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April 15th, 2003; Leg 4, Day #12

Today we dove again on Clam Acres at 21˚ N on the East Pacific Rise (EPR). 

As we rose from our bunks before dawn this morning, it became readily apparent that Mother Nature had decided to make some last minute alterations to our dive plans: winds blowing 30 knots which did not look like they would drop much throughout the day, and swells pitching this normally stable ship around quite a bit. This precluded the use of our elevator, which allows us to transfer larger loads back and forth to the seafloor. Because we have limited control of where the elevator winds up on the bottom after deployment and on the surface for recovery, the crew decided it was best to leave it on the fantail for today’s dive. We consulted with the crew and made some alterations to the sled on the front of the ROV, losing some of our open storage space and one of the water samplers but gaining an insulated bio-box, which we would need to transport animals alive back to the surface. Apr15_Misc.jpg (63455 bytes)

ROV Tiburon went in the water shortly before 7:00 a.m. and reached the seafloor around 8:30 a.m. We began the dive by heading toward the Homer (homing beacon) that we had left on our previous visit to Clam Acres on the 13th. Just to the south of the Homer, we found a

nice site for sampling and observation—medium-sized clumps of healthy looking tubeworms (Riftia pachyptilla), clams (Calyptogena magnifica) in the cracks and crevices, associated scaleworms, limpets, gastropods, and the eel-like zoarcid fish (see above). And everywhere we looked, hundreds and hundreds of white brachyuran crabs (Bythograea thermydron), which is a good thing, as collecting these crabs was one of the goals of the dive. 

Apr15_crabtrap.jpg (64307 bytes)As on the 13th, we deployed a crab trap baited with semi-fresh tuna guts and trimmings, putting it towards the base of a large Riftia clump. Within minutes, there was a line of crabs trying to get into the trap, and within one hour, when we went back to check on it, the trap was full, with upwards of 25 crabs in it. We collected the trap after it had been in place for three hours or so, and the final tally was 54 crabs in this one little trap (see left). This site has one of the densest crab populations we have ever seen. The crabs all made it to the surface alive, and as I write this, are still doing fine, although they are quite uncoordinated at surface pressures. The crabs will be going back to UC Santa Barbara with me for live-animal physiology experiments, which are part of my Ph.D. thesis. It should be an adventure getting them back through customs at LAX airport! 

Apr15_temp.jpg (54757 bytes)Another goal of the dive today was to sample discrete clumps of Riftia for quantitative ecology. Problem was, none of the clumps we found were small enough to be used for this purpose. An attempt was made to sub-sample a larger clump, but the tubes were all intertwined and did not allow the removal of a small piece. As a result, we got large clumps of tubeworms and the scientists had a long night of processing the worms for ecology and genetics. Suction sampling was Apr15_sample.jpg (67747 bytes)also done in and around the tubeworm clumps to try to find new species that often escape our notice. Additional work was done with a low temperature probe around promising tubeworm clumps (see above), where we tried to get an idea of the temperature gradient from the bottom of the clump to the top, which was in the range of 10 degrees Celsius at most of the clumps today. We also got a good water sample from the area right around the Riftia plumes, in the shimmering water that diffused up from beneath them (see left). 

Apr15_Kaylynn.jpg (46908 bytes)We found a new smoker today, just south of the Clam Acres area. It is a lovely little teapot smoker, so we named it “Kaylynn's Korner,” in honor of Kaylynn Dalpe, Bob Vrijenhoek's 20-month-old granddaughter (see right). It was just a baby smoker, about 5 feet high, that had grown up on a sulfide mound composed of materials from old smokers that had crumbled many years before. One of the MBARI pilots planted a pink flamingo next to the marker on the site. We all thought that Kaylynn would appreciate the artistic touch. 

Michael Henry

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