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Our oceans; different worlds in the deep

AAAS member Lisa Levin has spent the last 25 years traveling across the globe looking at deep sea ecosystems. (Photo: Lisa Levin)

The majority of our planet is made up of oceans, but very little is known about what goes on in the deep. The world 200 meters to 11,000 meters below the surface is largely a mystery, and few people think about the impact these depths have on their lives. Scientists are beginning to discover that the deep sea, which is almost 90 percent of the oceans, holds immense diversity, which could someday provide the key to solving many of today's problems.

The continental margins, the areas where the continental shelf and its shallow waters meet the deep sea, are still largely a mystery to scientists. AAAS member Lisa Levin, director of the Center for Marine Biodiversity and Conservation and professor at the Scripps Institution of Oceanography at the University of California at San Diego, has been studying the oceans at the continental margins, and the rich diversity found there, for over 30 years.

"We believe the diversity is related to varied habitats," says Levin. "And those habitats are created in part by hydrographic diversity; there are different water masses with different oxygen, temperature, salinity, and pH properties. There is geologic diversity that includes varied topography, features like canyons and sea mounts. There is geochemical diversity created by different fluids seeping or venting from the Earth's interior, methane seeps and hydrothermal vents are examples of that. And then there are biological sources of diversity, there are massive reefs of deep-water corals, deep-water sponges, even dead whale carcasses create their own unique habitat. So all of those things come together on continental margins and contribute to the high biological diversity."

Check out this slideshow to see the beauty and wonder of life in the deep.

One interesting habitat found in the deep is oxygen minimum zones (OMZ). These are huge areas of water that have very little oxygen, making it challenging for life to survive. Oxygen minimum zones occur naturally, says Levin. They form in areas where there is upwelling, bringing nutrients to the surface, and stimulating large populations of phytoplankton. When this plankton dies and sinks, their decay uses up the oxygen in the water. If this occurs in areas with old water, that already is low in oxygen because it has been far from the surface for so long, and if there are no oxygen-rich currents entering into the area, then an OMZ forms, Levin explains.

"These habitats are so interesting because they represent some of the most extreme environments on earth," Levin says. "There are very low oxygen levels and we find organisms that have adapted to these. Sometimes they are morphological adaptations, sometimes they are physiological... Sometimes they are lifestyle adapted, and sometimes we just don't know how they manage. Some OMZ animals have evolved symbiotic microbes that live inside them and help them cope."

Many animals live at the edges of these low oxygen zones, just above their oxygen tolerance. Other organisms migrate in and out of the zones, feeding and using them for protection against predators during the day and rebuilding their oxygen at night. Other animals use special adaptations not found anywhere else to survive in these extreme environments.

"One of my favorites is an oligochaete worm, related to the earthworms in your garden," says Levin. "It has no mouth, gut or anus and has lost its digestive track. This worm has six different microbial forms that live under its cuticle that enable it to live, feed, remove waste, essentially do everything it needs to do. There is basically a whole ecosystem inside the worm. And they occur at very high densities at extraordinarily low oxygen levels."

Although oxygen minimum zones provided a habitat for unique creatures like these worms, they generally serve as a barrier for other types of life. However, with climate change, many scientists are worried these regions will grow. Warm water holds less oxygen than cold water, says Levin. Also some of the organisms that migrate in and out of oxygen minimum zones may have further to go in order to replenish their oxygen supply, because of expanding oxygen minimum zones and ocean acidification.


Despite the lack of scientific research, we are starting to use the deep oceans more. Oil and natural resource extraction already reach great depths. Fishing is a big problem for the groups of slow growing and easily depleted deep-sea species, says Levin. Mining is a new industry in the deep sea. And already waste pollutes the deep, both waste we purposely bury on the sea floor and waste on the ocean's surface that floats to the bottom.

"I think humans have to be able to take advantage of some of the economic opportunities that are out there, but we also have to do it responsibly and sustainably," Levin says. "There's a tendency for the scientist to always want to save everything and keep industry out, but I'm starting to realize that we are not going to be able to do that. We need to develop sustainable practices and learn how to make our [current] activities less destructive."

Levin worries the deep sea is largely "out of sight, out of mind" for most people. Their depths are so mysterious, and so far from our lives on land, that it is hard for many people to want to preserve the deep sea. Levin thinks the deep sea offers huge potential to humans, because it is so diverse and we have much more to learn about what's down there.

"The ocean holds a massive amount of genetic diversity and it's that diversity that's going to allow life to persist even though the climate changes," says Levin. "We need to work to preserve and conserve that diversity, even if we don't know the specific roles that species play right now or ways that they affect us. We must recognize that the genes in deep sea species are critical for adaptation and change."

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Rebecca Riffkin

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