204 — Does the Mid-Atlantic Ridge affect the distribution of abyssal benthic crustaceans across the Atlantic Ocean?

Prior to reading this paper, I sort of imagined that deep sea ecology varied with geography, but I didn’t have a good justification for that. After all, my interactions with the abyssal deep sea are pretty limited. My mental model of the deep sea abyssal zone is infinite plains of darkness with sporadic vents and seamounts or volcanos. If you don’t like heat, walk or swim around the vents. Simple.

But no — there are obviously obstacles that are impassible. A perfect example of this is the Mid-Atlantic Ridge (MAR), the gash between the Eurasian, North American, African, and South American tectonic plates. The divergent boundary spreads about an inch per year. (It also runs directly through Iceland, so if you’re planning on buying any real-estate there, that’s a pretty solid bet.)

According to this research, which used data from the Vema-TRANSIT expedition, this constructive plate boundary also serves as a definitive dispersal boundary for certain types of the surveyed abyssal fauna (though most swimming species and some non-swimming species are able to cross easily). (Recent biomolecule assays also confirmed that what appear to be a widely dispersed abyssal species are often more likely to be many small, localized colonies which similar genetics or morphology.)

The Vema Fracture Zone is a large gently sloping valley that crosses the ridge between the Demerara and Gambia abyssal plains. In this region, it appears that species are often able to cross, but most crawling or burrowing species do not. Because of the topography of this zone, water currents and temperatures are affected dramatically, and a cold water current passes across the valley. That is, even though the zone represents a more tractable traversal point based upon its topography, the environmental factors — which cannot be established from surface imagery — may prevent species from endeavoring across the MAR.