Potential local adaptation of corals at acidified and warmed Nikko Bay, Palau

Abstract

Ocean warming and acidification caused by increases of atmospheric carbon dioxide are now thought to be major threats to coral reefs on a global scale. Here we evaluated the environmental conditions and benthic community structures in semi-closed Nikko Bay at the inner reef area in Palau, which has high pCO2 and seawater temperature conditions with high zooxanthellate coral coverage. Nikko Bay is a highly sheltered system with organisms showing low connectivity with surrounding environments, making this bay a unique site for evaluating adaptation and acclimatization responses of organisms to warmed and acidified environments. Seawater pCO2/Ωarag showed strong gradation ranging from 380 to 982 µatm (Ωarag: 1.79–3.66), and benthic coverage, including soft corals and turf algae, changed along with Ωarag while hard coral coverage did not change. In contrast to previous studies, net calcification was maintained in Nikko Bay even under very low mean Ωarag (2.44). Reciprocal transplantation of the dominant coral Porites cylindrica showed that the calcification rate of corals from Nikko Bay did not change when transplanted to a reference site, while calcification of reference site corals decreased when transplanted to Nikko Bay. Corals transplanted out of their origin sites also showed the highest interactive respiration (R) and lower gross photosynthesis (Pg) to respiration (Pg:R), indicating higher energy acquirement of corals at their origin site. The results of this study give important insights about the potential local acclimatization and adaptation capacity of corals to different environmental conditions including pCO2 and temperature.

High Coral Recruitment Despite Coralline Algal Loss Under Extreme Environmental Conditions

“…Indeed, R2 is located in a "culde-sac" between two islets with sparse but abundant reefs. It is characterized by a fine sediment bottom, and a low seawater renewal rate, likely such as for the Rock Islands in Palau (Micronesia) (Barkley et al, 2015;Shamberger et al, 2018;Kurihara et al, 2021). The combined effect of biological activities and carbonate disequilibrium likely caused such low pH values which are frequent and typical for many coastal fringing reefs with limited seawater exchanges with the lagoon.…”

Genetic and physiological traits conferring tolerance to ocean acidification in mesophotic corals

“…For Cladocopium sp., evidence of greater capacity to deal with high pCO 2 conditions is scarce; however, some coral species that are adapted to naturally high pCO 2 environments have been shown to mainly harbor symbionts of the genus Cladocopium (Kurihara et al, 2021), suggesting that Cladocopium sp. may indeed possess a better capacity to thrive under high pCO 2 conditions.…”

Assessing the relative accuracy of coral heights reconstructed from drones and structure from motion photogrammetry on coral reefs

“…1a), a semi-enclosed bay characterized by a maze of shallowwater channels, separated by shallow sills emerging during spring low tides (Golbuu et al 2016). These reefs are of particular ecological value and scientific interest because of their unusually warm and acidic waters and counter-intuitively high coral coverage and diversity (Golbuu et al 2016;Kurihara et al 2021). They are also particularly amenable to UAS surveys because they are sheltered from the wind by steep rocky cliffs and have low hydrodynamic influence from the adjacent ocean (Golbuu et al 2016).…”