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<p>This study examined early-stage recovery of the colorful outer mantle in <i>Tridacna squamosa</i> over 11&#xa0;days at 26&#xa0;°C following partial thermal bleaching at 31&#xa0;°C. Recovery of symbiotic dinoflagellates was assessed through mantle coloration, symbiont density, transcript and protein levels of form II ribulose-1,5-bisphosphate carboxylase/oxygenase (Zoox-RBCII), and concentrations of total chlorophyll and peridinin. Host recovery was evaluated via iridocyte abundance and spatial organization using immunofluorescence microscopy with vacuolar H⁺-ATPase subunit A (ATP6V1A) as a marker and a novel quantification scheme. Restorations of transcript and protein levels of ATP6V1A and carbonic anhydrase 2-like (CA2), key enzymes in the host carbon concentrating mechanism (CCM), were also examined. Partial recovery occurred in giant clams returned to plain seawater at 26&#xa0;°C, whereas NH<sub>4</sub><sup>+</sup> and PO<sub>4</sub><sup>3−</sup> supplementation substantially accelerated restoration across nearly all recovery metrics. Supplemented symbionts rapidly regained carbon fixation capacity, as increases in Zoox-RBCII protein abundance preceded rises in symbiont density. Notably, proliferation and reorganization of iridocytes essential for photosynthesis were evident as early as day 1 of recovery, with or without nutrient supplementation. Moreover, supplementation enhanced restoration of host ATP6V1A and CA2 protein abundances to levels exceeding pre-bleaching values on day 5 and 11, underscoring the pivotal role of the host CCM in supporting symbiont functional recovery. Overall, successful restoration of the <i>T. squamosa</i>–dinoflagellate bidirectional nutrient exchange depends on coordinated recovery of host photo-physiological system and symbiont photosynthesis, aided by sufficient nitrogen and phosphorus. Hence, inorganic nutrient supplementation may help mitigate thermal bleaching impacts on Indo-Pacific giant clams.</p>

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Ammonium and phosphate supplementation accelerates post-bleaching recovery in the fluted giant clam (Tridacna squamosa): evidence for host-mediated thermal resilience

  • 期刊论文

  • 发表日期：

    2026年7月4日

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

摘要

This study examined early-stage recovery of the colorful outer mantle in Tridacna squamosa over 11 days at 26 °C following partial thermal bleaching at 31 °C. Recovery of symbiotic dinoflagellates was assessed through mantle coloration, symbiont density, transcript and protein levels of form II ribulose-1,5-bisphosphate carboxylase/oxygenase (Zoox-RBCII), and concentrations of total chlorophyll and peridinin. Host recovery was evaluated via iridocyte abundance and spatial organization using immunofluorescence microscopy with vacuolar H⁺-ATPase subunit A (ATP6V1A) as a marker and a novel quantification scheme. Restorations of transcript and protein levels of ATP6V1A and carbonic anhydrase 2-like (CA2), key enzymes in the host carbon concentrating mechanism (CCM), were also examined. Partial recovery occurred in giant clams returned to plain seawater at 26 °C, whereas NH4+ and PO43− supplementation substantially accelerated restoration across nearly all recovery metrics. Supplemented symbionts rapidly regained carbon fixation capacity, as increases in Zoox-RBCII protein abundance preceded rises in symbiont density. Notably, proliferation and reorganization of iridocytes essential for photosynthesis were evident as early as day 1 of recovery, with or without nutrient supplementation. Moreover, supplementation enhanced restoration of host ATP6V1A and CA2 protein abundances to levels exceeding pre-bleaching values on day 5 and 11, underscoring the pivotal role of the host CCM in supporting symbiont functional recovery. Overall, successful restoration of the T. squamosa–dinoflagellate bidirectional nutrient exchange depends on coordinated recovery of host photo-physiological system and symbiont photosynthesis, aided by sufficient nitrogen and phosphorus. Hence, inorganic nutrient supplementation may help mitigate thermal bleaching impacts on Indo-Pacific giant clams.