Today we completed 30 hours video survey of the North-East site. First we came to the cliffs and steep slopes. They were overgrown by sponges, hydroids and bryozoans. Especially beautiful were jungles of white stalked sponge Hyalonema. On a few occasions we saw large stalked crinoids, sea pens and gorgonian corals.
From the cliffs ISIS descended to the flat areas. We expected to find aggregations of small holothurians from the genus Peniagone as we caught thousands of them in the trawls during the 2007 ECOMAR cruise. We did find aggregations of holothurions but … not of Peniagone. It was a species from the same family but of another genus, they are much smaller and have transparent skin. In addition to the aggregations we did see many others holothurians. One of the most exiting was Peniagone longipapillata – a large red holothurian with very long thin papillae. This species was recently described from the MAR-ECO cruise on G.O. Sars and at the NE station it is the one of the most abundant species.
Another flat transect gave us another surprise. Instead of small holothurians we saw numerous echinoids from the families Urechinidae and Pourtalesiidae and their long narrow trails.
One of the most spectacular finding was meeting the dumbo octopus. First of all we observed a strange big purple cap sitting on the sea floor. When Isis began to approach the cap occasionally opened two big eyes and then started swimming flittering it’s ear-like fins.
Every time observing the sea floor we see many different animal trails. Most benthic and bentho-pelagic creatures leave their own characteristic traces. The champions of this bottom art are obviously the acorn worms creating ideally symmetrical spiral trails. Imagine trying to a perfectly spiral line in a dark room?
The deep-sea acorn worm or Enteropneusta are enigmatic animals belonged to the phylum Hemichordata, close relatives of vertebrates. Acorn worms are very fragile and are completely destroyed in trawls and other gears. That’s why they were almost completely unknown from the deep-sea until underwater photography and observation has appeared. The history of their exploration started in 1962 when US biologists Bourne and Heezen published a photo of an acorn worm creating large spiral coils on the sea floor. The creature was identified as an enteropneust worm. Later Danish zoologists Lemche with co-authors analyzed photo of enteropneusts from the deep-sea Pacific and found that they have tentacles around mouth like lophophoran animals. Because of that they established a new group of hemichordates Lophenteropneusta. Since that time acorn worms and their trails were repeatedly observed on the underwater records and photos but never collected. The enigma was partly solved by Nicholas Holland with co-authors who collected a specimen of a Lophenteropneusta using ROV Tiburon off the coast of California. They examined the specimen, found no tentacles on the collard and returned them back to Enteropneusta. However many question about their life are remain open. How do the acorn worms move from one site to another when finishing the spiral? Are they gliding over the bottom, swimming, borrowing or just eaten by fish?
Every ISIS dive brings us surprises and new knowledge and we are looking forward to learn more about the life in the deep sea.