Light intensity modulates the effect of thermal stress on giant clams and their symbiotic zooxanthellae
摘要
Gradual climate change and extreme marine heatwaves (MHWs) pose a serious threat to tropical marine ecosystems, endangering the fisheries and aquaculture resources they support. A better understanding of species physiological responses to climate change-related stressors can help anticipate the risks and develop adaptive management strategies. While temperature is the main driver pushing organisms away from their optimal physiological and ecological performance, thermal stress is modulated by additional stressors in the wild, which cumulatively determine the extent of the impacts observed in nature. In this study we explored individual-level mechanisms driving the sensitivity of a symbiotic organism—the giant clam Tridacna maxima—to a range of temperatures (24, 27, 29, and 31 °C) and light intensities (150 and 1000 µmol m−2 s−1). After 18 days of exposure, we characterized the physiological response of both the symbiotic microalgae and the animal host using PAM fluorometry, respirometry, weight measurements, chlorophyll-a quantification, and measurements of zooxanthellae density and size. Our data revealed the crucial role of light in modulating the sensitivity of giant clams to warming. The effect of light and its interaction with temperature were stronger than temperature alone in driving responses of both the zooxanthellae (photosynthetic performance, zooxanthellae density and size, and oxygen production) and the host (respiration rate and condition index). By explicitly considering the interplay between temperature and light in photo-autotrophic organisms, aquaculture and fishery managers might have a tool for minimizing the impacts of climate change and MHW events on their activities.