Adaptive Responses of the Sea Anemone to the Interaction of Acidification and Global Warming.

Ocean acidification and warming are two of the most important threats to the existence of marine organisms and are predicted to co-occur in oceans. The present work evaluated the effects of acidification (AC: 24 ± 0.1 °C and 900 μatm CO), warming (WC: 30 ± 0.1 °C and 450 μatm CO), and their combination (CC: 30 ± 0.1 °C and 900 μatm CO) on the sea anemone, , from the aspects of photosynthetic apparatus (maximum quantum yield of photosystem II (PS II), chlorophyll level, and Symbiodiniaceae density) and sterol metabolism (cholesterol content and total sterol content). In a 15-day experiment, acidification alone had no apparent effect on the photosynthetic apparatus, but did affect sterol levels. Upregulation of their chlorophyll level is an important strategy for symbionts to adapt to high partial pressure of CO (CO) However, after warming stress, the benefits of high CO had little effect on stress tolerance in . Indeed, thermal stress was the dominant driver of the deteriorating health of . Cholesterol and total sterol contents were significantly affected by all three stress conditions, although there was no significant change in the AC group on day 3. Thus, cholesterol or sterol levels could be used as important indicators to evaluate the impact of climate change on cnidarians. Our findings suggest that might be relatively insensitive to the impact of ocean acidification, whereas increased temperature in the future ocean might impair viability of .