1 3 Mar Biol DOI 10.1007/s00227-015-2617-9 SHORT NOTE Species-specific differences in thermal tolerance may define susceptibility to intracellular acidosis in reef corals Emma M. Gibbin · Hollie M. Putnam · Ruth D. Gates · Matthew R. Nitschke · Simon K. Davy Received: 29 August 2014 / Accepted: 16 January 2015 © Springer-Verlag Berlin Heidelberg 2015 placed them in a live-cell chamber attached to a confocal microscope and bathed them in CO 2 -acidified seawater (~pH 7.6) for 30 min, before measuring the light-adapted pH i of both the host cell and its symbiont. Cells isolated from P. damicornis were more prone to cellular acido- sis (declines in pH i of 11 and 8 % in host and symbiont, respectively, at 31 °C relative to 23.8 °C) than cells isolated from M. capitata (5 and 4 %, respectively). These results highlight the important role of Symbiodinium productivity (in addition to a range of physico-chemical factors such as skeletal morphology and tissue pigmentation) in determin- ing the sensitivity of corals to rising sea surface tempera- tures and ocean acidification. Introduction Post-industrial atmospheric CO 2 levels are increasing at a rate and magnitude that is unparalleled in recent geological history. To date this has resulted in a 1–2 °C increase in the global mean temperature and a 0.08 reduction in oceanic surface water pH, from 8.13 to the present day 8.05 (IPCC 2014). The combination of increasing temperature, declin- ing pH and a reduction in the amount of available car- bonate via ocean acidification is predicted to have severe consequences for calcifying species, potentially leading to phase shifts towards ecosystems dominated by algal- or soft-bodied organisms (Bell et al. 2013). Coral reefs are already showing signs of demise, particularly in areas that are subjected to sustained periods of exposure to warm water (Carpenter et al. 2008). Chronic stress often results in the photosynthetic dysfunction and subsequent loss of single-celled symbiotic dinoflagellates (Symbiodinium sp.) and/or their photosynthetic pigments (Weis 2008). This collapse in symbiosis, a process termed “coral bleaching”, Abstract It is widely acknowledged that temperature stress affects an organism’s sensitivity to ocean acidifi- cation and vice versa, yet it is not clear how the two are mechanistically linked. Here, we induced thermal stress in two coral species with differing bleaching susceptibilities to measure how a reduction in photosynthetic performance impacts intracellular pH (pH i ) regulation in the symbiotic dinoflagellates (Symbiodinium sp.) and their host coral cells. Our hypothesis was that thermally induced photo- synthetic dysfunction in the symbiont would prevent the efficient removal of additional CO 2 , lowering its buffering capacity and thus increasing the host cell’s susceptibility to intracellular acidosis. To test this, we exposed Pocillopora damicornis (a thermally sensitive coral) and Montipora capitata (a thermally resilient coral) to four different tem- perature treatments (23.8, 25.5, 28 and 31 °C) for 1 week. We then isolated intact symbiotic coral endodermal cells, Communicated by R. Hill. Electronic supplementary material The online version of this article (doi:10.1007/s00227-015-2617-9) contains supplementary material, which is available to authorized users. E. M. Gibbin · S. K. Davy (*) School of Biological Sciences, Victoria University of Wellington, Kelburn Parade, Wellington 6140, New Zealand e-mail: simon.davy@vuw.ac.nz E. M. Gibbin e-mail: emma.gibbin@hotmail.co.uk H. M. Putnam · R. D. Gates Hawaii Institute of Marine Biology, University of Hawaii, PO Box 1346, Kaneohe, HI 96744, USA M. R. Nitschke School of Biological Sciences, The University of Queensland, St Lucia, Brisbane, QLD 4072, Australia