A diary of the first ECOMAR cruise to the Mid-Atlantic Ridge
July 23, 2007
Filed under: Uncategorized — Nikki @ 5:35 pm

trawl sample

On Monday we sampled the benthic megafauna using the Semi-Ballon Otter trawl (OTSB) (see diary entry for 21/07/07). This was the second trawl station at the South Eastern station. The sampling was quite successful. Many phyla were represented. In terms of abundance and wet weight holothurians; fish, porcellanasterid, pterasterid and brisingid starfishes, madreporarian corals and alcyonarians dominated. The other groups in the catch were pennatularians, decapod crustaceans, barnacles, sponges, hydroids, polychaetes, pycnogonids and others. Many specimens were in very good condition.

At least 16 holothurian species were recognised, the group of organisms I am particularly interested in. The most abundant were Abyssocucumis abyssorum, Benthodytes sp., Amperima rosea, two species of Peniagone and Molpadia, Bathyplotes sp. Some of the holothurian species are probably new to science. One of dominant species, the holothurian Amperima rosea, is known as an opportunistic species which responds to episodic fluxes of organic matter. The catch was also notable for the number of fish, especially Halosauropsis macrochir and Coryphaenoides brevibarbis.

The fauna was sorted to the lowest reasonable taxonomical level. Samples were preserved in 4% buffered formaldehyde. Selected specimens were fixed in absolute alcohol for genetic studies.

anthomastus Holothurian

Following this trawl, an echo-sounder transect was carried out to examine the zooplankton. We then carried out the second Megacorer deployment at this station, which returned 6 perfect cores. One of these contained an individual of the holothurian Kolga nana, the second opportunistic species that we have found at this site. Due to worsening sea conditions, we were not able to deploy the OTSB again this evening, so work proceeded with a series of CTD deployments.

Antonina Rogacheva
P.P. Shirshov Institute of Oceanology
Moscow, Russia