When You Think "Hydrothermal Vents", You Shouldn't Think "Tube Worms"

Riftia pachyptila, the weird, iconic giant of hydrothermal vents. Creative Commons Sabine Gollner et al.; click image for link and license.

In 1977, scientists and the world were shocked to discover the first deep-sea hydrothermal vent community at the Galapagos Rift in the eastern Pacific (see a great story on this at NPR here). At this site, chimneys spewing black, superheated and chemically supersaturated water towered over fields of blood-red tube worms encased in white sheaths, giant deep-sea clams, mussels and anemones. Biologists, who had long considered the deep, sunless places of earth to be lifeless death zones, were flabbergasted.

Since then, when you think ?black smokers? or ?hydrothermal vents?, you probably think ?tube worms?. And with reason: the gutless, endosymbiotic, spectacular 7-foot+ deep-sea worms are iconic.

But that would be very, very wrong. For the majority of deep-sea vents are not home to vent worms, which as best as I can tell from this Encyclopedia of Life map and from my own reading are right now only known from the east Pacific. The dominant species at all the vents along the mid-Atlantic ridge, for example, are shrimp and mussels. And in the last two years scientists probing the East Scotia Ridge ? some 8500 feet from the surface ? stumbled into a deep-sea black smoker system encrusted with, of all things, yeti crabs.

The ultimate in high-density housing. Credit: Oxford University, used with permission; Click image for link to source paper

Yup. Yeti crabs (In case you?re at a loss as to how they got their name, see this). The impressively (and hairily) armed denizens of the South Pacific were only discovered in 2005. The news was announced yesterday in an article in PLoS One, and was also covered here at Scientific American.

Along with the yeti crabs was a community the likes of which has never been seen before at a deep sea vent. In the picture above at right, those aren?t seaweeds or even coral. They are stalked barnacles new to science. There were new anemones (look for the photos of them in Figure 3 here) and a new snail, and a new seven-armed predatory sea star. And there was a ghostly ocotopus species, also new to science, that seemed to be attracted ? out of curiosity? ? to the ROV?s lights.

I'm ready for my closeup, ROV Isis. Credit: Oxford University, used with permission; click image for link to source paper.

But just as surprising as what was there, was what wasn?t. There were none of the tubeworms, polychaetes (bristly worms), clams, mussels, predatory crabs, or shrimp typically found at other deep sea vents in the Pacific, Indian, and Atlantic Oceans. At the same time, there were a few species that overlapped with vents in the west, south, and east Pacific, and the Mid-Atlantic Ridge. Though the yeti crab species is new, it has relations on the Pacific-Antarctic Ridge and at cold seeps off Costa Rica. In particular, the chemosynthetic (making food from inorganic chemicals) bacteria and other microbes at the base of the food chain at the Antarctic vents were similar to those found elsewhere.

The take home here, then, is not that this new vent system is from another planet (although it?s definitely more unusual than most, for reasons gone into in the Sci Am article), but that there are actually *many* different kinds of vent community on Earth, and that most don?t involve tube worms. The authors made an attempt to calculate just how many types there are. When their new data from the Southern Ocean were added to existing data, computers calculated that there are most likely 11. Here?s a map they made showing this; the two new East Scotia Ridge vents are shown as blue circles. As you?ll note, there?s a lot of different vent communities out there. Probably only about 2 or 3 host tube worms, though the rest, to be sure, are home to their own set of fascinating weirdos.

A model of global deep-sea vents that presents 11 types. The two new East Scotia vents are shown as blue dots. Figure 6 in Rogers et al. Creative Commons license. Click image for link to article.

In a commentary that alongside the article, Steven Chown from Stellenbosch University in South Africa notes that although the new vents are well protected by Antarctic treaty, many of the other vents on Earth are not, and, given their uniqueness and rarity, that is a problem. As it turns out, the very thing that makes them hospitable to life ? the hot water precipitating minerals ? also creates rich metallic sulfid ore veins in the vents. In fact, most of the ore veins found on Earth are ancient hydrothermal vent systems, although these can form on dry land, too, at places like Yellowstone, or deep within the earth. But deep sea hydrothermal vents seem to be particularly good at concentrating metals. Chown points out that at the Solwara Vent off Papua New Guinea, ore deposits may contain 7% copper by weight. Ore at copper mines on land contain about a tenth of that.

In the absence of rules or protection, mining deep-sea vent system will happen (see this enlightening article from the Economist in 2009), and indeed is about to happen. Nautilus Minerals of Canada plans to start mining the Solwara Vent in 2013, although, Chown notes, ?environmental impacts at this site will, apparently, be well managed.? Neptune Minerals of Australia was granted exploration licenses for sites off Papua New Guinea, Micronesia, and Vanuatu, and in 2008 applied for mining licenses for two site off New Zealand, according to the Economist. Russia has its eye on four sites on the Mid-Atlantic Ridge, and China is exploring the Indian Ocean.

Chown also points out that in July 2011, the International Seabed Authority approved four new applications for mineral exploration of polymetallic sulfides in association with hydrothermal vents. The current plan is to explore only inactive vent systems devoid of vent life, but all these developments obviously make some nervous that in international waters, in the absence of a conservation policy agreed to by all, all bets could be off. It?s not as if there?s anyone else down there watching what?s going on. And satellites can?t see the seabed, or at least not in the way you can check out the contents of your neighbor?s backyard via Google Earth.

Now I?m not trying to villainize mining companies here. Let?s not be naive about where the metals and rare earth elements in your iPad, iPhone, laptop, and flat-screen TV come from (although you should, perhaps, consider buying used when possible, and recycling them responsibly when you?re done playing with them). The lifestyle you enjoy is made possible by mining (and farming and logging). But in a world where the Chinese entertain semi-serious thoughts of strip-mining the moon (not to mention the seabed), perhaps we as a global society should formally set certain sites ? some suggest all active vents; others most ? off-limits to mining. It?s our responsibility ? not theirs ? to set clear, uniformly enforced rules for the mining companies to play by. If you?re interested in learning more about this issue, InterRidge, a non-profit international conservation organization, is heavily involved in it.

One final note. Buried at the end of the new PLoS paper was an aside mentioning that in 1966, a seafloor photograph was taken 7,800 feet down at the East Scotia Ridge. The photograph clearly shows animals similar to the ones scientists just (re?)discovered at East Scotia. So it seems the first hydrothermal vent community was actually discovered ? but not recognized ? in 1966, 11 years before the legendary descent to the Galapagos Rift. Who knows if anyone ever looked at the picture in detail. One would assume someone at least glanced at it. Perhaps because that person didn?t expect, and couldn?t conceive of, anything so wonderful as deep sea hydrothermal vents, they weren?t able to see the magic right in front of their eyes.

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Source: http://rss.sciam.com/click.phdo?i=d4104ebea06082f3e1937560815043de

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