摘要：Contemporary cnidarian-algae symbioses are challenged by increasing CO2 concentrations (ocean warming and acidification) affecting organisms' biological performance. We examined the natural variability of carbon and nitrogen isotopes in the symbiotic sea anemone Anemonia viridis to investigate dietary shifts (autotrophy/heterotrophy) along a natural p CO2 gradient at the island of Vulcano, Italy. δ13C values for both algal symbionts ( Symbiodinium ) and host tissue of A. viridis became significantly lighter with increasing seawater p CO2. Together with a decrease in the difference between δ13C values of both fractions at the higher p CO2 sites, these results indicate there is a greater net autotrophic input to the A. viridis carbon budget under high p CO2 conditions. δ15N values and C/N ratios did not change in Symbiodinium and host tissue along the p CO2 gradient. Additional physiological parameters revealed anemone protein and Symbiodinium chlorophyll a remained unaltered among sites. Symbiodinium density was similar among sites yet their mitotic index increased in anemones under elevated p CO2. Overall, our findings show that A. viridis is characterized by a higher autotrophic/heterotrophic ratio as p CO2 increases. The unique trophic flexibility of this species may give it a competitive advantage and enable its potential acclimation and ecological success in the future under increased ocean acidification.
