Coral reefs are biodiversity hotspots that support fisheries, protect coastlines, and sustain millions of people. Their survival depends strongly on the symbiosis between reef-building corals and microscopic algae in the family Symbiodiniaceae. Under thermal stress, corals may lose these symbionts, leading to coral bleaching. However, not all Symbiodiniaceae lineages respond to heat in the same way. Some are associated with higher thermal tolerance and may improve coral performance under warming conditions. Therefore, understanding how coral symbiont communities are associated with environmental availability and host identity is important for predicting coral resilience under climate change.
Many studies have examined how coral-associated Symbiodiniaceae communities respond to local heat stress, but less is known about how environmental Symbiodiniaceae availability changes across broad natural temperature gradients. This project will investigate coral-associated and environmental Symbiodiniaceae communities across a subtropical-to-tropical latitudinal gradient in the Northwestern Pacific, including coastal and island regions from Jeju and Okinawa to Taiwan, Hong Kong, Hainan, and the Philippines. These regions span strong differences in mean sea surface temperature and provide a useful natural system for examining how thermal regime is associated with Symbiodiniaceae distributions.
I hypothesize that the same coral species will show similar Symbiodiniaceae composition across different regions, but that the relative abundance and distribution of these symbionts will vary along latitude in relation to local environmental conditions. In other words, widely distributed coral species may retain a shared set of core Symbiodiniaceae lineages across sites, reflecting host-associated consistency, while also showing regional shifts in symbiont community structure that correspond to changes in the surrounding environmental symbiont pool. 
This study will provide a broad survey of coral-associated and environmental Symbiodiniaceae communities across a latitudinal thermal gradient in the Northwestern Pacific. By characterizing Symbiodiniaceae composition within widely distributed coral species and in nearby environmental samples, this project will document how symbiont communities vary across regions and how these patterns correspond to latitude, thermal conditions, and local environmental symbiont availability. This wide-range comparison will provide baseline information on regional variation of coral–Symbiodiniaceae associations. The results will help identify whether some coral species maintain shared symbiont lineages across distant regions, whether local environmental pools are associated with regional differences in coral symbiont composition, and where thermally tolerant Symbiodiniaceae lineages are more commonly found.