Scientists reveal unsuspected shark diversity from DNA in the ocean
Wednesday 2 May 2018
MARINE ecologists have shown that testing the oceans for DNA is revealing the presence of rare and vulnerable shark species in areas where they were previously thought to be extinct.
Many marine species are now missing in areas where they once were abundant and this is especially true for marine megafauna such as sharks,which have dramatically declined almost everywhere. It is unclear, however,whether this now missing or “dark diversity” of sharks is real or due to a failure to detect the few remaining animals, if any.
An international study, published today (Wed, May 2, 2018) in Science Advances by scientists in the UK, France and New Caledonia in the South Pacific, has shown that residual populations of several shark species that could not be detected through years of visual surveys, can instead be revealed by a revolutionary technology based on the retrieval of fragments of DNA (e.g. from skin, excretions, blood) left in the wake of rare animals, known as “environmental DNA” (eDNA).
Metabarcoding
Using a process called metabarcoding, the team from the Universities of Salford, UK; Montpellier, France and the French National Research Institute for Sustainable Development, New Caledonia detected the presence of more shark species in a few samples of seawater filtered for DNA fragments than observed during thousands of dive surveys and hundreds of baited video stations in New Caledonia, a French South-Pacific territory.
The results are consistent both in the remote, pristine reefs of the Coral Sea Natural Park, where sharks are observed in numbers at all dives, and near the capital city Noumea where sharks are scarce. This means that eDNA analysis has the power to detect rare and elusive species both in highly impacted and in wilderness areas.
“We were able to detect up to seven species of sharks in a single sample of water, when a maximum of three species could be observed in a single dive” said Laurent Vigliola, researcher in Marine Ecology at the French Institute for Research and Development in Noumea, and co-leader of the APEX project that is studying sharks in New Caledonia.
“The results are clear and speak for themselves” says Germain Boussarie, PhD student in Noumea, and co-lead author of the study.“With only 22 samples of water, eDNA revealed the presence of 13 shark species,contrasted to nine species observed in nearly 3,000 scientific dives and almost 400 baited videos!” adds the young scientist.
Conservation
The study reveals the potential of eDNA analysis for future conservation studies, as a complement to traditional methods to improve species detection. Nearly half of chondrichthyan species (sharks, rays and chimeras)are data deficient in the IUCN Red List, meaning that not enough information has been gathered by scientists so far to determine a protection status for these rare and elusive species.
“With a few more eDNA samples, we should be able to reveal which species of sharks are really missing, and thus illuminate the dark diversity of sharks in the impacted areas of New Caledonia” says David Mouillot, professor in Ecology at the University of Montpellier, France, and co-leader of the APEX project.
“New genomic tools like eDNA metabarcoding could bring new light to conservation by filling knowledge gaps on data deficient species,”explains Judith Bakker, PhD at the University of Salford which runs a series of postgraduate courses in wildlife conservation and environment and is due to launch a BSc Marine Biology..
Elusive megafauna
“Therefore, eDNA will play an increasingly important role in providing valuable information on threatened and elusive megafauna, and will help implement more efficient conservation strategies in the near future” adds Stefano Mariani, professor in Conservation Genetics at the University of Salford, and co-leader of the study.
And Laurent Vigliola believes this is good news for marine conservation:“Rare and elusive species such as sharks may still be out there; probably only a few individuals left, but still there. We now need to be smart enough toallow these animals to rebuild larger populations and be thriving again, as it should always have been in the oceans”.
The paper Environmental DNA illuminates the dark diversity of sharks Sci. Adv. 4, eaap9661 2018 is freely available online at http://advances.sciencemag.org/content/4/5/eaap9661
The research is also featured as 'top story' in today's The Conversation news website.
For further information about this research and paper, please contact Stefano Mariani
Professor of Conservation Genetics / Assoc.Dean Research Peel316, University of Salford, Manchester M5 4WT, UKT: +44(0)0161 295 6913 / m +44(0)7712 689871 s.mariani@salford.ac.uk / www.marianilab.org
Find out more
Gareth Hollyman, Senior Press & PR Officer (Science)
0161 295 6895 g.b.hollyman@salford.ac.uk
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