Ocean Microscope Reveals Surprising Abundance of LifeWidespread bacterial colonies may play crucial role in ocean ecosystem |
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Towing an underwater video microscope across the Atlantic Ocean, two
scientists found unexpected abundances of colonial cyanobacteria that fertilize the oceans with
nitrogen. The bacteria may turn out to be “a crucial component” that
stimulates the growth of plants and animals in vast ocean regions that
might otherwise be nearly barren, they reported in the June 9, 2006,
issue of the journal Science.
Just like plants on land, microscopic marine plants at the base of the
food chain require nitrogen to grow. But the source of nitrogen,
especially in the open ocean far from coastal waters fed by runoff from
rivers and land, “represents one of the most intriguing conundrums in
oceanography,” Zbigniew Kolber, a research engineer at Monterey Bay
Aquarium Research Institute, wrote in Science.
Two scientists at Woods Hole Oceanographic Institution (WHOI) “decided
to have another ‘look’ at this problem, literally,” he wrote.
Cabell Davis of the Biology Department and Dennis McGillicuddy of the
Applied Ocean Physics and Engineering Department towed a device called
the Video Plankton Recorder (VPR) behind the WHOI-operated research
vessel Knorr from the Azores
almost back to Woods Hole. It remained in the water 24 hours a day,
taking digital photographs 30 times per seconds as it undulated
from the surface to depths of 425 feet (130 meters).
“It was the VPR’s longest tow, more than 5,500 kilometers (nearly 3,000
nautical miles), but slow—like driving a lawnmower across country at 12
knots,” Davis said.
The VPR images showed unexpected widespread populations of Trichodesmium,
bacteria
that were formerly (and inaccrately) known as blue-green algae. They
form tiny colonies of golden-brown spiky balls (called “puffs”) or
reddish rafts (called “tufts”). The fragile colonies, 1 to 3
millimeters in diameter, are visible to the eye, but are not easy to
collect or count because they tend to break apart when handled.
The VPR gave scientists the ability to look observe and count
Trichodesmium in a non-invasive way. Davis and McGillicuddy found that
Trichodesmium live not only at the surface, as scientists previously
thought, but throughout the region where light penetrates the ocean.
They estimated that Trichodesmium were two to three times more abundant
than previously believed.
Trichodesmium thrive in waters that are low in nutrients because of
their ability to use molecular nitrogen (N2) found in air and water.
They incorporate it into nitrogenous compounds that other organisms can
use. (Plants that do this, such as alfalfa, are used as “green
fertilizer” to add useable nitrogen to soil.)
“If traditional sampling has underestimated colonies in other regions
of the world, estimates of global Trichodesmium abundance will increase
dramatically, changing our perception of the importance of this
organism to the productivity of the world ocean,” Davis said.
In July, Davis and McGillicuddy towed the VPR behind Knorr to survey Trichodesmium abundance, this time through the Caribbean Sea.
The project was supported by the Richard B. Sellars Endowed Research
Fund, the Andrew W. Mellon Foundation Endowed Fund for Innovative
Research, the WHOI Ocean Life Institute, the National Science
Foundation, and the National Aeronautics and Space Administration.
Posted: July 25, 2006 [top] |
