Smith et al. 2016

scientific article | Global Change Biol | open access

Caribbean mesophotic coral ecosystems are unlikely climate change refugia

Smith TB, Gyory J, Brandt ME, Miller WJ, Jossart J, Nemeth RS


Deeper coral reefs experience reduced temperatures and light and are often shielded from localized anthropogenic stressors such as pollution and fishing. The deep reef refugia hypothesis posits that light-dependent stony coral species at deeper depths are buffered from thermal stress and will avoid bleaching-related mass mortalities caused by increasing sea surface temperatures under climate change. This hypothesis has not been tested because data collection on deeper coral reefs is difficult. Here we show that deeper (mesophotic) reefs, 30-75 m depth, in the Caribbean are not refugia because they have lower bleaching threshold temperatures than shallow reefs. Over two thermal stress events mesophotic reef bleaching was driven by a bleaching threshold that declines 0.26°C every +10 m depth. Thus, the main premise of the deep reef refugia hypothesis, that cooler environments are protective, is incorrect; any increase in temperatures above the local mean warmest conditions can lead to thermal stress and bleaching. Thus, relatively cooler temperatures can no longer be considered a de facto refugium for corals and it is likely that many deeper coral reefs are as vulnerable to climate change as shallow water reefs.

Research sites
Depth range
6- 75 m

Mesophotic “mentions”
144 x (total of 6352 words)

* Presents original data
* Focused on 'mesophotic' depth range
* Focused on 'mesophotic coral ecosystem'

Long-term monitoring
Climate Change

Scleractinia (Hard Corals)

US Virgin Islands

SCUBA (open-circuit or unspecified)
Surface-deployed sensors and samplers

Author profiles