CD179: Deep-sea biology of the Portguese canyons


Daily diary

Wednesday 10 May 2006

Raquel writes:

"Today was the day we’ve all been waiting for. The SHRIMP team managed to fix the problems it’s been having the last few days and, not only did we finally get to deploy it twice today, we also obtained some of the best footage we’ve had so far!

The first run of the day was done this morning, traversing across Nazare Canyon at around 3500 m depth. SHRIMP landed on a flattish area just outside the thalweg, and abundant ophiuroids were observed. These are very pretty white brittle stars. Lots of bright orange shrimps and silvery fish were seen too. Then we descended down a very steep rocky slope which also had deep gullies between the rock outcrops, where sediment flows down the gradient. This environment was found to be the home of several soft corals and red anemones. We then continued into the thalweg. The thalweg is defined as the lowest-most point within a channel. At this depth, we were in the middle to lower section of the canyon, and the thalweg was starting to widen. Lots of uniformly spaced, straight-crested linear ripples were observed on this flat muddy surface, indicating strong bottom currents down the canyon which were causing the sediments to move into bedforms. The lack of many burrows here suggests that the ripples are currently active and the sea floor is too mobile for burrowing organisms to live in. When we reached the opposite flank, again there was a steep slope made of rock outcrops. This flank was different to the previous one, with mainly yellow stalked crinoids and small red anemones living here. Crinoids are animals that look like plants, with little “feet” at the bottom which hold on to the rock surface, a long thin body made up of stacked rings like a tube of Polos, and a spherical head and mouth at the top. Feathered “fingers” on the top help bring organic particles into the mouth. At the top of the steep rocky slope, we entered another flattish muddy area, again inhabited by abundant ophiuroids (brittle stars).

The second run of the day was done a bit further up the Nazare Canyon, between 600 and 1400 m. SHRIMP started off in a flat area, which displayed abundant sponges, anemones, spiky sea urchins and bright orange shrimps floating around. Then we went down a rocky slope which contained lots of sea urchins and brisingids - a type of multi-armed starfish, with either 7, 9, 11 or 13 arms. They were at least 30 cm across, reddish with thick arms. They looked more like a cross between an anemone and an octopus! And we got a good look at it because it accidentally got stuck to SHRIMP’s dangling weight and was carried for a while before falling off! Soon after this little incident, SHRIMP suffered a power failure and we had to haul it up to check what the problem was. Fortunately, it was a quick fix, and we could deploy it again a bit later on and continue the run from where we left it on the rocky slope. We continued to find more brisingids, sea cucumbers, anemones, sea urchins and starfish all the way across the traverse. The abundance and diversity of the fauna here was extraordinary, and the very subject of Abi’s PhD. She, of course, was ecstatic with the footage. All in all, two very successful and exciting (both biologically and geologically) SHRIMP runs!"


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April 2006
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