Deep coral reefs should not be relied upon as a “lifeline” for shallow reefs, a new study by University of Queensland marine scientists argues.
Often highlighted as important ecological refuges, sections of coral reefs 30 to 60 metres deep can offer protection from the full force of climate change-related impacts, such as intensifying storms and warm-water bleaching.
However new research led by Dr Pim Bongaerts, a Research Fellow at UQ’s Global Change Institute (GCI) and ARC Centre of Excellence for Coral Reef Studies, questions the role of deep reefs as a source of new corals for damaged shallow reefs.
“Deep reefs share coral species with the shallow reef, which has led to the idea that deep reefs could be an important source of larvae and help ‘reseed’ shallow reefs,” Dr Bongaerts said.
“We argue this concept of deep coral populations ‘reseeding’ shallow-water counterparts may be relevant to some species, but is ultimately unlikely to aid more broadly in the recovery of shallow reef.”
Given the impossibility of tracking movements of individual coral larvae on the reef, understanding the connectivity between shallow and deep coral populations relies on methods that assess genetic similarity .
The team focused on the relatively isolated reef system of Bermuda in the Western Atlantic, where they screened the genomes of more than 200 individual coral colonies from shallow and deep water, belonging to two coral species with similar depth distributions on the reef.
The study demonstrated the extent of connectivity between shallow and deep populations could differ greatly between species on a reef, and can be strongly affected by natural selection processes that vary across shallow and deep reef environments.
Director of GCI, and co-author, Professor Ove Hoegh-Guldberg said deep coral reefs have been touted as holding hope for shallow reefs badly damaged by bleaching events.
“Our results, however, contribute to a growing body of evidence that the role of deep reefs in shallow reef recovery is likely to be very limited,” he said.
According to Dr Bongaerts, the study highlighted that in the face of increasing disturbances, coral reefs are unlikely to just `sort themselves out`.
“Instead, the responsibility for their future lies with us,” Dr Bongaerts said.
“If we want to have any chance of preserving these unique and diverse ecosystems, it is crucial that we start curbing our emissions and divest from fossil fuels.”
The research, published in Science Advances, was undertaken as part of the XL Catlin Seaview Survey, funded by XL Catlin in partnership with The Ocean Agency, GCI at UQ, and the ARC Centre for Excellence in Coral Reef Studies at the University of Queensland. The research was carried out with the support of the Bermuda Institute of Ocean Sciences and the Bermuda Aquarium, Museum and Zoo.