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Marine biologists studying coral reefs off the coast of a volcanic archipelago have documented an unexpected pattern of thermal resilience in certain coral colonies that survived a severe bleaching event five years ago while neighboring colonies of the same species died. Bleaching occurs when unusually warm water causes corals to expel the symbiotic algae living in their tissues, often leading to starvation and death if temperatures do not recede quickly. In this study, researchers collected tissue samples from 340 surviving colonies and compared their algal symbionts against samples taken from colonies that did not survive the same warming event. They found that the survivors hosted a measurably higher proportion of a heat-tolerant algal strain, one that had previously been considered rare and functionally marginal in that reef system. Genetic analysis suggested that some surviving colonies had likely harbored small background populations of this heat-tolerant strain even before the bleaching event, allowing them to shift their symbiont composition rapidly once the more heat-sensitive algae were expelled. The researchers caution that this adaptive flexibility, while promising, is not a guarantee of long-term reef survival under continued warming. Colonies that hosted the heat-tolerant strain grew markedly more slowly than unaffected colonies during the two years following the bleaching event, indicating a possible trade-off between thermal resilience and overall reef productivity. The study's lead author noted that reefs dominated by heat-tolerant but slow-growing coral may become structurally weaker over time, offering less habitat complexity for fish and invertebrate species that depend on reef architecture. The team is now investigating whether selectively encouraging the heat-tolerant strain in reef restoration projects could help some reefs persist through future warming events, while acknowledging that such interventions would need to be weighed against the ecological costs of reduced growth rates.