The Xiamen Symposium on Marine Environmental Sciences (XMAS 2027)

High-latitude coral communities are increasingly regarded as potential refugia under global ocean warming. However, the ecological stability of these marginal coral ecosystems may be strongly constrained by extreme cold events, especially marine cold spells that exceed the physiological tolerance of tropical and subtropical coral species. Here, we focus on the Dongshan coral community in the Taiwan Strait, one of the northernmost coral distribution areas along the Chinese coast, to investigate the impacts and mechanisms of extreme cold spells on representative coral species’ distribution, physiology, and biogeography.

Since the 1980s, winter marine cold spells in the Taiwan Strait have shown increasing frequency and intensity. During December 2024 to March 2025, an exceptionally strong cold spell occurred, with seawater temperatures 2–4 °C below the winter climatology and cold-stress conditions lasting for more than 85 days in the Dongshan coral habitat. By combining continuous underwater field monitoring before, during, and after the cold event with controlled low-temperature experiments, physiological measurements, molecular analyses, and biogeographic assessments, this study evaluates species-specific responses of representative corals, including Oulastrea crispata, Cyphastrea serailia, and Duncanopsammia peltata.

Our observations documented the full process of cold bleaching in a high-latitude coral community, including changes in bleaching severity, mortality, and post-event recovery. Physiological analyses focused on photosynthetic performance, symbiont density, chlorophyll content, oxidative stress, antioxidant enzyme activity, and energy reserves. In parallel, host genomic resources, microsatellite markers, Symbiodiniaceae profiling, and bacterial community analyses were used to explore the roles of genetic differentiation, symbiont shuffling, and microbiome restructuring in cold tolerance and resilience. Preliminary evidence suggests that low temperature, together with geographic distance, may contribute to population differentiation, while relatively stable microbial core communities may partially compensate for cold-induced symbiont instability.

These findings indicate that marine cold spells can reshape the physiological performance, community structure, and potential distribution limits of high-latitude corals. Although poleward coral expansion is often interpreted as a sign of future climate refugia, recurrent extreme cold events may instead create “climate traps”, where warming-driven distributional opportunities are offset by episodic cold-induced mortality. This study provides new evidence for understanding coral biogeographic limits under climate extremes and offers scientific support for early warning, conservation, and adaptive management of marginal coral ecosystems.