corals, as ecosystem engineers, have been identified as particularly vulnerable and important. To determine the sensitivity of corals and allied taxa to long-term exposure to very low carbonate concentrations, we examined the distribution and skeletal characteristics of coral taxa along a natural deep-sea concentration gradient on seamounts of SW Australia. Carbonate undersaturation had little evident effect on the depth distribution, growth or skeletal composition of live scleractinians or gorgonians, with corals growing, often abundantly, in waters as much as 20 to 30% under-saturated. Developmental anomalies in the deepest skeleton-forming anthozoan collected (an isidid gorgonian, at nearly 4 km depth) suggest an absolute low tolerance limit of about 40% under-saturation. Evidence for an effect of acidification on the accumulation of reef structure is ambiguous, with clear indications of dissolution of high-magnesium calcite (HMC) gorgonian skeletons at depths below 2300 m, but also abundant, old scleractinian skeletons well below the aragonite saturation horizon. The latter might be the result of ferromanganese deposition on exposed skeletons, which, however, may render them inhospitable for benthic organisms.KEY WORDS: Anthozoa · Echinoderm · Aragonite saturation horizon · Calcite saturation horizon · Gorgonacea · High-magnesium calcite · Mineralogy · Scleractinia Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 442: [87][88][89][90][91][92][93][94][95][96][97][98][99] 2011 that are more resilient or lack carbonate skeletons; and reduced long-term viability due to the additional stress imposed on reef taxa by changing carbonate concentrations (Hoegh-Guldberg et al. 2007, Guinotte & Fabry 2008, Riegl et al. 2009, Veron et al. 2009). If reef ecosystems degrade as predicted under present 'business-as-usual' scenarios, the impacts on global biodiversity and regional economies will be profound.Coral reefs in the deep sea have been identified as particularly vulnerable, due to low pre-industrial carbonate levels in their environment that will potentially be reduced even further as a result of climate change (Guinotte et al. 2006, Turley et al. 2007, Riegl et al. 2009). Direct tests of this sensitivity have not been done, but in at least one relatively shallow coldwater coral, Lophelia pertusa, calcification rates decline as predicted under low pH conditions (Maier et al. 2009). Deep-water corals may often also have very limited scope for vertical adjustment, potentially being squeezed between seamount summits on the one hand and shoaling saturation horizons on the other. Even the tops of many seamounts that currently support deep-sea coral communities may well be under-saturated in the next 50 to 100 yr. With nowhere to go, these cold-water reefs could 'simply disa...

Coral Reef Ecosystems under Climate Change and Ocean Acidification

“…It will also be important to get a better understanding of how environmental conditions differ in the case of mesophotic reefs and whether or not they have the potential to act as refugia for coral reef species from the greater environmental extremes of shallow regions (Bongaerts et al, 2010a(Bongaerts et al, , 2013(Bongaerts et al, , 2015. With regard to cold-water corals, management interventions are likely to be limited to regulating or banning fishing and mineral extraction in the locality of reefs (Thresher et al, 2011). The highest priority for these sensitive ecosystems is to locate and protect sites that are likely to be refugia areas (Thresher et al, 2015).…”

Resistance of Two Mediterranean Cold-Water Coral Species to Low-pH Conditions

“…This would be the case of cold-water coral (CWC) communities, which are found in areas characterised by very low aragonite saturation state values (Ω A ) [12,13]. Therefore, studies evaluating the potential impact of OA on CWC populations are essential to determine the future of one of the most complex deep-sea habitats in the Mediterranean Sea.…”

The influence of seawater pH on U / Ca ratios in the scleractinian cold-water coral <i>Lophelia pertusa</i>

“…Case et al, 2010;Cohen et al, 2006;Gagnon et al, 2007;Lutringer et al, 2005;Montagna et al, 2006;Raddatz et al, 2013;RollionBard et al, 2009;Rüggeberg et al, 2008;Smith et al, 2000). To date only a few studies have focused on the reconstruction of the carbonate system using CWC skeletons (Anagnostou et al, 2011(Anagnostou et al, , 2012Blamart et al, 2007;McCulloch et al, 2012;Rollion-Bard et al, 2011a, b;Thresher et al, 2011). Coral uranium to calcium (U / Ca) ratios are known to depend on the carbonate system parameters (Anagnostou et al, 2011;Inoue et al, 2011;Min et al, 1995;Shen and Dunbar, 1995;Swart and Hubbard, 1982).…”