Can corals acclimate to the high CO2 world?

Chair: Sean Connell

Haruko Kurihara (1), Asami Tsugi (1), Takashi Kawai (1), Izumi Mimura (1), Chuki Hongo (1), Atsushi Watanabe (2), Marine Gouezo (3), Yimnang Golbuu (3)

1 University of the Ryukyus, Okinawa, 903-0213, Japan
2 Tokyo Institute of Technology, Tokyo, 152-8552, Japan
3 Palau International Coral Reef Center, Koror, PW96940, Palau

Background
It has been clearly shown that global warming and ocean acidification that result from the increase in atmospheric CO2 will affect a wide range of marine organisms and it is now threatening the whole ocean ecosystem. However, several gaps still remain in our knowledge for better predict and address impacts of climate change to the ocean: 1. Synergistic impacts of high temperature and low pH on marine organisms, 2. Impacts in the field, 3. Impacts at community level, and 4. Possible acclimation and adaptation responses to the high-CO2 world. In this presentation we will introduce studies conducted at coral reefs in Nikko Bay, located in the rock islands of Palau, western Pacific. Nikko Bay is a unique site that provides us an opportunity to address the gaps in knowledge.
Methods
Nikko Bay is a highly sheltered bay with spatially heterogeneous seawater chemistry due to the complex topography and high water residence time. The seawater pH within the bay ranges from 7.6 to 8.1, aragonite saturation (Ω) from 1.8 to 3.6 and the average temperature from 28.5 to 32.0°C degrees. For the evaluation of the effect of pH/temperature at community level, we conducted benthic community surveys along the gradient of the seawater pH and temperature among sites. We also conducted coral (Porites cylindrica) transplantation experiment along this gradient. Lastly, low pH/ high temperature tank experiment using P. cylindrica collected from different sites was also performed.
Findings
We found that the coral communities living in the highest temperature and lowest pH site had the highest resistance to the high temperature and low pH. However, we also found that coral growth rate collected from all the sites increases when transplanted to higher pH condition or cultured under high pH seawater. These results first suggest potential adaptation capacity of corals to the high-CO2 world, albeit with limitation. In the presentation, we also discuss the possible variability of coral reef community responses to the climate change.
Conclusions
Nikko Bay offers a potential living laboratory for the evaluation of global warming and ocean acidification at community level and adaptation capacity of the organisms to the high CO2 world. Results suggest possible adaptation capacity of corals and we suggest the evaluation of climate change on reef community and marine ecosystems should be a next step.