Tiniest creatures may reveal health of oceans
SEATTLE — It was a typical onboard encounter: two strangers, adjoining airline seats, small talk to pass the time.
They talked about what they did. Virginia Armbrust, a plankton ecologist at the University of Washington in Seattle, described the critical roles plankton play in sustaining life on Earth. At which point, her fellow traveler asked a disarmingly simple question: "So how are they doing?"
It hit like a jolt of mid-flight turbulence. Dr. Armbrust recalls she didn't have a good reply; no one really knows how well the carbon-grabbing, oxygen-making organisms are doing. It marked a turning point in Armbrust's thinking. Answering that question "became my goal," she says.
Armbrust and an international team of researchers took a significant step toward that goal this fall when they published the genome - a genetic parts list - for a tiny, glass-encrusted plankton known as a diatom.
In an office next to Armburst's, Gabrielle Rocap leads one of several teams worldwide conducting similar studies on more of the ocean's smallest inhabitants. Their aim: to reach the day when scientists can take the biological pulse of the ocean by interrogating the genes of the tiniest organisms that live there.
Such data would help researchers anticipate how environmental change - everything from land-borne pollution to global warming - affects ocean ecosystems and the atmosphere.
"We're looking for canaries in the coal mine," Armbrust says. Many people focus on larger, charismatic creatures such as whales and other marine mammals. "But you'd like to look at phytoplankton. They're at the base of the food web and they respond to changes immediately. If you see changes in marine mammals, it's too late."
Armbrust and Dr. Rocap work with the phytoplankton equivalent of Mutt and Jeff. At one end of the scale sit the diatoms. These single-cell creatures, which can range in size from roughly 1/10th the width of a human hair to a few millimeters, encase themselves in exquisitely patterned silica shells. The creatures, which exist in at least 100,000 known species, are ubiquitous along coasts and in freshwater habitats. Diatoms alone are estimated to scrub roughly as much CO2 from the atmosphere each year as all the world's rain forests. In coastal environments, they account for as much as 90 percent of the organic matter generated through photosynthesis.
At the other end sit tiny cyanobacteria that, like diatoms, use sunlight to convert nutrients and carbon dioxide into carbon-rich food and oxygen. These are found largely in the open ocean.
In terms of size, the difference is huge. If cyanobacteria were salmon, diatoms would rival the local Bainbridge Island ferry, Rocap says. "Does it matter if your carbon is in salmon or car ferries? Yeah, it makes a big difference in who can get at that," she says. So a change in their relative abundance can have a profound effect on the food chain.
In both cases, having genomes in hand is opening new windows on how these creatures function and is expected to yield a wealth of insights into the factors that can influence their well-being.
Her subject, the diatom Thalassiosira pseudonana, is one of the simpler diatoms to study. Its physical traits are well-known, and it's "cosmopolitan," she says, allowing researchers to apply their results broadly.
One surprise: Although, like a plant, it loves nitrogen, particularly in the form of ammonia, it handles that ammonia as an animal does, through a urea cycle. In animals, the cycle rids them of ammonia as a toxin. In diatoms, it appears to be a biological contradiction. "It's like: What?!? How is that possible?" Armbrust asks. It's one of several mysteries about the organism researchers hope to solve.
For Rocap, two types of cyanobacteria took center stage - with names certain to quickly fall from the list of monikers parents consider for their newborns: Prochlorococcus MED4 and Prochlorococcus MIT9313. Each is found in the open ocean, but each is found at a different depth. They are giving new meaning to the phrase "genetic diversity."
They pick up genes "from organisms they're not even related to - not their parents, not even their species. It's as though humans could exchange genes with a fungus," Rocap says. "We know this is possible [in cyanobacteria], but the more genomes we sequence, the more we see this is active and extremely influential in the evolution and ecology of these organisms."
These observations are necessarily broad. More-detailed links between genes, an organism's functions, and the environment will require much more detective work. Yet these and similar efforts are raising the prospect that taking the genetic pulse of the ocean is not far off. Already, scientists and engineers are thinking of ways to equip moored buoys or robotic underwater vehicles with special computer chips with genetic tools. Data could leave the vehicle, ricochet off a communications satellite, and land in a database available to scientists worldwide.
Out of both genome projects are coming "new views of the diversity of life in the ocean," Armbrust says. "We're just beginning to prop open the door to see this incredible diversity. We're in a time of exploration during a time of environmental change." Exploration "makes it exciting," she says, and environmental change "is what motivates us."
• Although they lack the roots, leaves, and other structures typical of plants, algae capture more of the sun's energy and produce more oxygen (a byproduct of photosynthesis) than all other plants combined.
• Algae vary greatly in size: from microscopic phytoplankton (1,000 could fit on the head of a pin) to seaweed that stretches 300 feet from the ocean bottom to the water's surface.
• By some estimates, a form of algae known as diatoms pull as much carbon dioxide from the atmosphere as all the rain forests combined.
• Another form of algae, called carrageen, is used in brownie mix, cottage cheese, infant formula, toothpaste, relishes, and pet food.
Sources: Bioproject, NASA