ORIGINAL PAPER Occurrence of a cold-water coral along natural pH gradients (Patagonia, Chile) C. Jantzen • V. Ha ¨ussermann • G. Fo ¨rsterra • J. Laudien • M. Ardelan • S. Maier • C. Richter Received: 1 November 2012 / Accepted: 29 April 2013 / Published online: 15 May 2013 Ó Springer-Verlag Berlin Heidelberg 2013 Abstract Increasing dissolution of anthropogenic-released carbon dioxide into the world’s oceans is causing ocean acidification (OA). OA is thought to negatively affect most marine-calcifying organisms, notably cold-water corals (CWC), which may be especially sensitive due to the deep and cold waters they normally thrive in. However, the impact of OA on CWC is difficult to predict. Recorded distributions of CWC are rarely linked to in situ water chemistry, and the boundaries of their distributions are not clearly defined. The fjord Comau in Chilean Patagonia features pronounced pH gradients, and up to 0.5 pH units have been recorded both vertically (at some sites within 50 m depth) and less distinct horizontally (from head to mouth). The cosmopolite coral Desmophyllum dianthus grows along the course of the fjord and of the entire pH range. It occurs in shallow depths (below 12 m, pH 8.1) as part of a deep-water emergence community, but also in 225 m depth at a pH of 7.4. Based on pH and total alkalinity, data calculations of the associated carbonate chemistry revealed that this CWC thrives commonly close the aragonite (the orthogonal crystal form of calcium carbonate, the mineral structure of coral skeletons) saturation horizon and even below. This suggests a high adaptation potential of D. dianthus to adjust its calcification performance to condi- tions thermodynamically unfavourable for the precipitation of aragonite. Introduction The changing conditions of the oceans caused by increasing anthropogenic carbon dioxide (CO 2 ) emissions and the ensuing ocean acidification (OA, Crowley 2000; Caldeira and Wickett 2005) raised growing concern in the scientific com- munity about the fate of our world’s oceans and their marine life (e.g. Ve ´zina and Hoegh-Guldberg 2008; De’ath et al. 2009; Fabricius et al. 2011; Venn et al. 2013). The impacts of OA on organisms are difficult to predict, and most is still left to speculation (e.g. Hoegh-Guldberg 1999; Orr et al. 2005). This is, to some extent, due to the complex nature of the sea water carbonate buffer system and the associated difficulties in evaluating the dynamics involved (Falkowski et al. 2000; Caldeira and Wickett 2005). As calcium carbonate (CaCO 3 ) precipitation may be linked to the prevailing carbonate chemistry within sea water, the process of calcification by marine organisms may be particularly influenced by OA (e.g. Doney et al. 2009; De’ath et al. 2009). Calcareous structures such as skeletons, shells and prickles are built-ups by calcium (Ca 2? ) and carbonate ions (CO 3 2- ); the latter is part of the carbonate buffer system of sea water (Millero 2006). Coral skeletons are made of aragonite, the orthogonal crystal form of calcium carbonate (Meibom et al. 2007), Communicated by R. Hill. Electronic supplementary material The online version of this article (doi:10.1007/s00227-013-2254-0) contains supplementary material, which is available to authorized users. C. Jantzen (&) Á J. Laudien Á S. Maier Á C. Richter Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Am Alten Hafen 26, 27568 Bremerhaven, Germany e-mail: carin.jantzen@awi.de V. Ha ¨ussermann Á G. Fo ¨rsterra Facultad de Recursos Naturales, Escuela de Ciencias del Mar, Pontificia Universidad Catolica de Valparaıso, Avda. Brasil 2950, Valparaiso, Chile M. Ardelan Department of Chemistry, Norwegian University of Science and Technology, 7491 Trondheim, Norway 123 Mar Biol (2013) 160:2597–2607 DOI 10.1007/s00227-013-2254-0