The sea without people

[LUM Magazine] - Published on December 3, 2020 in Science-Society

Not a boat in sight. Deserted beaches. No one at sea. No one except Julie Deter and David Mouillot's team* with their researchers, technicians, and divers. They are among the select few who have been able to crisscross the Mediterranean during this very unusual period of lockdown. Their goal: to study marine biodiversity in the absence of humans.

photos © Lila Desgarnier / Nadia Faure / Lola Romant / Raphaël Seguin

"It was a tremendous opportunity to obtain a true baseline of the marine environment temporarily preserved from human presence. This new baseline will make it possible to measure more accurately the state of degradation of marine biodiversity and the effect of the protections put in place," explains David Mouillot.

The team deployed several types of tools to understand marine diversity. "Visual tools, on the one hand, thanks to underwater divers who filmed exceptional images." But also hydrophones to listen to the sounds of the sea, which are normally drowned out by boat noise.

The project also used an innovative tool: environmental DNA analysis. The principle involves filtering water samples to recover DNA left behind by living organisms. This DNA is then compared with a reference database to identify the species to which it belongs. "This technique reveals the presence of rare or elusive species that are never seen when diving," explains David Mouillot. "This will enable us to determine whether species that are usually found at the bottom or offshore have moved closer during lockdown."

Researchers observed that the Mediterranean Sea benefited greatly from the absence of humans. "Fishing, boating, and even simply swimming—all these activities have an impact on coastal residents, who surely came out of lockdown while we were still in lockdown. And vice versa this summer."

* Marine Biodiversity, Exploitation and Conservation Laboratory (MARBEC) (IRD, Ifremer, University of Montpellier, CNRS) – Andromède Océanologie. Mission carried out in partnership with SpyGen, funded by the Water Agency, and with the approval of the maritime prefecture.