Seawater carbonate chemistry and metabolic rates, bloodbased metrics in newborn blacktip reef sharks

Anthropogenic ocean acidification (OA) is a threat to coral reef fishes, but few studies have investigated responses of high-trophic-level predators, including sharks. We tested the effects of 72-hr exposure to OA-relevant elevated partial pressures of carbon dioxide (pCO2) on oxygen uptake rates, acid–base status, and haematology of newborn tropical blacktip reef sharks (Carcharhinus melanopterus). Acute exposure to end-of-century pCO2 levels resulted in elevated haematocrit (i.e. stress or compensation of oxygen uptake rates) and blood lactate concentrations (i.e. prolonged recovery) in the newborns. Conversely, whole blood and mean corpuscular haemoglobin concentrations, blood pH, estimates of standard and maximum metabolic rates, and aerobic scope remained unaffected. Taken together, newborn blacktip reef sharks appear physiologically robust to end-of-century pCO2 levels, but less so than other, previously investigated, tropical carpet sharks. Our results suggest peak fluctuating pCO2 levels in coral reef lagoons could still physiologically affect newborn reef sharks, but studies assessing the effects of long-term exposure and in combination with other anthropogenic stressors are needed.

人为海洋酸化（Anthropogenic ocean acidification, OA）是珊瑚礁鱼类面临的威胁，但针对包括鲨鱼在内的高营养级捕食者响应的研究却较为匮乏。本研究测试了新生热带黑鳍礁鲨（Carcharhinus melanopterus）在72小时内暴露于与OA相关的高二氧化碳分压（partial pressure of carbon dioxide, pCO₂）环境下，其摄氧率、酸碱状态及血液学（haematology）指标的变化。急性暴露于本世纪末水平的pCO₂导致幼鲨红细胞压积（haematocrit，即摄氧率的应激反应或代偿）及血液乳酸浓度（即恢复时间延长）升高。反之，全血及平均红细胞血红蛋白浓度（mean corpuscular haemoglobin concentration）、血液pH值、标准代谢率与最大代谢率的估算值及有氧代谢范围均未受影响。综上，新生黑鳍礁鲨对本世纪末水平的pCO₂表现出一定的生理耐受性，但相较于此前研究的其他热带须鲨（tropical carpet sharks）则稍逊一筹。研究结果表明，珊瑚礁泻湖中的峰值波动pCO₂水平仍可能对新生礁鲨产生生理影响，但仍需开展长期暴露及与其他人为应激源联合作用的效应评估研究。