PISCES 5 Dive 611
Vailulu’u Seamount Western Rift and Slope

The two main objectives of this dive were to establish two microbiological sampling stations on the outer flank of Vailulu’u Volcano and to conduct a preliminary survey of the megabenthic fauna on the Western Rift of the seamount. Two experimental sites were established, one at 1667 m in an area of diffuse hydrothermal venting and one at 1184 m. Each site had two microbial sampling chargers, a site marker and a temperature recording data logger. An additional data logger was deployed directly in a crevice with hydrothermal venting (as evidenced by schlieren, bacterial mats and an elevated temperature near the orifice of 8.1 degrees C). This data logger slipped into the crack and could not be readily recovered.

Brittle Stars feeding on Deep Sea Corals	Pillow Basalts on East Rift
[ Full Resolution Image ]	[ Full Resolution Image ]
Hiding the Temperature Probe Video [ 1.0 MB ]

During the up-slope transit, we observed a few additional areas of active venting and many sites where there had been venting in the past. Large and perfectly formed pillow lavas were present in most sites, with a few areas being dominated by broken talus fragments and some having completely black glassy pillows with no oxidation, apparent evidence for relatively recent formation. The topography was extremely rough, the slope being punctuated with numerous fissure systems and edifices of pillow lava. The epibenthic megafauna was relatively diverse and abundant between 1667 and 1500 m, and significantly less abundant and diverse between about 1500 and 1350 m. The fauna was dominated by Cnidaria (mostly octocorallian anthozoans), Hexactinellida (at least 3 species, probably more) and Echinodermata (stalked and comatulid crinoids, euryalid ophiuroids and asteroids). We observed and photographed two large eryonid crabs. Large stalked hexactinellids were common on vertical faces of large boulders. Three species of asteroids were observed, with most individuals being Hippasterias-type asteroids in the act of consuming gorgonians. A very large (70 cm) stalked crinoid was observed several times and a specimen was collected. Iridogorgia, including some very large specimens, were among the most common organisms on the entire slope. Euryalid ophiuroids were encountered only as epizooties on fleshy Paragorgia-like gorgonians.

Dive Information

Location: Vailulu’u Seamount Western Rift and Slope
Mission Date: Friday, April 1, 2005
Maximum Depth: 1670 m
Project Title: Bio-Hydro and Lithosphere interactions at Vailulu’u Seamount
Principal Investigators: Dr. Hubert Staudigel and Dr. Craig Young
Observer 1: Craig Young
Observer 2: Stan Hart