Even though the water now deep in the ocean won’t mingle with upper layers for hundreds of years, topside climate still drives the short-term booms and busts of bottom dwellers.
That’s the conclusion of a 14-year study of sea cucumbers, brittle stars, and other mobile bottom dwellers off the California coast, says Henry A. Ruhl of Scripps Institution of Oceanography in La Jolla, Calif. What links the top to the bottom is the fall of dead plankton and other debris that provides food in the depths, he and Kenneth L. Smith Jr., also of Scripps, say in the July 23 Science. They link changes in the abundance of certain species some 2.5 miles underwater to the El Niño and La Niña weather shifts between 1997 and 1999.
Marine scientists have discussed possible associations between year-by-year surface weather and deep-sea life. But “there are few actual examples in the modern ocean,” comments Andrew Gooday of the Southampton Oceanography Center in England.
“There has been a paradigm shift,” Gooday says. “If you go back 30 years, the idea was that the deep-ocean floor was very stable.” In the 1970s, though, biologists found evidence that even creatures living at great depths reproduce in accord with the surface seasons. As evidence has appeared for longer-term changes in deep-sea communities, marine scientists have come to see the ocean floor “as a more dynamic environment,” says Gooday.
Smith’s research team moored instruments at what they call Station M, a relatively flat spot, starting in 1989. About every 4 months, the researchers checked the instruments and collected samples of particles that had drifted into the depths. To monitor large, mobile residents, the team deployed an underwater camera along a line across the sea bottom.
Ruhl and Smith checked for correlations among the varying abundances of common species, the food supply wafting down to them, and the surface climate. They found that abundance of the food does change, lagging about 6 to 11 months behind peaks in surface-water phenomena related to El Niño. Changes in species abundance lag by additional months.
Some species, such as the sea cucumber Scotoplanes globosa, showed up only in small numbers in the camera surveys before the 1997–1999 El Niño and La Niña, but the species boomed in 2001 and 2002. In contrast, the sea cucumber relative Peniagone vitrea had been abundant during the early years of the new study but dwindled after the El Niño period.
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The findings dovetail with work at one of the few other long-term deep-ocean study sites: the Northeast Atlantic’s Porcupine Abyssal Plain, which the Southampton center has studied. There, a boom in a different sea cucumber, the Amperima rosea, correlates with a change in the nutritional quality of the food drifting from above, says Gooday.