Acute heat-stress testing in coral bleaching research: a review of research using the Coral Bleaching Automated...

As climate change intensifies, identifying heat-resistant corals is essential for advancing coral-bleaching research and informing reef conservation and restoration. The Coral Bleaching Automated Stress System (CBASS) is designed to meet this need by conducting acute heat-stress assays within a standardized methodological framework. Given its affordability and short duration, CBASS use has increased since 2020, warranting a first review of its application. Here, we assess (1) the scope of CBASS research including geographic and species representation, (2) variation in experimental design, (3) the range of measured response variables, and (4) how CBASS-derived heat responses compare with those from longer-duration experiments and in situ surveys. We then synthesize these findings to identify advantages and limitations and suggest improvements. We show that CBASS studies exhibit taxonomic and depth biases similar to other coral-bleaching experiments. Most studies include adequate biological replication but insufficient tank replication. Temperature treatments were highly standardized, whereas rationales for selecting light levels were lacking. Frequent tissue sloughing and mortality in the highest temperature treatment underscore the need to re-evaluate the use of extreme temperatures. Chlorophyll fluorescence and associated dose-response metrics such as ED50 were the most commonly measured response variables, but standardization and reporting warrant improvement. Notably, in-depth review of the few studies comparing acute and longer-duration stress assays indicates that it remains unresolved whether CBASS-derived coral responses reliably predict coral performance under real-world heatwave scenarios. Consequently, we caution relying solely on acute stress assays to inform reef conservation and genotype selection for restoration planning until further validation is achieved.

The online version contains supplementary material available at 10.1007/s00338-026-02862-7.