The color of the ocean can range from steel gray to green or sky blue, but during a research cruise off the coast of Chile on board the R/V (research vessel) Melville in December, Angelicque White saw something unusual. “We were sitting on the bow of the boat watching the whales go by. One whale, two whales, 10 whales — it was amazing,” she says in a video from the ship. “And suddenly we realized we were in this red sea. You can see these strands, these filaments of bright, bright red. It’s gorgeous.”
Scientists ran up on the deck to lower fine-mesh nets into the water, hoping to catch a few of the organisms responsible for this colorful display, but their efforts were in vain. Their tiny quarry slipped right through the nets. Finally, using that most sophisticated of oceanographic instruments, the plastic bucket, they brought up a water sample and put a drop under a microscope. According to White, what they saw was as puzzling as it was exciting. “We saw these tiny . . . maybe dinoflagellates (plankton associated with ‘red tides’). They’re motile; they’ve got flagella. And these things are just zooming around,” says White. Other experts suspected the organisms were ciliates, which are common in the Pacific Ocean plume from the Columbia River (positive identification — and a $20 scientific bet — will be settled by genomic analysis). Their difficulty in identifying the organisms is testimony to the huge microbial diversity of the oceans.
It was another day at sea for Oregon State University oceanographers Ricardo Letelier, Joe Jennings Jr. and White. They had joined colleagues from Chile, Spain, Woods Hole, MIT, UC-Santa Cruz and the University of Hawai’i at Manoa on a 2,300-mile research expedition from the rich fishing grounds off Chile to one of the world’s least productive seas, located around Easter Island. Their purpose: to understand how microbial diversity changes from areas of high to low productivity. As scientists in OSU’s College of Oceanic and Atmospheric Sciences and members of C-MORE — the Center for Microbial Oceanography: Research and Education — they are studying the under-appreciated but most abundant life forms on the planet. C-MORE is one of 17 Science and Technology Centers funded by the National Science Foundation.
Every Breath We Take
To appreciate their mission, it helps to know a little about ocean microbes. They help to control the chemistry of the atmosphere by producing and recycling carbon dioxide and other greenhouse gases. And those that conduct photosynthesis — the phytoplankton — supply much of the oxygen we breathe. In fact, some scientists suggest that we can thank one of the smallest and most abundant of them, Prochlorococcus, for every fifth breath we take.
“These organisms are oxygenating the planet. They’re the base of the food web. Yet we know very little about how shifts in microbial diversity and productivity impact ecosystem function,” says White.
Better understanding won’t come too soon. Last summer, a report in the journal Nature by a Dalhousie University research team in Nova Scotia concluded that phytoplankton have been declining in the world’s open oceans at the rate of about 1 percent per year for the last century. While that study has generated debate in the scientific community, future declines are likely as the oceans warm. That’s because as temperatures increase, the seas will separate more strongly into nutrient depleted surface and nutrient rich deep-ocean layers, reducing the nutrient upwelling that fertilizes plankton at the sunlit ocean surface.
Letelier agrees that warmer oceans will likely mean lower plankton productivity globally. However, he adds, it’s not that simple. In some areas, production is increasing. For example, through nearly 20 years of intensive study at a research site known as Station ALOHA north of Hawaii, he and other researchers have found that plankton production has increased as the sea has become warmer and more acidic.
Nitrogen for Lunch
The reason for this apparent contradiction may lie in nitrogen, a critical nutrient for plankton growth and one that is in low supply in large areas of the oceans. Most plankton depend on nitrate (a molecule composed of nitrogen and oxygen) for their nitrogen supply. Experi- ments by Letelier, White and others have demonstrated that phytoplankton that use nitrogen gas diffused into the ocean from the air instead of nitrate can multiply even as other nutrients are in decline. On top of that, as more carbon dioxide enters the water from the air, these “nitrogen-fixing” microbes may grow faster until some other key nutrient becomes limiting.
It’s also important to remember, says White, that ocean microbes have the ability to respond to changing ocean conditions. “The variability that organisms display in their expression of genes over the course of a day is huge. And scaling that capacity for adaptation up to the next 10 years, when the oceans may be more stratified, warmer, more carbon-rich, in order to try to project what microbes might do in that kind of system, is difficult.”
The OSU researchers have developed new optical methods for monitoring plankton growth and abundance. And during cruises to Station ALOHA and in the South Pacific, they run shipboard experiments to see how microbial communities will respond to water that is warmer, more acidic or supplied with different forms and amounts of nutrients such as iron and phosphorus.
They are also pioneering new ways of conducting experiments. In one 2008 study at Station ALOHA, they used the motion of ocean waves to pump water from 300 meters deep in the ocean to the surface. They wanted to see if a disturbance to the microbial ecosystem — in this case a sudden shot of nutrients from below — would stimulate plankton production.
Unfortunately, the study ended prematurely. The pumps broke from the stress of ocean waves before the researchers could see an impact. “We know a lot about how upwelling works and the physics of the ocean,” Letelier said after the study ended, “but there also are things we don’t know, which is why this study is so important. In this open ocean area near Hawaii, for example, phytoplankton blooms occur in the summer when there are almost no nutrients at the surface and the winds generally are calm. What triggers the blooms and where are the nutrients coming from? We need to know.” Lead researcher David M. Karl of the University of Hawaii is planning to repeat the effort, which was funded by the NSF and the Gordon and Betty Moore Foundation.
“It’s about understanding the base of the food web that covers 70 percent of the planet,” says White.
See videos from the South Pacific expedition organized by the Center for Microbial Oceanography: Research and Education.
See stunning photos of plankton taken by Angelicque White and her colleagues.
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