When biologists from the University of Connecticut wanted to take their laboratory's $85,000 DNA sequencer out to the Sargasso Sea in the Atlantic, the manufacturer, Applied Biosystems, balked. The warranty did not cover oceanographic expeditions. Even J. Craig Venter, famous for his role in decoding the human genome, had frozen his microbial samples from the Sargasso Sea for sequencing back on shore. His results showed that the surface water in the balmy sea around Bermuda teems with genetic material. The biologists from Connecticut wanted to go deeper into the ocean--and go beyond microbes--to test for diversity among the animals at the base of the food web. Working with a sequencer at sea would give them the best results.
The researchers are part of the Census of Marine Life, an international network of marine scientists that began a mission in 2000 to identify every living creature in the ocean by 2010. To this end, Peter Wiebe of the Woods Hole Oceanographic Institution designed a filter system of fine-mesh nets on a deepwater trawl. Onboard the National Oceanic and Atmospheric Administration's Ronald H. Brown, Wiebe, the chief scientist, and his team used the net device to scour the Sargasso Sea. Lashed down with a bungee cord in an air-conditioned room sat a brand-new, 140-kilogram DNA sequencer. Theirs was the first expedition to identify marine animals from 5,000 meters deep and sequence their gene markers, or "bar codes," while on the ship.
Ann Bucklin, director of the Marine Sciences and Technology Center at the University of Connecticut, presented the preliminary results in Amsterdam on May 15. She says this research will provide a baseline for measuring how pollution, overfishing, climate change and other human activity affect zooplankton and their environment.
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During the 20-day expedition, 28 experts from 14 nations collected 1,000 individual specimens, including 120 species of fish, some new to science, and hundreds of species of zooplankton. Zooplankton are the drifting and swimming animals first in line to eat algae and other plant life, called phytoplankton. They also eat one another, and some can even take down small fish. Many organisms that spend their adult life stuck on the bottom of the seafloor start out as zooplankton in their larval stage. Whatever happens to zooplankton in the ocean has an immediate impact on the rest of the marine food web.
To examine the collected critters, marine scientists immediately rinsed the gooey and translucent mess of life-forms from the filters into buckets of cold water to keep as many animals as possible alive for visual identification. Change in pressure is not a problem for most of these grazers, which can descend hundreds of meters deep during the day. At night they rise back up near the surface to feed, treading carefully near the thermocline, the distinct boundary between the deeper, colder water and the warmer surface water. A change in temperature from near freezing to bathtub-water warm can kill the temperature-sensitive creatures.
When the animals die, they turn opaque and lose color as their proteins and DNA break down. Most zooplankton species are known from samples collected less than 1,000 meters deep. During this expedition, the scientists started at the surface and continued collecting throughout the water column at every 1,000 meters of depth.
The expedition was unique in having taxonomists working over the microscopes side by side with the molecular biologists preparing the species for sequencing. "These historically nonoverlapping skill sets mean that organisms collected for identification often aren't preserved in a way that permits DNA extraction," says Rob Jennings, a postdoctoral fellow at the University of Connecticut. This expedition changed that. "Training scientists to be adept at both taxonomic identification and DNA-based analysis is one of the top goals" of the project, he adds.
By the time they returned to port on April 30, the scientists had catalogued 500 animals and genetically bar-coded 220 of them. By 2010 the Census of Marine Life scientists expect to have bar-coded all 6,800 known species of zooplankton and potentially that many as yet undiscovered species as well.