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A decline in macro-algae species resulting in the overwhelming prevalence of Corallina species is caused by low-pH seawater induced by short-term acid rain

Gao, Shan, Sun, Qinghai, Tao, Yueliang, Wang, Xulei, Li, Wei, Huan, Li, Wu, Mingjiang, Wang, Guangce
Journal of experimental marine biology and ecology 2016 v.475 pp. 144-153
Corallina, Ulva, acid deposition, air, calcium carbonate, carbon, carbon dioxide, dominant species, littoral zone, ocean acidification, pH, photosystem II, seawater, species diversity, thallus, China
The increase in atmospheric CO2 and acid rain precipitation are serious global environmental problems that have had worldwide consequences, including the damage of biodiversity in intertidal zones. The decline in species richness in the intertidal zone of Wenzhou, China, is a typical example. In this study, we investigated the effects of CO2-enriched seawater, CO2-enriched air and acid rain on a dominant species, Corallina sp., and an inferior species, Ulva conglobata, in the intertidal zone of Wenzhou. The responses of Corallina sp. and U. conglobata to high-CO2 seawater are similar, demonstrating that both of them are tolerant of seawater acidification induced by aerating CO2-enriched air. The PSII activities of Corallina sp. declined markedly when exposed to CO2-free air, while they increased significantly with high-CO2 air. An increase of non-photochemical quenching (NPQ) was induced by CO2-free air, but it declined remarkably with CO2-enriched air, suggesting that Corallina sp. can use atmospheric CO2 as carbon source for photosynthesis. Corallina sp. survived extremely low pH conditions (pH3) and could regulate the pH of their ambient seawater through the dissolution of CaCO3, while the photosynthetic properties of U. conglobata decreased drastically and even the thalli were damaged irreversibly under low pH conditions (pH3). These results suggest that Corallina sp. is much more tolerant of extremely low pH than U. conglobata. Based on these results, we suggest that it is not the increase of atmospheric CO2 but acid rain at least in part contributed to the damage of the biodiversity in the intertidal zone, with the result that these areas are now mainly dominated by Corallina sp.