Ocean acidification impacts spine integrity but not regenerative capacity of spines and tube feet in adult sea urchins

Increasing atmospheric carbon dioxide (CO2) has resulted in a change in seawater chemistry and lowering of pH, referred to as ocean acidification. Understanding how different organisms and processes respond to ocean acidification is vital to predict how marine ecosystems will be altered under future scenarios of continued environmental change. Regenerative processes involving biomineralization in marine calcifiers such as sea urchins are predicted to be especially vulnerable. In this study, the effect of ocean acidification on regeneration of external appendages (spines and tube feet) was investigated in the sea urchin Lytechinus variegatus exposed to ambient (546 µatm), intermediate (1027 µatm) and high (1841 µatm) partial pressure of CO2 (pCO2) for eight weeks. The rate of regeneration was maintained in spines and tube feet throughout two periods of amputation and regrowth under conditions of elevated pCO2. Increased expression of several biomineralization-related genes indicated molecular compensatory mechanisms; however, the structural integrity of both regenerating and homeostatic spines was compromised in high pCO2 conditions. Indicators of physiological fitness (righting response, growth rate, coelomocyte concentration and composition) were not affected by increasing pCO2, but compromised spine integrity is likely to have negative consequences for defence capabilities and therefore survival of these ecologically and economically important organisms.

大气中二氧化碳（CO₂）浓度升高，引发海水化学性质改变与pH值降低，该过程被称为海洋酸化（ocean acidification）。明确不同生物类群与生态过程对海洋酸化的响应机制，对于预测未来环境持续变化情景下海洋生态系统的演变趋势至关重要。海洋钙化生物（marine calcifiers）如海胆的生物矿化相关再生过程，被认为尤其易受海洋酸化胁迫。本研究以杂色海胆（Lytechinus variegatus）为实验材料，设置了环境对照（546 µatm）、中等（1027 µatm）与高浓度（1841 µatm）二氧化碳分压（pCO₂）三种处理条件，将受试个体暴露于上述环境中共8周，探究海洋酸化对其外部附肢（棘与管足）再生过程的影响。在升高的pCO₂条件下，经两次截肢与再生周期后，海胆的棘与管足再生速率均保持稳定。多种与生物矿化相关的基因表达上调，提示存在分子补偿机制；但在高pCO₂条件下，再生棘与稳态棘的结构完整性均遭到破坏。生理适合度相关指标（翻正反应、生长速率、体腔细胞浓度与组成）并未随pCO₂升高出现显著变化，但棘结构完整性受损可能会对这类兼具重要生态与经济价值的海胆的防御能力乃至生存产生负面影响。