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Deep-Sea Hot Spots Harbor Abundant Life

John Roach
for National Geographic News
June 24, 2004
 
The deep ocean floor is a dark, cold, remote, and seemingly lifeless
place that until recently lay largely below the radar of science and
exploration. But with advances in technology, scientists are accessing
the deep and finding life everywhere they look.

"Typically the deep sea is very sparsely populated and at first glance it may appear as a vast, desolated plain of mud," said Jeffrey Drazen, a marine biologist with the Monterey Bay Aquarium Research Institute in Moss Landing, California.



Drazen is among the burgeoning class of scientists and explorers who are embracing modern technologies to probe deep beneath the ocean waters that cover 71 percent of the Earth's surface.

"But in every case where we have looked carefully, we have found an amazing diversity of animals that are specially adapted to this challenging environment," he said.

In some places, gases and mineral-enriched water seep from the seafloor and support vibrant communities of tube worms, clams, and other bacteria-feeding creatures. Current-swept nooks and crannies of underwater mountains resemble coral reefs.

Scientists refer to these areas as biological hot spots. They differ from the similarly termed geological hot spots, which are regions of high or continuous volcanic activity due to hot mantle material spewing into the planet's crust.

"Biological hotspots exist because environmental conditions come together at certain locations to make life very prolific," Drazen said.

Lauren Mullineaux is a marine biologist at the Woods Hole Oceanographic Institution in Massachusetts who studies biological hot spots that form on and around hydrothermal vents. She says ocean explorers do not happen upon hot spots unexpectedly.

"One identifies likely positions and does targeted searches," she said. "Hot spots typically differ in faunal [animal life] composition from other areas in the deep sea, so it is obvious when you have encountered one."

Hot Spots

The most well-known biological hot spots are hydrothermal vents, which spew black, mineral-enriched, scalding water from deep beneath the Earth's crust. In other areas, known as seeps, fluids and gases ooze up through the mud.

"Vents and seeps support chemoautotrophs [organisms such as bacteria that get their nourishment from inorganic compounds]," Mullineaux said. "So their faunas are not dependent on photosynthetic production from above, which can be very sparse by the time it gets to the deep sea."

The bacteria that live off the fluids and gases spewing and oozing at vents and seeps support critters that have a mutually beneficial relationship with bacteria, according to Drazen.

The relationship works because the bacteria actually take refuge inside the tube worms, clams, and mussels and convert the chemicals that come from the vents and seeps into food that the larger critters consume.

A third type of biological hot spot is found on underwater mountains known as seamounts. The seamounts are swept by currents, which bring a continuous supply of food to animals that can filter it from the water, such as sponges, anemones, and deep-sea corals.

"Photographs of the tops of seamounts look more similar to a coral reef than to the rest of the deep sea," Drazen said.

Seamount Protection

As the world's scientists have gained the technology to explore the deep-sea biological hot spots, so to have fishing fleets gained the technology to fish them. The orange roughy in particular has become a delicacy in the U.S.

According to the World Wildlife Fund, the U.S. imports an estimated 19 million pounds (8.6 million kilograms) of the fish each year, accounting for nearly 90 percent of the documented worldwide catch, 60 percent of which comes from the deep seas around New Zealand.

Orange roughy grow 12 to 16 inches (30 to 40 centimeters) long, weigh upward of 4.4 pounds (2 kilograms), and can live as long as 125 years. They gather on seamounts to spawn, where deep-sea trawlers drag their nets, harvesting several tons of fish per hour.

"As various fishing practices go, bottom trawling is a relatively destructive one," said Kim Davis, deputy director for the World Wildlife Fund's marine conservation program in Washington, D.C. "It is not selective and it excavates everything in its path."

The practice has decimated orange roughy populations and done untold damage to the fragile seamount ecosystems. According to Davis, scientific studies suggest that orange roughy will be commercially extinct within the next two decades.

To protect the fish and their habitat, the World Wildlife Fund is recommending that seamounts be protected as marine reserves. "Certainly at least until we figure out what is down there and what we will lose," Davis said.

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