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Oases of Life in Perpetual Darkness: Seamounts are being destroyed faster than they are discovered
21 February 2010 12:34 am
A paper published on Feb. 19, 2010 in the Annual Review of Marine Science tells a story of discovery and destruction in a world hidden from human eyes, shrouded in eternal darkness
Jason Hall-Spencer points to a slide on the screen. What looks like a satellite image of the world with a picture of the Milky Way superimposed on it, is actually a representation of the world's ocean floor, studded with hundreds of tiny, bright dots. Each dot marks the position of a seamount, submerged pinnacles jutting up from the vast expanse of the abyssal plains.
Unless you are a deep-sea researcher like Hall-Spencer, chances are you have never seen a seamount nor will you ever catch a glimpse of one even from afar. Hidden deep below the waves, there is an alien topography of jutting mountains, most of them undersea volcanoes that are no longer active. Seamounts are sometimes clustered together but in most cases separated by vast and featureless stretches of deep ocean floor. They have been called biogeographic islands of the deep, their rugged peaks shrouded in perpetual darkness.
Unlike on land, where every peak, every mountain, every hill and every valley has been discovered, described and mapped, the deep ocean floor, which makes up the largest portion of the earth's crust, is mostly terra incognita. Exactly how many seamounts there are and where, nobody knows.
"We estimate there are fifty thousand or more seamounts out there," says Hall-Spencer, a lecturer at the University of Plymouth in the U.K and a member of the project CenSeam, a census exploring seamounts and the marine life associated with the newly discovered oases beneath the sea. "But less than 0.1 percent of them have been surveyed."
According to Hall-Spencer, the ecological processes driving life on seamounts still are poorly understood. Seamounts are veritable islands creating their own environmental conditions.
"Wherever we look at these undersea mountains, our sampling robots and nets bring up creatures we have never seen before. And the taxonomy experts who then examine the creatures in the lab have never seen most of them, either. It can take a year or more to describe a species never seen before, so we have a huge back log of all these organisms that are new to science."
Only problem: even faster than seamounts are being discovered, they are being destroyed, and with them entire ecosystems that we hardly know anything about.
Of the 235,000 plus marine animal species know to science, 98 percent live on the sea floor.
A big threat comes from destructive fishing practices. In the 1970s, fishing fleets struck unexpected riches below their hulls. Whenever they hauled their nets near the slopes of a seamount, chances were they came back on board bursting at the seams, spilling hundreds of tons of deep-sea fish across the deck. Because of their stark topography, seamounts attract large numbers and unusually diverse arrays of marine life.
"Some seamounts are so big that they divert ocean currents upward and send them swirling over the top," says Hall-Spencer. The resulting vortices trap plankton and other drifting organic matter and concentrate it on the mountain.
Deep-sea ecologists have only begun to catch a glimpse of the dazzling assemblages of creatures that inhabit the seamounts' slopes, nooks and crannies. Orange Roughy, for example, a big-eyed, sluggish, slow-growing species of deep ocean fish, come together in large numbers at seamounts to spawn. Their abundance, in turn, attracts other predators further up the food chain. Only one of the species going after Orange Roughy, though, obliterates virtually all other marine life in its path when pursuing its prey - Homo sapiens. Trawling nets, weighted down with steel balls and chains, lowered into the lightless depths and towed behind ships, scrape and scrawl paths of destruction into the flanks of seamounts.
"One trawl bulldozes deep-sea coral forests that took more than 4,000 years to grow in some cases," says Hall-Spencer. "Since most known seamounts are being trawled we have to ask ourselves whether the catches are worth the destruction of seamount habitats?"
His next slide, in the brief and factual language of science states what should give us the only necessary clue to find the answer: "Worldwide catches landed each year: 80 million tons. Estimated total seamounts catch (read: ALL seamount catches EVER MADE, taken together) 2 - 2.5 million tons, a fraction that seems meaningless in the big picture.
In addition to the clear-cutting in the ocean depths, seamounts and deep sea habitats in general, face another threat, one that is more global in nature, more sweeping, more unforgiving and deadly even if fishing practices become less destructive: ocean acidification. Carbon dioxide, spewn into the atmosphere by fossil fuel burning and swallowed by the oceans, causes seawater to turn more and more acidic. This drop in pH makes it harder and harder for some marine organisms - such as corals - to extract from seawater the carbonate they depend on to make their calcareous parts and shells.
Beneath the icy waters of the high arctic, Hall-Spencer and his co-workers found what did not exist according to textbooks at the time - a coral reef in the deep, thriving in the lightless chills of 5- 6 degrees Centigrade. Named Rost Reef, this unexpected deep-sea oasis stands 600 meters tall and stretches for 35 kilometers.
Because the reef lies at a depth shrouded in permanent darkness, its amazingly diverse fauna and flora entirely depend on "scraps falling off the table" - organic matter produced in the shallow waters above, where sunlight allows for photosynthesis and primary production.
"When the lights of our remotely operated deep sea submersibles lit up the darkness, we saw all these corals in bright colors of blue, pin and, red," says Hall-Spencer."
But when his team took measurements of pH values at various depths around the reef, a bleak picture emerged.
"Since 1770, when fossil fuel burning started, ocean waters around Rost Reef have become 30 more acidic. This magnificent reef has existed for about 8,000 years, and now that we have barely discovered it, our measurements suggest it is already headed for extinction."
What you can do to help protect seamount from further destruction: Don't consume or buy seafood that has been trawled from seamounts, such as Orange Roughy, Oreo, Grenadier, Cardinal Fish or Toothfish (Chilean Seabass).
To watch a video of the teeming life along the slopes of Davidson seamount, located 120 km Southwest of Monterey, California, one of the largest known seamounts in U.S. waters, go to: http://www.youtube.com/watch?v=5rb5HzR26OM
Reference: M. Clark et al.(2010) The Ecology of Seamounts: Structure, Function and Human Impacts, Annual Review of Marine Science 2010.2:253-278