Deep reefs of the Great Barrier Reef offer limited thermal refuge during mass coral bleaching

Deep reefs of the Great Barrier Reef (GBR) offer limited thermal refuge during mass coral bleaching events, despite initial assumptions. While summer upwelling provided temporary relief at 40 meters depth, it later subsided, leading to anomalously warm temperatures even in deeper zones. Bleaching impacts were severe but significantly lower than in shallower reefs—40% of colonies bleached and 6% dead at 40 meters compared to 60-69% bleached and 8-12% dead at 5-25 meters. This study highlights the transient nature of deep reef protection, challenging the notion that mesophotic zones can serve as broad ecological refuges from thermal stress.

Frade, P. R., Bongaerts, P., Englebert, N., Rogers, A., Gonzalez-Rivero, M., & Hoegh-Guldberg, O. (2018). Deep reefs of the Great Barrier Reef offer limited thermal refuge during mass coral bleaching. Nature Communications, 9(1). https://doi.org/10.1038/s41467-018-05741-0