Underwater technicolor

Expedition to Davidson seamount finds strange paradise

A weird neon jungle cloaks the slopes of a drowned volacano 60 miles off the coast of Big Sur.

Crinkly pink gorgonians arch over fields of day-glo yellow sponges. Purple-petaled sea stars bloom against the crunchy clamshells underfoot, amid giant orange mushroom corals sprouting from gnarled black lava rock.

Humans saw this technicolor abundance for the first time this May during a Monterey Bay Aquarium Research Institute expedition to Davidson Seamount. A virtually unexplored underwater mountain that rears 9,000 feet out of the surrounding sea floor, the seamount is proving a treasure trove for geologists and biologists curious about Davidson's natural history.

Institute volcanologist David Clague led the May 6-15 expedition. He says he went to Davidson to explore the unusual geology.

"The typical undersea volcano is steep-sided, with a flat top and a collapsed center. These look like a series of ridges built atop each other," Clague said.

Davidson is the largest of a series of underwater volcanoes off California and Baja that show a similar geology—Gumdrop, Pioneer and Guide seamounts lie 40 miles west of the San Mateo shoreline, while Rodriguez, once an island, is located near Santa Barbara. These are the only seamounts in the world known to show this type of geology.

Clague used the remotely operated submersible Tiburon to take lava samples form Davidson's surface to see whether it was related to the formation of the San Andreas Fault, which is about 25 million years old in Northern California. The team gathered about 200 pounds of rock with each dive, which added up to about 1.5 tons by the time they headed back to shore.

A few of the samples puzzled scientists until put into historical perspective; a lump of coal turned out to have been dropped by a ship delivering fuel to the old Moss Landing power plant.

Even the samples that turned out to be part of Davidson carried some unexpected news. "We started out thinking they were probably the same age as the crust around them ... but they turned out to e surprisingly young," between 12-14 million years old, Clague said.

Because all of these odd-looking California seamounts are aligned northeast to southwest along a similar plane, and are of similar ages, they probably all originate from an ancient crack in the seabed. Clague suspects the San Gregorio fault twisted the earth's crust to move California farther east and the Pacific Ocean farther west.

Their unusual appearance probably stems from the way these seamounts formed.

"Most volcanoes gush out lava for hundreds of thousands of years," constantly leaking lava out their sides and eventually collapsing from the center, Clague said. But at Davidson and its relatives, "there were many small eruptions that happened 3-5 million years apart; a burp now and then." The lava ejected from explosion after explosion accumulated to form Davidson's 30-mile long pile of serrated peaks and ridges.

High peaks make Davidson an ideal home for the otherworldly collection of animals that crowds its precipitous slopes. Sponges the size of washing machines and 8-foot-tall sea fans crowd the ridge tops to strain bits of food from local currents.

"It's like flying through a forest; you really have to navigate amongst them," Clague said. Scientists believe these gorgonians to be hundreds of years old, growing slowly like giant sequoias on the ocean floor. The sturdy trunks of these invertebrate animals reached up to 8 inches in diameter.

The expedition even managed to snag a specimen gorgonian without killing it. "After seeing thousands of these things, we spotted one that had fallen over so recently that animals were still eating it," Clague said.

Biologists also saw a number of animals never seen before, including a clam with a shell so paper-thin, its pink interior could be seen from the outside, and a 3-foot diameter jellyfish only observed before on one other nearby seamount.

Clague says MBARI biologists are particularly intrigued by a fluorescent yellow sponge on which nothing else grew. They suspect the sponge may contain a toxin that could be useful as a human drug.

What makes it all the more astonishing is that Davidson's whole ecosystem thrives in utter darkness more than 4,000 feet beneath the surface, dependent on the dead plankton raining down from above to make a living.

"The seamounts are isolated habitats that are in a sense like small islands," said Jim Barry, a benthic ecologist with MBARI who studies sea floor animals.

Compared to the teeming zoo atop Davidson, the surrounding mudflats are empty wastelands occupied by only the occasional clam or lonely crab. Ecologists believe many of the same biological theories that apply on islands will turn out to be true for seamounts.

To reach both, colonizing animals need to survive long distance travels over inhospitable waters before reaching a good home, and millennia of a relatively isolated existence would allow life forms uniquely adapted to their homes to evolve on both types of formations.

Barry says that such island biogeography theories "have been considered for the seamounts, but no one has had the resources to explore those ideas thoroughly."

What is known is that seamounts tend to be oases of biological diversity in t he relatively empty stretches that typify the vast majority of the ocean floor.

Though they couldn't have known about the volcano, whalers used to hunt near the Pioneer seamount because they noticed the rich animal life in those waters. The reason for this abundance has to do with the way fluids flow around large bodies. The seamount's mass "interrupts the current and creates turbulence that mixes nutrient-rich waters up into the water column. That would improve the downstream productivity of the sea mounts," Barry said. The effect of the currents speeding past "is similar to standing at the edge of a tall building while the air roars right past you at the corner."

The huge volumes of water passing by also deliver unusually bountiful meals to seamount residents. "If your filtering net is in a slow current, the number of things you'll catch is low compared to an area where the current is intensified," Barry explained.

MBARI scientists are still combing through the specimens they've gathered, but booty from the Davidson expedition has already had major impacts. Videos taken during the voyage impressed officials at the National Oceanic and Atmospheric Administration so much that President Clinton declared the seamount a protected study area during MBARI president Marcia McNutt's June visit to the White House. The announcement could be a first step in adding the seamount to the Monterey Bay National Marine Sanctuary.

--Kathleen M. Wong