How do species travel across the ocean?

Vents species, sold seep species: a same origin?

Communities of organism that develop around deep-sea hydrothermal vents share many characteristics with those encountered at cold seep areas, rich in methane, on continental margins, in particular near canyons that great rivers (Mississipi, Zaïre) dig.

Although few species are common between these two habitats, the relatedness of the fauna is obvious at higher zoological classification levels. For example, we find closely related species of mussels, clams, shrimp of the family Alvinocarididae, numerous scale-worms … We can then think that these communities that are relying on bacterial production using the fluids that are rich in reduced compounds have a common origin and differentiated through time by successive isolations during the opening of the Atlantic.

However, the study of the communities from cold seeps of both sides of the Atlantic (Gulf of Mexico, Barbados, and Gulf Guinea) also revealed that two distant sites can possess very closely related communities, and that several important species are shared.

Goals of the Serpentine cruise

One of the goals of the project “ChEss” in the international programme Census of Marine Life is to study the dispersion of species across the Atlantic equatorial belt between the Gulf of Mexico and the margin of the Gulf of Guinea. One of the objectives of the Serpentine cruise, integrated in an international effort is to understand if the hydrothermal sites on the mid-Atlantic ridge, and particularly the areas rich in methane, could have been used as stepping stones for some amphi-Atlantic (found on both sides of the Atlantic) zoological groups.

Indeed, the larvae, that are the most likely way of dispersal, do not possess life-times that are compatible with a transport by deep currents whose speed is usually slow (several tens of years to cross the Atlantic). In addition, the opening of the Atlantic, that occurred during the Cretaceous (65 millions of years) seems too old to explain the distribution of those species that, without exchanges, should most likely have diverged.

So, what are the most likely mechanisms? Some authors suggest the existence of teleplanic larvae (whose development is slowed down in cold waters) or the existence of relay areas based on the bacterial decomposition of whale falls or sunken wood.