Bioenergetic trade-offs in the sea cucumber Apostichopus japonicus (Echinodermata: Holothuroidea) in response to CO2-driven ocean acidification

Ocean acidification (OA) caused by excessive CO2 is a potential ecological threat to marine organisms. The impacts of OA on echinoderms are well-documented, but there has been a strong bias towards sea urchins, and limited information is available on sea cucumbers. This work examined the effect of medium-term (60 days) exposure to three pH levels (pH 8.06, 7.72, and 7.41, covering present and future pH variability) on the bioenergetic responses of the sea cucumber, Apostichopus japonicus, an ecologically and economically important holothurian in Asian coasts. Results showed that the measured specific growth rate linearly decreased with decreased pH, leading to a 0.42 %/day decrease at pH 7.41 compared with that at pH 8.06. The impacts of pH on physiological energetics were variable: measured energy consumption and defecation rates linearly decreased with decreased pH, whereas maintenance energy in calculated respiration and excretion were not significantly affected. No shift in energy allocation pattern was observed in A. japonicus upon exposure to pH 7.72 compared with pH 8.06. However, a significant shift in energy budget occurred upon exposure to pH 7.41, leading to decreased energy intake and increased percentage of energy that was lost in feces, thereby resulting in a significantly lowered allocation into somatic growth. These findings indicate that adult A. japonicus is resilient to the OA scenario at the end of the twenty-first century, but further acidification may negatively influence the grazing capability and growth, thereby influencing its ecological functioning as an "ecosystem engineer" and potentially harming its culture output.由过量二氧化碳导致的海洋酸化（Ocean Acidification, OA）是威胁海洋生物的潜在生态威胁。目前学界已对海洋酸化对棘皮动物的影响开展了较为充分的研究，但此类研究多偏向海胆类，针对海参的相关报道仍较为有限。本研究以亚洲沿海兼具生态与经济价值的重要海参纲物种——仿刺参（*Apostichopus japonicus*）为研究对象，探究了中期（60天）暴露于三种pH梯度（pH 8.06、7.72与7.41，覆盖当前及未来海洋pH变化范围）对其生物能量学响应的影响。实验结果显示，受试仿刺参的特定生长率随pH降低呈线性下降趋势：相较于pH 8.06组，pH 7.41组的特定生长率每日降低0.42%。pH对仿刺参的生理能量学影响存在差异：实测的能量消耗率与排粪率随pH降低呈线性下降趋势，但通过呼吸与排泄计算得到的维持能并未受到显著影响。相较于pH 8.06组，pH 7.72组的仿刺参能量分配模式未发生显著改变。但当暴露于pH 7.41环境时，仿刺参的能量收支出现了显著变化：其能量摄入减少，粪便中流失的能量占比升高，最终导致用于体组织生长的能量分配比例显著降低。上述研究结果表明，成年仿刺参对21世纪末的海洋酸化情景具备一定耐受性，但进一步的海洋酸化可能会对其摄食能力与生长产生负面影响，进而干扰其作为“生态系统工程师”的生态功能，并可能损害其养殖产量。