Thursday 1st July 2010

On the first day of the mid summer month the James Cook was on a transit, leaving behind the Mid-Atlantic Ridge and heading to Vigo, the port where our cruise will end up. Usually during a cruise, transit is a time of relaxation, but not when the cruise is about to end. Our thoughts these days are occupied with cruise reports and presentations for the final scientific meeting tomorrow. This is also the case with my own thoughts. I am reflecting  on the new species of holothurians we have collected or missed to collect but observed on the ROV dives. I study this taxon with Antonina Rogacheva who is also on board. I realised at some stage, it is a unique case having two experts on the same taxon of deep-sea invertebrates on board. Someone may feel that holothurians have received an excessive attention on this cruise, it can be true, but not because the two of us were determined to get more and more new specimens, rather because these animals are so abundant and often dominant in the deep-sea. So it was in our study areas. Among holothurians that were sampled using the ROV Isis on this cruise a number of species appeared to be new to science. These include one species of Ellipinion and one of Peniagone, both genera from the family Elpidiidae. It is not a surprise when finding new species in the deep-sea, unusual would be not discovering them. A big surprise was that both these species are among most abundant animals in the ECOMAR study areas. However, we were able to understand this only after many hours spent in the ROV control room surveying the seafloor. Also these animals are very delicate and gelatinous, almost like medusas. It means they easily can be overlooked in trawl catches simply because they disintegrate fast. Therefore, to collect these animals and to understand how important they are, one has to use equipment such as an ROV.

New species of Ellipinion at the seabed

New species of Peniagone at the seabed.

We also have collected several other species of holothurians that most likely are new to science. We shall be able to understand this only after proper microscopical studies back at our institute. The potential new species may occur among laetmogonid and synallactid holothurians that we collected. Those were regularly observed on a steep slope among or even on rocky outcrops –  a habitat not known as common for deep-sea holothurians. Again without the ROV we would never be able to sample such habitats.

Several other potential new species were seen during our video surveys but we did not find them on our collection dives. On the other hand, other species that looked unfamiliar to us, were escaping when we tried to collect them – they simply swam away. Swimming is an adaptation that gives obvious advantage to these animals in the environment of the mid-ocean ridge with a very rough topography, steep slopes and strong currents that can easily wash the animal away from the seabedf. We have learned on this cruise that swimming is much more common among deep-sea holothurians than thought before but this will be another story.

Andrey Gebruk

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