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Page 1 | Page 2 | Page 3 | Page 4 Deep Adaptations-->Now a professor of biological oceanography, Levin's interest in the deep sea was sparked when she was a graduate student at Scripps. She points to a deep-sea biology class taught by pioneering Scripps researcher Robert Hessler as the source of her enthusiasm. 
Levin has conducted research with one foot in shallow water and the other in the deep sea, concentrating in each environment on how animals adapt to highly stressful settings. Such extreme organisms have become Levin's research specialty. Her research has taken her to methane seeps, patchy areas found at depths of more than 7,800 meters (4.8 miles) below the ocean surface. Methane, a clear, highly combustible gas, resides in the earth's crust under the seafloor. When the planet's tectonic plates at certain locations shift, methane squeezes and "seeps" upward. Researchers first discovered animal communities living at such seeps in 1984 off Florida. New methane seeps are being discovered every few months, Levin says, and scientific understanding of their ecology is still in its infancy. Microbes at these sites consume methane and interact with bacteria to create a setting rich in sulfide, the "rotten egg"-smelling, typically toxic, chemical compound. Levin focuses on a family of sediment-dwelling polychaete worms (sometimes known as bristle worms) called Dorvilleidae and their survival mechanisms. 
"Because it's such a nasty setting, they don't have very many competitors," said Levin. "We've been able to track their different strategies, so they've been a really great model for studying adaptation to high stress in the deep sea." Levin's interest also covers enormous water masses that experience minimal circulation and, thus, extremely low oxygen levels. These areas are called hypoxic zones and can be up to 1,000 meters (3,200 feet) thick. Levin recently coauthored a study showing that oxygen-minimum zones cover 1.1 million square kilometers (680,000 square miles) of the deep ocean. One such zone exists off California at roughly 600 to 1,000 meters (2,000 to 3,200 feet) deep, part of a continuous zone that spans from Alaska to central Chile. Because such zones occur naturally, Levin says they have become an important comparative tool for studying human-produced "dead zones" created by pollution and ocean warming. The animals living in hypoxic zones employ a variety of strategies to make a living there, including those with specialized gills or tentacles to extract what little oxygen is available. The lack of oxygen prevents food decay, so those that are able to brave such conditions — certain polychaetes, for example — can find themselves stepping into an unchallenged feast. Mobile animals such as certain fish species can venture inside these zones for periods of time and repay their oxygen "debt" later in the day by swimming back to more oxygen-rich waters outside the low-oxygen zone. In addition, Levin studies chemosynthetic mud dwellers that convert chemicals into energy. By Levin's own description, this community features a host of "really strange organisms," including creatures that live in symbiotic, or mutually beneficial, arrangements. One extreme example is an oligochaete worm (related to earthworms) that lives with six types of symbiotic microbial organisms under its skin. Each microbe has a role to play, some synthesizing sulfide, others using it as an energy source, others converting nitrogen, and so on. "It's like having a worm with an entire ecosystem inside," said Levin. "We found it in .02 milliliters per liter of oxygen, which is about as low as you can measure." Next page: No Longer a Silent Deep |
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