Long-term isolation and local adaptation in Palau’s Nikko Bay help corals thrive in acidic waters
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The reefs in Palau’s Nikko Bay live in seawater with low pH that is similar to conditions predicted for 2100 because of ocean acidification. Nevertheless, the reefs at Nikko Bay have high coral cover and high diversity. We hypothesize that the low-pH environment in Nikko Bay is caused by low flushing rates, which causes long-term isolation and local adaptation. To test this hypothesis, we modeled the water circulation in and around Nikko Bay. Model results show that average residence time is 71 d, which is ten times the residence time on fore-reef habitats. The long residence time restricts the exchange of coral larvae in the bay with adjacent reefs, allowing persistent selection for tolerant traits and local adaptation. The corals in Nikko Bay are also more susceptible to local pollution because the waters are poorly flushed. Therefore, local management must focus on minimizing human impacts such as dredging, overfishing and pollution in the bay, which would compromise the condition of the corals that have already adapted to low-pH conditions.
KeywordsOcean acidification Coral reefs Flushing Residence time Resilience Adaptation
Authors would like to thank everyone involved with Palau International Coral Reef Center’s long-term coral reef monitoring program. We thank A. Merep for his assistance in the field. We also thank Y. S. Yuen and T. Kawai for their assistance with the current measurements. We are thankful to C. Doropoulos for reviewing an earlier version of this manuscript. This study was supported by NOAA Coral Reef Conservation Program, NOAA Coastal Oceans Program, Pew Fellowship in Marine Conservation, and JICA-JST.
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