Species intolerant of changing climate might avoid extinction within refugia buffered from extreme conditions. Refugia have been observed in the fossil record but are not well documented or understood on ecological time scales. Using a 37-year record from the eastern Pacific across the two most severe El Niño events on record (1982–1983 and 1997–1998) we show how an exceptionally thermally sensitive reef-building hydrocoral, Millepora intricata, twice survived catastrophic bleaching in a deeper-water refuge (>11 m depth). During both events, M. intricata was extirpated across its range in shallow water, but showed recovery within several years, while two other hydrocorals without deep-water populations were driven to regional extinction. Evidence from the subfossil record in the same area showed shallow-water persistence of abundant M. intricata populations from 5000 years ago, through severe El Niño–Southern Oscillation cycles, suggesting a potential depth refugium on a millennial timescale. Our data confirm the deep refuge hypothesis for corals under thermal stress.

Depth range
2- 25 m

Mesophotic “mentions”
3 x (total of 6673 words)

Classification
* Presents original data

Fields
Ecology
Connectivity
Paleoecology
Long-term monitoring
Oceanography

Focusgroups
Hydrozoa

Locations
Panama - Pacific Ocean

Platforms
SCUBA (open-circuit or unspecified)
Coring / drilling
In-situ instrumentation
Surface-deployed sensors and samplers