Highlights
- •Palau’s reef has a long-term naturally acidified inshore seawater (pH ~ 7.85).
- •Porites corals up-regulate calcifying fluid pH (~8.41) at normal- and low-pH sites.
- •Porites corals adapt calcifying fluid chemistry to long-term low-pH conditions.
- •Porites shows 15 % lower skeletal density under low-pH (~7.85) vs. open-ocean (~8.03).
Abstract
Ongoing ocean acidification is known to be a major threat to tropical coral reefs. To date, only few studies have evaluated the impacts of natural long-term exposure to low-pH seawater on the chemical regulation and growth of reef-building corals. This work investigated the different responses of the massive Porites coral living at normal (pHsw ~ 8.03) and naturally low-pH (pHsw ~ 7.85) seawater conditions at Palau over the last decades. Our results show that both Porites colonies maintained similar carbonate properties (pHcf, [CO32−]cf, DICcf, and Ωcf) within their calcifying fluid since 1972. However, the Porites skeleton of the more acidified conditions revealed a significantly lower density (~ 1.21 ± 0.09 g·cm−3) than the skeleton from the open-ocean site (~ 1.41 ± 0.07 g·cm−3). Overall, both Porites colonies exerted a strong biological control to maintain stable calcifying fluid carbonate chemistry that favored the calcification process, especially under low-pH conditions. However, the decline in skeletal density observed at low pH provides critical insights into Porites vulnerability to future global change.
Canesi M., Douville E., Bordier L., Dapoigny A., Coulibaly G. E., Montagna P., Béraud E., Allemand D., Planes S., Furla P., Gilson E., Roberty S., Zoccola D. & Reynaud S., 2024. Porites’ coral calcifying fluid chemistry regulation under normal- and low-pH seawater conditions in Palau Archipelago: impacts on growth properties. Science of the Total Environment 911: 168552. doi: 10.1016/j.scitotenv.2023.168552. Article.
