The ocean is changing rapidly – it is becoming more acidic and warmer at increasingly fast rates. As humans release more carbon dioxide (CO2), it dissolves into the ocean, where it decreases the pH and carbonate ion concentration of the seawater, and it warms the Earth’s surface (IPCC, 2007). Coral are particularly vulnerable to rises in acidity and temperature. Most studies that examine biological responses of coral to these future ocean conditions focus on calcification of coral skeletons and/or photosynthesis by the single-celled algae that live inside the coral (e.g. Reynaud, 2003; Anthony et al. 2008). Though it has never before been examined in the context of ocean acidity and temperature in combination, maintenance of other aspects of the cell environment such as oxidative state and ionic balance will be affected by future ocean conditions. Ocean acidity and elevated temperature likely increase the formation of reactive oxygen species (ROS), modified oxygen molecules that readily react with and thus damage other molecules in cells, thereby compromising cellular oxidative state. To neutralize the ROS, cells activate their stress response pathways, a battery of proteins and other molecules that defend cellular machinery against oxidative damage (reviewed in Kültz, 2005). Ocean acidification and warming may also increase the cost of maintaining the proper balance of ions inside and outside of the cells of the larvae. An enzyme, Na+/K+-ATPase, is largely responsible for maintaining these gradients (e.g. Melzner et al. 2009), and its activity in response to future ocean conditions was a focus during this project. The hard coral Pocillopora damicornis suited these studies due to its wide abundance throughout the Indo-Pacific region. If its larvae (swimming young) cannot tolerate ocean acidification and elevated temperature, the distribution and even survival of the species will be affected. To investigate whether ocean acidity and temperature interact to increase maintenance of oxidative state and ionic balance, P. damicornis larvae were incubated in seawater with CO2 concentrations and temperatures to represent current and future levels of CO2 and temperature predicted by the end of this century. At the National Museum of Marine Biology and Aquarium (NMMBA) in southern Taiwan, ~65,000 P. damicornis larvae were collected from 16 wild-caught colonies as they were released according to the lunar cycle. Following the incubations, larvae were frozen and then analyzed using a variety of assays to evaluate their response to oxidative stress and their maintenance of ionic balance. Preliminary data suggest that ocean acidification generates oxidative stress in P. damicornis larvae. While it consumes a lot of energy to do so, these larvae combat reactive oxygen species (ROS) within their cells when exposed to high CO2 conditions. However, the larvae vary in their ability to neutralize ROS depending upon which day they are released from the adult coral. Clearly, a stress response to increases in ROS is a costly adjustment to the energy budget of these larvae but one that is required for survival in future ocean conditions. Specific larval responses to oxidative stress from ocean acidification will be the focus of future work. The results of this study can be used for much comparative and predictive work. Protocols developed in this project can be used to compare populations of P. damicornis throughout the Indo-Pacific region to see how response to ROS generated by ocean acidification and elevated temperature varies across the species distribution. P. damicornis is considered a robust coral species, often growing in sub-optimal conditions with higher temperatures and cloudier water. By examining the strength of larval response to oxidative stress, this research can be applied to identify sites where P. damicornis is more tolerant, allowing for preservation of these populations and formation of refuges. This study could be applied to less hardy species to gain insight of their current abilities to adjust to and tolerate future ocean conditions. Anthony, KRN, DI Kline, G Diaz-Pulido, S Dove, and O Hoegh-Guldberg. 2008. Ocean acidification causes bleaching and productivity loss in coral reef builders. Proc Nat Acad Sci 105:17442-17446. IPCC. 2007. Summary for Policymakers. In Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Solomon, S, D Qin, M Manning, Z Chen, M Marquis, KB Averyt, M Tignor, and HL Miller (eds). Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA. Kültz, D. 2005. Molecular and evolutionary basis of the cellular stress response. Annu Rev Physiol 67:225-257. Melzner, F, S Göbel, M Langenbuch, MA Gutowska, H-O Pörtner, and M Lucassen. 2009. Swimming performance in Atlantic Cod (Gadus morhua) following long-term (4-12 months) acclimation to elevated seawater PCO2. Aquat Toxicol 92:30-37. Reynaud, S, N Leclercq, S Romaine-Lioud, C Ferrier-Pages, J Jaubert, and J-P Gattuso. 2003. Interacting effects of pCO2 partial pressure and temperature on photosynthesis and calcification in a scleractinian coral. Glob Change Biol 9:1660-1668.
