ORIGINAL PAPER Ocean warming and acidification; implications for the Arctic brittlestar Ophiocten sericeum Hannah L. Wood • J. I. Spicer • M. A. Kendall • D. M. Lowe • S. Widdicombe Received: 5 October 2010 / Revised: 5 January 2011 / Accepted: 6 January 2011 / Published online: 2 February 2011 Ó Springer-Verlag 2011 Abstract The Arctic Ocean currently has the highest global average pH. However, due to increasing atmo- spheric CO 2 levels, it will become a region with one of the lowest global pH levels. In addition, Arctic waters will also increase in temperature as a result of global warming. These environmental changes can pose a significant threat for marine species, and in particular true Arctic species that are adapted to the historically cold and relatively stable abiotic conditions of the region. Consequently, we inves- tigated some key physiological responses of brittlestar Ophiocten sericeum, a polar endemic which can dominate benthic infauna, to a temperature increase of 3.5°C (ambient, 5–8.5°C) and CO 2 induced reduction in pH of 0.6 units (pH 7.7) and 1 unit (pH 7.3) below ambient (pH 8.3). Metabolism was upregulated at low pH. Faster arm regeneration stimulated by increased temperature was counteracted by low pH; at pH 7.3 in the high-temperature treatment, the maintenance of calcium carbonate structures in undersaturated conditions resulted in reduction in the rate of arm regeneration, possibly due to accelerated the use of energy reserves. If so, this could result in an energy deficit at times of increased energetic costs associated with responding to the combined factors of high temperature and low pH. Keywords Ocean acidification  Svalbard  Physiology  Brittlestar  Ophiocten sericeum  Temperature  pH Introduction Average sea surface temperature is now 0.6°C warmer than at the start of the industrial revolution (IPCC 2001), and a further increase of 3–6°C is forecast by the end of this century (MCCIP 2008). Marine Arctic ecosystems are already experiencing some measurable changes as a result of this warming (Hu and Pan 2009). On the ‘warmer’ west side of Svalbard, many glaciers are retreating and decreasing in mass balance, changes linked to increases in temperature (Wright et al. 2006), and winter fjord ice cover is no longer guaranteed; Kongsfjord did not freeze over between 2005 and 2008 where this was once a regular occurrence. In addition to increasing temperatures, the Arctic is also at the forefront of the threat posed by ocean acidification. It is projected that 10% of Arctic waters will become undersaturated with respect to 9 X arag for at least 1 month a year when atmospheric CO 2 concentrations reach 409 ppm. It is estimated that this will occur within the next decade (IPCC scenarios A2 & B1), and complete undersaturation of the water column is predicted before the end of this century (Steinacher et al. 2009). While polar waters cur- rently have the highest global average pH, the largest pH changes in ocean pH will occur in the Arctic Ocean (Steinacher et al. 2009), resulting in one of the lowest global pH averages. Furthermore, in these regions, increasing temperature and ocean acidification are H. L. Wood  M. A. Kendall  D. M. Lowe  S. Widdicombe Plymouth Marine Laboratory, Prospect Place, West Hoe, Plymouth PL1 3DH, UK J. I. Spicer Marine Biology & Ecology Research Centre, School of Marine Science & Engineering, University of Plymouth, Plymouth PL4 8AA, UK H. L. Wood (&) Department of Marine Ecology, Go ¨teborg University, Sven Love ´n Centre for Marine Sciences, Kristineberg 45034, Sweden e-mail: hannah.wood@marecol.gu.se 123 Polar Biol (2011) 34:1033–1044 DOI 10.1007/s00300-011-0963-8