Sogin is now supercharging this approach. By using faster sequencing machines and targeting only one highly variable part of the rRNA gene, he and his team can sequence 200,000 pieces of DNA from a single liter. As a result, the amount of diversity they find has soared. In one sample from the deep North Atlantic Ocean, they have found more than 60,000 kinds of bacteria.
One intriguing discovery, Sogin says, is that in each sample he has studied so far there are always a few dominant kinds of microbes but also thousands more that are rare. Moreover, at each station—or even at different depths at the same station—there is a different suite of rare microbes. The large number of rare microbial species suggests that they have an important role in the oceanic ecosystem. Sogin suggests these rare species might function as a genetic archive, a fail-safe against environmental disaster.
Over many millions of years, he explains, Earth has undergone repeated environmental cataclysms. “Global warming, asteroid impact, or whatever it is—those events threaten the survival of the microorganisms. This might be a way for them to cope,” Sogin says. If there are tens of thousands of rare microbes floating in the water, all with different genes and correspondingly different abilities, there will always be a few that are adapted to the new environment. The dominant might become rare, the rare might become dominant, but the kingdom as a whole persists, albeit with an altered mix of species, which in turn alters the elemental cycles that determine the basic life chemistry of the sea.
A 2005 mission to the ice-covered Canada Basin, some
of the world's oldest waters, exposed
a new type of larvacean.
Image coutesy of R. Hopcroft,
University of Alaska Fairbanks © 2006
If so, the invisible and barely explored world of marine microbes may end up touching our own world in ways we cannot foresee. As the oceans grow warmer and more acidic from our emissions of carbon dioxide, we may once again shift the microbial balance in the ocean. “A minor change in acidity could have radical impacts, and that could lead to a cascade of effects on climate change,” Sogin says.
The realm of the very deep in the sea is as elusive as the realm of the very small—and rare species seem to be the norm there too. Away from the rocky slopes of the seamounts and midocean ridges, the ocean floor is everywhere cold and muddy, so scientists long assumed that fauna would be pretty much the same worldwide. Such “cosmopolitan” animals do exist: There are species of foraminifera (single-celled organisms with shells) that live both in Arctic as well as Antarctic mud, thousands of miles apart.
But in a series of expeditions to the Antarctic aboard the Polarstern, Angelika Brandt of the University of Hamburg has encountered different sorts of organisms. She focused on the deep seafloor, well beyond the ice shelves and the continental shelf that were her compatriot Julian Gutt’s targets. Her specialty is isopods, segmented crustaceans that thrive in the deepest stretches of the ocean. At 40 stations in the Southern Ocean, dragging a sled with a net through more than three acres of mud, Brandt found 674 species of isopod. More than 500 were new to science.
“It was astonishing,” says Brandt. “It was really high diversity.” The pattern of diversity was reminiscent of the pattern Sogin saw with his bacteria. “We had only a few species that were dominant—and many that were very, very rare. More than 50 percent of the species were found at only a single station,” she says. In many cases there was only a single specimen, which raises the question of how those poor isolated creatures find a mate.
For all its scope, even the census won’t be able to describe each species of isopod or polychaete that squirms in the deep-sea mud. But it will at least compile information on most of the species of life in the sea that are known and have been named, and estimate their geographic range. It will also estimate the abundance, in tons, of the large taxonomic groups like the crustaceans. Finally, it will try to say something about what used to live in the ocean, before we overfished and polluted so much of it, and what is likely to persist there now that it is so heavily under our influence. Last year a census study projected that, if current trends continue, all commercially fished species will follow the cod into collapse by 2050.
At present, our impact on the ocean vastly outstrips our knowledge of it. One of the tasks of the census, says Ausubel, is to try to right that balance. There is a lot we can learn just by removing our blinders, a lot that is “invisible” just because we have not looked. Maybe something as weird and new as hydrothermal vents will turn up in some place yet unexplored.
“Nobody had ever looked into the deep sea off Antarctica,” Brandt says. “Nobody ever went there to say, ‘Look, this is there.’ We tried to hypothesize about what might be there. It’s an enormous area, and it’s almost unknown.”
