CO2-induced ocean acidification increases anxiety in Rockfish via alteration of GABAA receptor functioning@en

The average surface pH of the ocean is dropping at a rapid rate due to the dissolution of anthropogenic CO2, raising concerns for marine life. Additionally, some coastal areas periodically experience upwelling of CO2-enriched water with reduced pH. Previous research has demonstrated ocean acidification (OA)-induced changes in behavioural and sensory systems including olfaction, which is due to altered function of neural gamma-aminobutyric acid type A (GABAA) receptors. Here, we used a camera-based tracking software system to examine whether OA-dependent changes in GABAA receptors affect anxiety in juvenile Californian rockfish (Sebastes diploproa). Anxiety was estimated using behavioural tests that measure light/dark preference (scototaxis) and proximity to an object. After one week in OA conditions projected for the next century in the California shore (1125 ± 100 µatm, pH 7.75), anxiety was significantly increased relative to controls (483 ± 40 µatm CO2, pH 8.1). The GABAA-receptor agonist muscimol, but not the antagonist gabazine, caused a significant increase in anxiety consistent with altered Cl- flux in OA-exposed fish. OA-exposed fish remained more anxious even after 7 days back in control seawater; however, they resumed their normal behaviour by day 12. These results show that OA could severely alter rockfish behaviour; however, this effect is reversible.由于人为源二氧化碳（anthropogenic CO₂）的溶解，海洋表层平均pH值正快速下降，引发了学界对海洋生物生存现状的广泛担忧。此外，部分沿海区域会周期性出现富含二氧化碳且pH值偏低的海水上升流。既往研究已证实，海洋酸化（Ocean Acidification, OA）可改变包括嗅觉在内的行为与感知系统，该效应源于神经γ-氨基丁酸A型（gamma-aminobutyric acid type A, GABAA）受体的功能异常。本研究采用基于摄像头的追踪软件系统，探究了海洋酸化诱导的GABAA受体变化是否会影响幼年加州岩鱼（Sebastes diploproa）的焦虑状态。焦虑程度通过两项行为学实验进行评估：一是测量明暗偏好（趋暗习性，scototaxis），二是评估物体趋近行为。将幼鱼置于模拟加州沿岸未来百年环境的酸化条件（1125 ± 100 µatm，pH 7.75）中饲养一周后，其焦虑程度相较于对照组（483 ± 40 µatm CO₂，pH 8.1）显著升高。GABAA受体激动剂蝇蕈醇（muscimol）而非拮抗剂加巴嗪（gabazine），可使酸化暴露组幼鱼的焦虑程度显著升高，这一结果与酸化暴露鱼类的氯离子通量异常现象相符。即便在转回对照海水环境饲养7天后，酸化暴露组幼鱼仍维持更高的焦虑水平；但至第12天时，其行为已恢复正常。上述结果表明，海洋酸化可能会严重改变岩鱼的行为模式，但该影响是可逆的。