Thermal refugia

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Locations where a local physical process holds reef temperature below the regional bleaching threshold during a marine heatwave: upwelling that pulls cool water onto the shelf, strong tidal mixing that prevents a warm surface layer from stratifying, deep water adjacent to the reef, or turbidity and cloud that cut the light dose. Refugia are the principal argument for spatial rather than uniform reef management — for protecting the places most likely to still hold coral after an event, and to seed recovery elsewhere. The concept carries two cautions that are routinely dropped in summary. A refugium is defined against a particular event, and a site that buffered one heatwave may not buffer a longer one. And refugia are only useful for recovery if larvae from them can actually reach the damaged reefs, which is a question about currents and larval duration, not about the refugium itself.

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