Gradual climate change and extreme marine heatwaves (MHWs) pose a serious threat to tropical marine ecosystems, endangering the fisheries and aquaculture resources they support. Effective adaptive management and the development of mitigation strategies depend on accurate predictions of the potential impacts of frequent and intense elevated temperature events on the productivity of these vital resources. A deeper understanding of species physiological responses to climate change-related stressors can help anticipate the risks. In this study, we explore mechanisms driving the sensitivity of the giant clam T. maxima to elevated temperature, providing insights that can aid in mitigating the effects of MHW on giant clam fisheries and aquaculture.
To investigate the effects of temperature and light intensity on the physiological condition of T. maxima, we conducted laboratory experiments at the Pacific Centre of Ifremer in Tahiti. Giant clams (n = 192; mean shell length= 6.5 ± 0.5 cm) from Reao lagoon (Tuamotu Archipelago) were exposed to eight experimental treatments combining four temperature levels (24°C, 27°C, 29°C, and 31°C) and two light intensities (150 and 1000 µmol s-1 m-2). After 18 days of exposure we used PAM fluorometry, respirometry, and measurements of zooxanthellae density (Chl-a and cell count) to characterize the physiological responses of both the symbiotic microalgae and animal hosts.
Our key findings emphasize the crucial role of light in determining the sensitivity of giant clam to warming. The effects of light and its interaction with temperature were stronger than temperature alone for several measured responses, including the photosynthetic yield of zooxanthellae (Figure 1A) and the respiration rate of giant clams (Figure 1B). These findings open up new opportunities for aquaculture and fishery management to minimize the impact of future MHWs.