Marine heatwaves (MHWs) have occurred with increasing duration, frequency and intensity in the past decade in the South China Sea, posing serious threats to marine ecosystems and fisheries. However, the impact of MHWs on marine bivalves – one of the most ecologically and economically important fauna in coastal ecosystems – remains largely unknown. Here, we investigated physiological responses of the pearl oyster, Pinctada maxima inhabiting a newly identified climate change hotspot (Beibu Gulf, South China Sea) to short-lasting and repeatedly-occurring MHWs scenarios. Following 3-day exposure to short-lasting MHWs scenarios with water temperature rapidly arising from 24 °C to 28 °C, 32 °C and 36 °C, respectively, mortality rates of pearl oysters increased, and especially they suffered 100% mortality at 36 °C. Activities of enzymes including acid phosphatase (ACP), alkaline phosphatase (AKP), glutathione (GSH) and level of malondialdehyde (MDA) increased significantly with increasing intensity and duration of MHWs, indicating thermal stress responses. When exposed to repeatedly-occurring MHWs scenarios, mortality rates of pearl oysters increased slightly, and thermal stress responses were alleviated, as exemplified by significant decreases in ACP, AKP, GSH and MDA activities compared with those during short-lasting MHWs scenarios, demonstrating the potential of P. maxima to acclimate rapidly to MHWs. These findings advance our understanding of how marine bivalves respond to MHWs scenarios varying in duration, frequency, and intensity.

过去十年，南海发生的海洋热浪（MHWs）持续时间、频率和强度不断增加，对海洋生态系统和渔业构成严重威胁。然而，MHW 对海洋双壳类动物——沿海生态系统中最具生态和经济意义的动物群之一——的影响在很大程度上仍然未知。在这里，我们调查了珍珠贝 Pinctada maxima 的生理反应居住在新确定的气候变化热点（北部湾、南海）到短期和反复发生的 MHW 情景。在水温分别从 24°C 快速上升到 28°C、32°C 和 36°C 的短时 MHW 情景下暴露 3 天后，珍珠贝的死亡率增加，尤其是在36℃。酸性磷酸酶 (ACP)、碱性磷酸酶 (AKP)、谷胱甘肽 (GSH) 和丙二醛 (MDA) 等酶的活性随着 MHW 强度和持续时间的增加而显着增加，表明热应激反应。当暴露于重复发生的 MHW 情景时，珍珠贝的死亡率略有增加，热应激反应得到缓解，例如 ACP、AKP、P. maxima迅速适应 MHW。这些发现促进了我们对海洋双壳类动物如何对持续时间、频率和强度不同的 MHW 情景做出反应的理解。