Easter Microplate Expedition
April 3, 2005 Day 23
Please visit the ChEss website for additional information and translations in Español, Português, and Français.Last night was a rough transit SE across the Easter Microplate to this last dive site of the expedition. The good news, we made it in time to dive. The bad news, the dive was cancelled due to weather. The swells have been 3-4 meters (10-12 feet) and the trade winds are blowing hard. It is ironic that we had better conditions down at 38°S, near the roaring 40's. So today we dredged on the ridge axis and tonight we will run a multibeam sonar survey. Hopefully the wind will decrease tomorrow.
Right image: Dave, Kazumi and Jenny winching in the magnetometer we towed during the transit.
Left image: The nearly empty rock dredge. Right image: Nicole holding the one, lonely rock collected in the dredge: a small, glassy piece of a sheet flow.
Riftia pachyptila, the gutless giant hydrothermal vent tubeworm, was discovered in 1977 along the Galapagos Ridge along the East Pacific Rise. R. pachyptila is a wonderful animal that thrives in environments in which no one thought life could exist. The secret to their success is their symbiotic relationship with CO2-fixing, sulfide-oxidizing bacteria that live within a special region of the worm's body, called the trophosome (this unique internal organ can account for up to 50% of the worm!). The worm has no mouth or digestive tract, and completely depends on the bacteria for its nutrition.
Image on right: Greg photographing Ana removing eggs from the
Riftia tubeworm collected yesterday.
This animal is very important in that it was the first demonstration of this type of bacteria-marine invertebrate partnership. Since it's discovery, a number of other similar arrangements between bacteria and invertebrates have been discovered in a variety of habitats including vents, cold seeps, sewage outfalls, eelgrass beds, and anoxic basins. In fact, they may be more the norm, than the exception, in sulfide-rich environments. Many important studies have been conducted on the metabolic needs of both partners as well as the nutritional dialogue between them. For example, it is now known that the worm host has evolved many biochemical adaptations for symbiont accommodation, including effective mechanisms to concentrate inorganic carbon internally, sulfide acquisition from the environment using specialized hemoglobin molecules, as well as unprecedented pH and ion regulation. The symbiont, in turn, provides the host with organic carbon, which enables the worm to grow rapidly, quickly dominating communities around newly established hydrothermal vents. Although much progress has been made toward understanding basic biological processes enabling these organisms to tolerate sulfide-rich, oxygen-poor environments, many questions concerning the ecological physiology, diversity, biogeography, and community dynamics still remain. For these reasons we continue to study these fascinating animals.
Left image: Michel examining a Nematocarcinus shrimp through his magnifying loupe. Right image: Victor and Victoria, our microbiologists, in their new matching Atlantis t-shirts.
The ship's track since the beginning of the expedition. We are at the red star (26o 12' S latitude, 112o 36' W = 247o 24' E longitude). Tahiti is in the upper left and Easter Island, where we will arrive April 6, is at the extreme right.
All underwater photos were taken with the submersible Alvin, and are courtesy of Woods Hole Oceanographic Institution.