Stop at the port

These are little bits of ocean like no other, home to inhabitants like no other. Frédérique Viard, a researcher at Isem* is interested in the biodiversity of port environments, where pressures are strong and evolutionary processes sometimes rapid.

The port of La Seyne-sur-Mer © Frédérique Viard

Concrete, noise, artificial light, hydrocarbons; a ring-road atmosphere that actually describes... a port. " A unique marine habitat," notes Frédérique Viard. A unique ecosystem that the biologist from Montpellier's Institut des sciences de l'évolution is scrutinizing to find out more about its occupants. " Harbours are a new urbanized marine habitat that will encourage the establishment of original assemblages of species adapted to these particularly selective environments ", emphasizes the specialist who navigates between ecology and evolutionary biology.

This seemingly hostile environment represents a " hot spot for introductions ", where species from other parts of the world arrive to settle down. This phenomenon accelerated in the 20th century with the globalization of maritime trade," emphasizes Frédérique Viard. Today, in some taxonomic groups, up to 20% of species in ports are introduced, compared with well under 1% in natural ecosystems. Ballast water, the hulls of merchant ships and pleasure boats alike, the slightest crevice on a boat is a possible refuge for these stowaways. " Canadian scientists have counted up to 175 different species on the hull of a single merchant ship!

Redistributing the cards

Once in port, these non-native species mix with local species, generating " heterogeneous assemblages of native and introduced species that could never have formed naturally, and without human intervention ". But once brought together, they can reshuffle the deck in terms of species richness and genetic diversity. " Some species are distant cousins of local species, separated for millions of years, which today find themselves together in ports and which sometimes manage to cross-breed, giving rise to new lineages ", explains Frédérique Viard, who describes, for example, the unlikely union of two strange underwater animals that were never supposed to meet: the Asian cione and its European cousin, which can produce hybrid offspring. Other researchers have also observed genes in a fish species that provide protection against hydrocarbon toxicity, which comes in handy when you live in a polluted environment; but these genes were passed on by a closely related introduced species, in which this adaptation had previously appeared.

Biodiversity in the making

" These changes can be rapid, as selection pressures are strong in harbours and populations are genetically diverse," stresses the biologist. These characteristics make ports veritable open-air laboratories for ecologists and evolutionary biologists. And to better identify the new species introduced into these unique labs, researchers are using environmental DNA: recovering DNA left behind by living organisms in seawater samples and comparing it with data from reference databases to find out which species it relates to. " Numerous ports on the Channel-Atlantic and Mediterranean coasts have been sampled as part ofthe MarEEE project," explains Frédérique Viard, for whom ports are " the crucible of a new biodiversity in the making ".

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