Mussel Bed is Dead
May 26, 2005
By Susan E. Humphris
Finding vent sites is not easy. Today, I went down to the seafloor in Alvin with pilot Gavin Eppard and pilot-in training Anthony Berry. Our mission was to find a vent site called Mussel Bed, located about 4.8 miles (8 kilometers) east of Rosebud and last visited in 1990. During today’s dive, all we had to find the vents was a position, some photographs, and a list of markers that had been left on the seafloor 15 years ago.
When we landed on the seafloor, Mark Spear, the surface controller on Atlantis, located our position and gave us a compass heading and distance to Mussel Bed. We set off across a bleak terrain of big pillow lavas lightly dusted in sediments. Our eyes were glued to the view ports, looking for signs of Mussel Bed.
When we reached the Mussel Bed location, we found nothing. This didn’t surprise us, because navigation was not as accurate in 1990 as it is today. It could be off by hundreds of meters.
Now, we were on our own to find the site using clues from our surroundings. We knew the Galapagos Rift runs west to east, so if we headed north or south, we would have to cross it. But which way should we go?
We turned north, but the increasing layer of sediment on the rocks told us we were moving away from active volcanic areas. We then turned south, past the given location of Mussel Bed, where the sediment decreased to a fine dusting and the rocks appeared broken up. Suddenly, we were on the edge of a cliff that plummeted down into a rift running west to east.
We descended slowly into the rift, cautiously working our way along it. In Alvin’s lights, we glimpsed something white between the rocks. Broken clamshells! Now we could use the abundance of shells to guide us towards Mussel Bed. Within minutes we found old markers and some rusting Alvin dive weights dropped on Alvin dive number 2,019 (that was 2,100 dives ago)!
Mussel Bed, named years ago for its vibrant community of mussels, was dead. As the heat source under the seafloor cooled, water stopped flowing through cracks in the seafloor. Without chemicals in the water needed to support vent life, mussels, clams and other organisms could not survive.
We photographed Mussel Bed, took samples of some of the old, sediment-covered shells, and departed.
“It’s likely that no one will ever go back,” biologist Tim Shank said. “Now we will search for new areas on the Galapagos Rift that may support life.”