Response of zooxanthellate scleractinian corals to elevation of seawater temperature during summer in a temperate Japanese coastal sea (Takashima, Japan)

Abstract In contrast to tropical and subtropical regions, where coral abundance is declining due to elevated summer seawater temperatures, expansions of coral ranges have been reported in temperate Japanese regions due to an increase in seawater temperature. However, the vulnerability of corals in temperate Japanese regions to elevated summer seawater temperatures is not well known. In this study, we assessed the bleaching state of corals with elevated seawater temperatures during summer in a temperate Japanese coastal sea around Takashima Island, using an underwear color reference card (Coral Health Chart). This study showed that the color of temperate corals turned pale with increasing seawater temperature during summer. However, the corals did not reach a bleached state. Approaching a typhoon may contribute to maintenance of coral health at Takashima Beach by mitigating high seawater temperatures during summer and preventing the accumulation of thermal stress in corals.