Anemone abundance and productivity at North Vulcano Island in May 2011

Increased seawater pCO2, and in turn 'ocean acidification' (OA), is predicted to profoundly impact marine ecosystem diversity and function this century. Much research has already focussed on calcifying reef-forming corals (Class: Anthozoa) that appear particularly susceptible to OA via reduced net calcification. However, here we show that OA-like conditions can simultaneously enhance the ecological success of non-calcifying anthozoans, which not only play key ecological and biogeochemical roles in present day benthic ecosystems but also represent a model organism should calcifying anthozoans exist as less calcified (soft-bodied) forms in future oceans. Increased growth (abundance and size) of the sea anemone (Anemonia viridis) population was observed along a natural CO2 gradient at Vulcano, Italy. Both gross photosynthesis (PG) and respiration (R) increased with pCO2 indicating that the increased growth was, at least in part, fuelled by bottom up (CO2 stimulation) of metabolism. The increase of PG outweighed that of R and the genetic identity of the symbiotic microalgae (Symbiodinium spp.) remained unchanged (type A19) suggesting proximity to the vent site relieved CO2 limitation of the anemones' symbiotic microalgal population. Our observations of enhanced productivity with pCO2, which are consistent with previous reports for some calcifying corals, convey an increase in fitness that may enable non-calcifying anthozoans to thrive in future environments, i.e. higher seawater pCO2. Understanding how CO2-enhanced productivity of non- (and less-) calcifying anthozoans applies more widely to tropical ecosystems is a priority where such organisms can dominate benthic ecosystems, in particular following localized anthropogenic stress.

本世纪内，海水二氧化碳分压（pCO₂）升高进而引发的‘海洋酸化（OA）’，预计将对海洋生态系统的多样性与功能产生深远影响。此前大量研究均聚焦于钙化造礁珊瑚（Anthozoa纲），这类生物因净钙化作用减弱，对海洋酸化表现出尤为显著的易感性。但本研究表明，类海洋酸化条件可同时提升非钙化珊瑚虫纲生物的生态竞争力。这类生物不仅在当代底栖生态系统中发挥关键的生态与生物地球化学功能，若未来海洋中钙化珊瑚虫纲生物退化为低钙化（软躯体）形式，它们还可作为模式生物开展相关研究。研究人员在意大利武尔卡诺（Vulcano）的天然二氧化碳梯度海域中，观测到海葵（Anemonia viridis）种群的生长（包括丰度与个体大小）得到显著提升。总光合速率（PG）与呼吸速率（R）均随pCO₂升高而增强，表明种群生长的提升至少部分源于二氧化碳刺激代谢的自下而上调控效应。总光合速率的增幅超过呼吸速率，且共生微藻（Symbiodinium属）的遗传特征未发生改变（类型为A19），这表明靠近海底喷口的海域缓解了海葵共生微藻种群的二氧化碳限制。本研究观测到的、随pCO₂升高而增强的生产力与此前部分钙化珊瑚的相关研究结果一致，这表明非钙化珊瑚虫纲生物的适合度得到提升，使其可在未来高海水pCO₂的环境中繁盛生长。探明非（及低）钙化珊瑚虫纲生物的CO₂增强型生产力效应能否在热带生态系统中更广泛地推广应用，是当前的优先研究方向——这类生物可在这类生态系统中占据主导地位，尤其是在遭受局部人为胁迫时。