PH up-regulation as a potential mechanism for the cold-water coral &amp;lt;i&amp;gt;Lophelia pertusa&amp;lt;/i&amp;gt; to sustain growth in aragonite undersaturated conditions

M Wall,A Form,D N Schmidt,L C Foster,F Ragazzola

doi:10.5194/bg-12-6869-2015

Abstract

Abstract. Cold-water corals are important habitat formers in deep-water ecosystems and at high latitudes. Ocean acidification and the resulting change in aragonite saturation are expected to affect these habitats and impact coral growth. Counter to expectations, the deep water coral Lophelia pertusa has been found to be able to sustain growth even in undersaturated conditions. However, it is important to know whether such undersaturation modifies the skeleton and thus its ecosystem functioning. Here we used Synchrotron X-Ray Tomography and Raman spectroscopy to examine changes in skeleton morphology and fibre orientation. We combined the morphological assessment with boron isotope analysis to determine if changes in growth are related to changes in control of calcification pH. We compared the isotopic composition and structure formed in their natural environment to material grown in culture at lower pH conditions. Skeletal morphology is highly variable but shows no distinctive differences between natural and low pH conditions. Raman investigations found no difference in macromorphological skeletal arrangement of early mineralization zones and secondary thickening between the treatments. The δ11B analyses show that L. pertusa up-regulates the internal calcifying fluid pH (pHcf) during calcification compared to ambient seawater pH and maintains a similar elevated pHcf at increased pCO2 conditions. We suggest that as long as the energy is available to sustain the up-regulation, i.e. individuals are well fed, there is no detrimental effect to the skeletal morphology.

Highlights

The ocean is absorbing CO2 from anthropogenic emissions resulting in a drop in carbonate saturation and ocean pH (Bates et al, 2012)
The Raman maps clearly display the orientation of the skeletal fibres and the location of the early mineralization zone (EMZ: Cuif and Dauphin, 2005, or rapid accretion front, RAF: Stolarski, 2003) and were used to compare skeletal formation before and during experimental conditions (Fig. 2c, d)
Lophelia pertusa has been shown to grow in undersaturated conditions

Summary

Introduction

The ocean is absorbing CO2 from anthropogenic emissions resulting in a drop in carbonate saturation and ocean pH (Bates et al, 2012). The response of marine calcifiers to ocean acidification has been shown to be taxon-specific (e.g. Ries et al, 2009; Pörtner et al, 2014); understanding the response of important key marine habitat builders is imperative to estimate potential impacts on their future ecosystem service. Cold-water corals are important habitat builders that offer a range of microhabitats sustaining high biodiversity and provide nursery grounds for various species of fish (Fosså et al, 2002; Henry and Roberts, 2007; Roberts et al, 2008). The maintenance of their structural integrity is essential not just for the species itself and for a wide range of species which depend on this habitat.

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Results

Conclusion