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<p>Rising ocean temperatures trigger bleaching in dinoflagellate-bearing reef animals, including giant clams. In this study, giant clams (<i>Tridacna squamosa</i>) were kept at 26&#xa0;°C (control) or exposed to 31&#xa0;°C for a maximum of 57&#xa0;days to evaluate whether symbionts and host cells in the colorful outer mantle could acclimate to temperature stress in accordance with the oxidative stress theory of bleaching. Elevated temperature led to partial bleaching of the outer mantle, leaving behind ∼&#xa0;36% of the symbiont population that appeared acclimated. Such partial loss of symbionts could be a survival strategy to limit excessive reactive oxygen species (ROS) generation by reducing the total symbiont population. The surviving symbionts had a reduced carbon-fixing capacity with substantially less form II ribulose-1,5-bisphosphate carboxylase/oxygenase protein. However, chlorophyll and peridinin contents increased&#xa0;∼&#xa0;twofold in these symbionts, presumably forming more peridinin–chlorophyll-<i>a</i>–protein that could act as an antioxidant inside the plastids. Notably, temperature stress altered the spatial organization of iridocytes in relation to the residual symbionts in the outer mantle. This unique host response could minimize the irradiance received by the residual symbionts, thereby suppressing ROS production during illumination. Furthermore, the host upregulated transiently the protein expression of copper-zinc superoxide dismutase in the outer mantle to combat oxidative stress. Overall, our results provide new insights into the resilience of giant clams to temperature-induced bleaching and denote the importance of coordinated antioxidant strategies of both host and symbionts in promoting holobiont survival.</p>

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Partial bleaching and survival responses in the outer mantle of the giant clam Tridacna squamosa exposed to temperature stress

  • 期刊论文

  • 发表日期：

    2025年10月9日

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  • Caryn Z. Pang,
  • Yuen K. Ip,
  • Shit F. Chew

摘要

Rising ocean temperatures trigger bleaching in dinoflagellate-bearing reef animals, including giant clams. In this study, giant clams (Tridacna squamosa) were kept at 26 °C (control) or exposed to 31 °C for a maximum of 57 days to evaluate whether symbionts and host cells in the colorful outer mantle could acclimate to temperature stress in accordance with the oxidative stress theory of bleaching. Elevated temperature led to partial bleaching of the outer mantle, leaving behind ∼ 36% of the symbiont population that appeared acclimated. Such partial loss of symbionts could be a survival strategy to limit excessive reactive oxygen species (ROS) generation by reducing the total symbiont population. The surviving symbionts had a reduced carbon-fixing capacity with substantially less form II ribulose-1,5-bisphosphate carboxylase/oxygenase protein. However, chlorophyll and peridinin contents increased ∼ twofold in these symbionts, presumably forming more peridinin–chlorophyll-a–protein that could act as an antioxidant inside the plastids. Notably, temperature stress altered the spatial organization of iridocytes in relation to the residual symbionts in the outer mantle. This unique host response could minimize the irradiance received by the residual symbionts, thereby suppressing ROS production during illumination. Furthermore, the host upregulated transiently the protein expression of copper-zinc superoxide dismutase in the outer mantle to combat oxidative stress. Overall, our results provide new insights into the resilience of giant clams to temperature-induced bleaching and denote the importance of coordinated antioxidant strategies of both host and symbionts in promoting holobiont survival.