How many coral reefs are there in the world? Nobody knows. How can we truly know the extent of anthropogenic coral bleaching and degradation if we lack data on the extent of coral ecosystems?
The shallow coral reefs that we all know are like the tip of an iceberg - they are the more visible part of an extensive coral ecosystem that reaches into depths far beyond where most people visit. The invisible reefs, known as mesophotic (“intermediate light”) coral ecosystems (MCEs), are widespread and diverse. However, they remain unexplored in most parts of the world.
Mesophotic reefs exist only in the tropics and should not be confused with deeper, cold water reefs.
Light-dependent corals can live up to a depth of 150 m in clear waters.
A new report titled Mesophotic Coral Ecosystems: A lifeboat for coral reefs? asks whether MCEs can provide a “lifeboat” for shallow coral reefs which are suffering decimation from rising sea surface temperatures and other anthropogenic impacts.
“The fact that we don’t know where many of these reefs are means we could be wrecking them already – from pollution, poor fishing practices or other activities. For that reason, mesophotic reefs should be included in management and conservation plans,” says Peter Harris, Managing Director of GRID-Arendal and one of the editors of the report.
To buy coral reefs more time and to support recovery of reefs that have bleached severely, some researchers are looking deeper for answers. They are studying submerged, light-dependent reefs to see if they may serve as lifeboats for nearby, connected shallow reefs that have been damaged by repeated bleaching. Mesophotic coral reefs are one of the few remaining ecosystems on earth to remain largely unexplored.
“While they are deeper and more remote than shallow coral ecosystems, mesophotic reefs are still subject to some of the same effects such as bleaching and habitat destruction,” says UNEP Executive Director Achim Steiner. “We are just beginning to understand them, but in some locations they may resist the most immediate impacts of climate change, and may be able to help re-seed damaged or destroyed surface reefs and fish populations.”
The lifeboat report’s main recommendations are: to locate where mesophotic reefs exist, with a priority in the equatorial Indo-West Pacific and eastern Atlantic; to increase our understanding of how they are connected to shallow reefs in order to understand the extent to which they can be used as a refuge for, or to reseed, shallow reefs; and to raise awareness among managers and policymakers of the importance of their ecosystem service values and encourage measures to protect them.
“Tropical coral reefs support millions of people, providing jobs and food; their conservation and wise management is a global priority,” says UNEP corals expert Jerker Tamelander.
