|South Atlantic cruise on "RV Akademik Ioffe" 2009|
31 October – 7 November, 2009
Author: Andrey Gebruk
The first SA MAR-ECO stations on this cruise were difficult for benthos sampling. The target area lies just north of the Romanche fracture zone which is characterized by very dramatic topography and sediment accumulation. The northern boundary of the target area is a very steep rise from the depths of the Sierra Leone abyssal plain to less than 1000m. Further south lies an even steeper slope, corresponding to the northern wall of the fracture zone. These steep, bathyal slopes are rocky outcrops, devoid of sediment. The only level, sediment-covered seafloor in this area is located at the very edge of the fracture zone’s northern wall; this flattened summit extends over 20 nautical miles in the E–W direction, but is only 1–2 miles wide, and the depths range from 1400 to 900m. We explored this summit with the ship’s echosounder and selected two transects for trawling, one in the deeper part, from 1400 to 1300m depth, and the second at the very summit, at a depth of 900m. Both trawls were successful and brought rich, spectacular seamount fauna, including various corals, including black corals (anthipatharians), sponges, large echinoids (Echinus sp.) and ophiuroids. The trawl at the summit brought a large number of large, jelly-like, pink holothurians (Paelopatides sp.), quite unusual for this kind of habitat. These holothurians indicate that the summit is covered with soft sediment, but attached sedentary forms were also numerous in this catch.
By the end of this week we also sampled the first locality in the southern part of the SEMS area, around 4°S, with depths of 2900-3200 metres. Long and tough trawling at these depths, at the uneven base of the underwater rise, has resulted in a slightly damaged trawl frame. The catch was rather small, but interesting, with especially numerous gastropods and bivalves, and also ophiuroids, polychaetes and small sponges. Interestingly, we also found a red holothurian in this catch, similar in appearance to the new species Peniagone longipapillata (recently described from the northern MAR based on MAR-ECO material). However, we will not be able to clarify the species name until we are back in our laboratories on-shore.