(07-05-10) Started in the year 2000, the Census of Marine Life has been a decade-long international research program uniting thousands of scientists worldwide with the goal of assessing and explaining the diversity, distribution and abundance of life in the seas. It has been supported by private sources and government agencies the world over. The final reports of the Census of Marine Life will be presented and discussed in London next October.

    Ocean explorers are puzzling out Nature’s purpose behind an astonishing variety of tiny ocean creatures like microbes and zooplankton animals – each perhaps a ticket-holder in life’s lottery, awaiting conditions that will allow it to prosper and dominate.

    The inventory and study of the hardest-to-see sea species -- tiny microbes, zooplankton, larvae and burrowers in the sea bed, which together underpin almost all other life on Earth -- is the focus of four of 14 field projects of the Census of Marine Life.

    Identifying species within these hard-to-see groups, where they are and in what numbers, and the environmental role of each, are critical for understanding the size, dynamics and stability of Earth’s food chain, carbon cycle and other planetary fundamentals.

    At the other ends of the hard-to-see scale: microbes form mats on the sea floor off the west coast of South America that explorers recently found. The mats cover a surface comparable in size to Greece and rank among Earth’s largest masses of life. The Census involves more than 2,000 scientists from 80+ nations -- one of the largest global scientific collaborations ever undertaken.

Microbes: huge in diversity, abundance and importance

    Microbial cells in the oceans’ water column number roughly 10 to the 30th (called a nonillion; expressed another way: 1,000 x 1 billion x 1 billion x 1 billion) and collectively weigh the equivalent of 240 billion African elephants. That’s 35 elephants of marine microbes per person.

    Constituting 50 to 90 percent of all ocean biomass, marine microbes are the tiniest cogs essential to planetary functioning. Yet until technological marvels of this millennium (especially high-throughput DNA sequencing) revealed the stunning extent of this microscopic world, it remained largely hidden from humankind.

    “In no other realm of ocean life has the magnitude of Census discovery been as extensive as in the world of microbes,” says Mitch Sogin of the Marine Biological Laboratory in Woods Hole, Massachusetts, and leader of the International Census of Marine Microbes (ICoMM). “Scientists are discovering and describing an astonishing new world of marine microbial diversity and abundance, distribution patterns and seasonal changes.”

    After drawing ocean samples from more than 1,200 sites worldwide, ICoMM researchers have amassed a database that includes 18 million DNA sequences of microbial life spanning more than 100 major phyla (one of the highest ranks of life in taxonomy, phyla are groupings of organisms based on their general body plan).

    Revelations about the microbial world within a single decade have led researchers to dramatically revise their estimates of diversity -- there may be up to 100 times as many microbial genera as previously thought. Genus is the category of life ranked between family and species.

    During an 11 month study in 2007, scientists sequenced the genes of more than 180,000 specimens from the Western English Channel. Although this level of sampling “far from exhausted the total diversity present,” they wrote, one in every 25 readings yielded a new genus of bacteria (7,000 genera in all).

The rare biosphere of microbes

    Also surprising scientists -- and considered one of the foremost discoveries of the decade long global Census: “the rare biosphere” of microbes. Many rare species in a sample stand opposite to a few species predominating. Wherever Census researchers looked they found many species in a sample represented by less than one in 10,000 of all individuals, including one-off singletons.

    Evidently many candidates, now rare, lie in wait to become dominant species if changes favor them. The theory recently gained steam thanks to an ICoMM study of microbes adapted to conditions inside cone-like carbonate chimneys in “The Lost City Hydrothermal Field.” The field lies 15 km (9.3 miles) west of the Mid-Atlantic Ridge near the latitude of Florida and Morocco. Hydrothermal vents have been active for at least 30,000 years in the field.

    When methane and hydrogen-rich fluids just below the boiling point emerge from deep within Earth and collide with frigid seawater they build the chimneys. Through genetics, scientists determined that rare microbes in young chimneys “were commonly more abundant than in older chimneys, indicating that rare members can become dominant members when environmental conditions change.”

More than 20 million types of bacteria live in sea water

    John Baross of the University of Washington, who chairs ICoMM’s scientific advisory council, notes that with traditional methods so far experts have isolated and characterized about 20,000 marine microbes. Census research suggests that, within a particular size interval, more than 20 million types of bacteria live in sea water.

    However, Dr. Baross notes: “The total number of species of marine microbes, including both bacteria and archaea, based on molecular characterization, is likely closer to a billion. ICoMM has studied relatively few of the oceans’ microbial environments. And there are bacteria associated with each of hundreds of thousands of larger marine animals, all of which have a microbial flora in their guts and attached to their outer surfaces that have likely co-evolved with the animals. Marine animals alone may account for hundreds of millions of microbial species. This is a huge frontier for the next decade.”

    A study of sponges from Australia’s Great Barrier Reef discovered one that was host to almost 3,000 operational taxonomic units of bacteria. “Tracking and visualizing such complex populations was impossible 10 years ago,” says Dr. Baross. “Sequencing allows us to give the equivalent of an Internet URL to millions of microbes, to which we can attach all kinds of other information, like their favorite temperature and amount of salt and light.” And the variety of marine viruses may rival that of microbes. “The first census of marine viruses should be a goal of the next decade,” he adds.

Text: Mark Montoya / coml.org
Pictures: Census of Marine Life