466 / 2024-09-17 17:41:50
Eco-Physiological Response of Macroalgae to Ocean Acidification: Results from an In-situ CO2 Seep
CO2 seep,Macroalgae,Ocean acidification,Photosynthesis,Photoinhibition
Session 9 - Global Ocean Changes: Regional Processes and Ecological Impacts
Abstract Accepted
To investigate the effects of ocean acidification (OA) on macroalgae, we have performed in-situ experiments around CO2 seep in Shimoda, Japan, during the period of June to July in 2019. A total 23 species of macroalgae were observed in control site (pH=8.27), including 2 species of green algae, 18 species of red algae and 3 species of brown algae, while in the near of CO2 seep area (pH=7.9), only 10 species of macroalgae were observed, referring to 3 species of green algae, 4 species of red algae and 3 species of brown algae. With decrease of the density of macroalgae, our results implied that the increase of CO2 (lower pH) significantly reduce the diversity and abundance of macroalgae. By using a GFS-3000 gas exchange system, the carbon assimilation rate of those tested macroalgae were identified to increase from control site to CO2 seep area, while the K0.5 (half saturation constant of CO2) showed a significant decrease, suggesting that high CO2 induced OA increased the carbon fixation of macroalgae but declined the activity of CO2-concentrating mechanisms (CCMs). The further measurements of rapid light curves by a Dual-wavelength pulse-amplitude modulated Chlorophyll a fluorescence monitoring system showed that those macroalgae inhabited in control site exhibited a higher electron transport rate, a higher light utilization efficiency and a lower minimal saturating light intensity, compared with those macroalgae living in CO2 seep area. Thus, we speculated that OA may modulate the effects of light fluctuations on macroalgae. To further verify this speculation, light-sensitivity of Gelidium elegans and Dictyopteris undulata, the dominated species around control site and CO2 seep area, respectively, were analyzed. Results showed that OA significantly increased the photosystem II (PSII) damage rate of G. elegans, but decreased its repair rate during the high light treatment; D. undulata, inhabited in the CO2 seep area (low pH), was not affected by high light. In conclusion, our present results demonstrate that effects of OA on macroalgae are species-specific.