For decades the monk seal, among the rarest pinnipeds in the world and the only one present in the Mediterranean Sea, was considered extinct in the waters of the Italian seas, until the recent sightings in the Tyrrhenian and Ionian Seas, which have led to the hypothesis of its return. In order to map its presence, researchers at the University of Milano-Bicocca have developed an innovative and non-invasive detection method, based on the recovery and analysis of environmental DNA (eDNA) from water samples taken in the Mare Nostrum. The first tests and the results of the monitoring actions have given a positive feedback, anticipating some of the recent reports of the marine mammal off the Tuscan and Sicilian coasts, in little frequented stretches of sea.
The method was described in an article entitled “A species-specific qPCR assay provides novel insight into range expansion of the Mediterranean monk seal (Monachus monachus) by means of eDNA analysis”, just published in the scientific journal “Biodiversity and Conservation” (DOI: https://doi.org/10.1007/s10531-022-02382-0). First author Elena Valsecchi, molecular ecologist of the department of Environmental and Earth Sciences of the University of Milano-Bicocca and professor of Marine Vertebrate Zoology.
At the base of the method, an assumption: every living organism leaves a trace of its passage and this is revealed by its DNA remaining in the environment. For example, for the monk seal, from the DNA that remains in the mass of water in which it moves. Elena Valsecchi coordinates the Marine environmental eDNA Group of the Milanese university, which for two years has promoted the project “MeD for Med - Marine environmental DNA for the Mediterranean”, a marine biodiversity monitoring system based on the analysis of the environmental DNA contained in water samples collected by ferries along the commercial routes. A project developed thanks to the co-financing of the Bicocca, University of Crowdfunding programme of the University of Milano-Bicocca and described in an article published last August in “Frontiers in Marine Science” (DOI: https://doi.org/10.3389/fmars.2021.704786).
In order to develop a molecular strategy able to intercept, from the analysis of simple marine water samples, the presence of the monk seal, once widespread throughout the central-eastern Mediterranean basin but today concentrated mainly in the Aegean Sea, Elena Valsecchi has identified “informational” regions of the mitochondrial DNA of the pinniped, that is, target sequences that are found only in this species. The researchers were thus able to develop specific probes to be able to “fish” within a mixture of millions of DNA molecules from the most disparate animals – such as the one present in an environmental DNA sample taken from the sea – the DNA of the monk seal: a sort of “molecular magnet”.
In collaboration with Antonia Bruno, microbiologist of the department of Biotechnology and Biosciences, the screening of “real” environmental samples was carried out. The molecular probes were then tested in the field, through the comparison with a wide spectrum of samples, some of which (positive samples) containing the DNA of the monk seal, such as those taken in the waters of the Atlantic Ocean around the Portuguese archipelago of Madeira, where there is a small resident population of about thirty specimens of monk seal, thanks to the collaboration of the Instituto das Florestas e Conservação da Natureza of Madeira.
The tests demonstrated the efficiency of the probes in intercepting the presence of the marine mammal and convinced the researchers to experiment with them in environmental DNA samples collected in the Mediterranean, as part of other research projects carried out by the Marine eDna Group. These are the results: “We detected the presence of the species – says Elena Valsecchi – in about 50 percent of the samples taken off the island of Lampedusa in the summer of 2020 and in some samples taken between 2018 and 2019 from a ferry off the Tuscan archipelago as part of the Med for Med project, along the Livorno-Golfo Aranci route (Corsica Sardinia Ferries)”.
The effectiveness of the test has been confirmed in reality. “The analysis of about 50 water samples taken in the Italian seas both under the coast and on the high seas – continues the molecular ecologist – has anticipated some of the most important reports and sightings of monk seals that have occurred recently in Tuscany and Sicily and has revealed their presence in hitherto unexplored stretches of the Mediterranean.”
The applications of this molecular detection system are manifold. “It will be possible to monitor areas where the presence of the monk seal is already known – observes Emanuele Coppola, documentary filmmaker who has worked on monk seal for decades, as well as president of the Gruppo Foca Monaca APS and co-author in the publication – in order to estimate the seasonal passage of the pinnipeds and the degree of fidelity to the site, even during the winter seasons or at night, and to keep under observation, in an absolutely non-invasive way, coastal sites that, due to their physical conformation, constitute the potential habitats of choice for the monk seal, such as caves sheltered from the force of the sea and with internal beaches ideal for giving birth.” This will encourage the study and the research on the species, the conservation of the sites and the protection of the monk seal.
In this sense, the University of Milano-Bicocca, Gruppo Foca Monaca APS and numerous other partners are now engaged in the “Spot the Monk” initiative, an ambitious Mediterranean sampling plan that also involves several citizen science programmes, with different crews and boats involved in the collection of samples.