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April 13th, 2003; Leg 4, Day #10

Today's update is provided by Amanda Bates, a Ph.D. student from the University of Victoria.

Site: 21N Clam Acres 

Apr13_clam_foot.jpg (54422 bytes)Today was an exciting day for many of the scientists on board because we launched the first dive of this expedition on the East Pacific Rise. The control room seats were full when we reached the seafloor, which was sparkling basalt. It is fun to think that we were looking at the newest part of our planet. The clean basalt was also a nice visual change from the mud bottom that we were exploring at Guaymas. We started the dive in search of Clam Acres, which is the rumored home of giant clams (Calyptogena magnifica) up to one foot long (see above). Although all eyes in the control room were keen to find serpulid worms and galatheid crabs, which are species that live just Apr13_mushroom_sponge.jpg (54592 bytes)outside vents and indicate that a vent is near, we were distracted by other interesting deep-sea species along the way. For example, we found a unique type of sponge that grows from a stalk and is shaped like a mushroom (see left). After three hours of exploration, we found Clam Acres, a diverse site with abundant clams and tubeworm (Riftia) bushes. 

Apr13_zoarcid_peeking.jpg (60360 bytes)


Many vent animals such as snails, crabs, and fish use tubeworm bushes as habitat. Can you find the zoarcid fish peeking out from the base of the tubeworm bush? We are interested in describing how the number of species found on tubeworm bushes varies with the size of the bush. 


Apr13_bumpy.jpg (63784 bytes)
Our first challenge is to identify the associated species that use tubeworm bushes as habitat. One method is to collect the tubeworm bush, bring it to the surface, and preserve all the animals on the tubeworms. The animals can then be examined with microscopes and photographed. Grabbing a tubeworm bush by the base and putting it in a secure box for transport to the surface may sound like a straightforward task. However, tubeworm bushes can be a struggle! It is difficult for the submersible pilots to find a spot where they can land and grab the bush securely at its base when the lava is as bumpy as it was today (see right). Only small tubeworm bushes can fit in the boxes on the submersible. Also, the worms often grow together and tangle and can be difficult to tease apart or remove from rock crevices. Faced with these challenges, we decided to be creative.

Apr13_limpets.jpg (55992 bytes)The species found on the East Pacific Rise are well described. Therefore, species can be identified from photographs. Luckily we have a high-resolution camera on the ROV, which we used to create close-up mosaics of the tubeworm bushes (see left). Although many species are missed using this technique because they are too small or occur inside of the bush, photography has many advantages. Taking photo mosaics is not as time consuming as taking a tubeworm grab. Therefore, more bushes can be examined in the precious bottom time we have in the vent habitat. Also, taking images is less invasive than removing many tubeworm grabs. This is the first time we have used photo mosaics to identify animals on tubeworms, and we are currently downloading the images from the camera. If we like the results, we plan to use this technique in the next two dives. Wish us luck! 

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