As the global ocean continues to experience the consequences of an increase in the frequency and intensity of heat waves, the trend is expected to persist into the 21st century, with a projected tripling of heat waves by 2040. This phenomenon poses a significant threat to marine ecosystems and the survival of marine organisms, including the ecologically and economically vital bivalves. Bivalves are vulnerable to harm from heat stress at various levels of biological organization, and their growth can be negatively impacted by high temperatures, potentially leading to mass mortalities and posing a threat to ecosystem quality and food security. In light of these concerns, this review aims to provide a comprehensive examination of the effects of heat stress on bivalves. It summarizes the physiological and biochemical changes that bivalves undergo in response to extreme heat events and offers an overview of the strategies they employ to mitigate their impacts. A better understanding of the underlying mechanisms of bivalve responses to heat stress is crucial in order to fully appreciate the impact of these events on these organisms. This review synthesizes the current knowledge on heat stress in bivalves and highlights the importance of further research in this area. By providing a comprehensive overview of the physiological and biochemical changes that bivalves experience during heat stress and the strategies they use to mitigate its impact, this review aims to support the development of more effective approaches to minimize heat stress in bivalves.
Marine heatwaves (MHWs) can severely affect bivalves and ecosystems they support. Heat shock proteins (HSPs) are a group of molecular chaperones playing a critical role in the cellular protection and thermo tolerance and thereby constraining physiological responses of marine bivalves to MHWs. Here, we cloned the full-length of HSP70 cDNA from the Pinctada maximal (PmHSP70) and evaluated the expression of PmHSP70 in pearl oysters under acute and repeatedly occurring MHWs conditions. The full-length of PmHSP70 is 2,474 bp, containing an ORF of 1,956 bp encoding 655 amino acids with a predicted molecular weight of 71.23 kDa and 5.26 theoretical isoelectric point. Under the scenario of acute MHWs, the expression of PmHSP70 was significantly highly expressed at 32 and 36°C, and reached the highest at 12 and 72 h, respectively, indicating that pearl oysters rapidly up-regulated the expression of HSP70 in response to MHWs. In the repeatedly occurring MHWs scenario, the thermal response of pearl oysters was alleviated, as best exemplified by significantly lowered expression levels of PmHSP70. Therefore, we speculate that long-term and repeated MHWs can alleviate the thermal stress of pearl oysters. This finding is encouraging and will provide us with meaningful insights into the acclimation of marine bivalves to extreme environments in the future.
Many species, particularly marine organisms, are becoming more vulnerable to marine heatwaves due to climate change. Marine species anticipate perishing during marine heatwaves, but there is a growing interest in learning why some can resist. Using Pinctada maxima as a model species, we were able to clone a full-length cDNA encoding HSP90 with a calculated open reading frame of 2031 residues of amino acids and a molecular mass estimate of 78.08 kD to understand better the effects of marine heatwaves on the HSP90 gene expression in pearl oysters. The sequence of amino acids in P. maxima HSP90 was quite similar to the HSP90 families of Pinctada fucata martensii. At 32°C and 36°C, the expression of PmHSP90 significantly expressed and reached its highest level at 6 h, implying that in pearl oysters’ response to acute marine heatwaves, HSP90 expression rapidly increased. Pearl oysters’ temperature response was relieved, as best demonstrated by the dramatically reduced expression levels of PmHSP90 in the frequently reoccurring marine heatwaves event. Using these findings, it is possible to predict acute and repeated marine heatwaves in pearl oysters using P. maxima HSP90 as a molecular biomarker.
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