by V eren a Tunnicliffe and Peter Linke
The account below considers the biota associated with bottom samples and camera observations.
Box Core SE of Axial Seamount 46° 05.2’ N /130° 10.0’ W 2.807 m (53 GKG) one burrowing anemone retrieved (Cerianthidae)
Disposition: P. Linke
The CASM Vent Field was sampled for biology in 1983 and 1986. Figure 68 is a representation of the fauna inhabiting the fissure in 1983. With the GTVA, we saw that much of this area was still active - if not expanded. A major biology objective is to determine if the site has accumulated species over the last 13 years or if it is in a steady state. The grab samples were insufficient to conclude but certainly indicate that the community has sustained itself.
CASM Vent Field (61 GTVA)
Sparse vent animals retrieved in remarkably good condition considering the collection technique. Interesting to note the high abundance of predaceous polychaetes among the bivalves: the same association (Calyptogena and Nereis, but different species) was evident in Lihir Seamount samples from the western Pacific. One limpet was recovered that previously was not recognize as a know Juan de Fuca vent inhabitant. The assemblage represents one of very low hydrothermal flow - but enough to support the symbionts in the clams.
Bivalve Calyptogena pacifica 15 live, 10 shells
Polychaete Nereis piscesae 10
Polychaete Hesiodeira(?) glabra 1
Polychaete Nicomache venticola 10
Snail Provanna variabilis 2
Limpet ?n. sp. 1
Tube worm Ridgeia piscesae 10
Amphipod unknown - possible contaminant 1 Disposition: V. Tunnicliffe
Fig. 68: Representation of the fauna inhabiting the main fissure (CASM ) in 1983.
CASM Vent Field (69 GTVA)
This grab sampled basalt and newly deposited sulfides. While the high-temperature venting may be very recent, the largest animals are at least 6 to 12 months old. Several animals were located under the basalts among the depositing sulfide. Some soft sulfides were already entombing worm tubes. The assemblage is indicative of a moderate temperature biotic habitat although two higher temperature species were present in low numbers. The association with sulfide deposition is curious and an intriguing dive target. Both the assemblage and the sulfide indicate a flow temperature not present in 1983 or 1986. Most animals were retrieved in fine condition and many were still alive four hours after delivery to the surface.
Tube worms Ridgeia piscesae 100’s
Limpets Lepetodrilus fucensis 1000’s
Palm worms Paralvinella palmiformis 100’s Pandora worms Paralvinella pandorae 100’s
Sulfide worms Paralvinella sulfincola Scale worms three species
Snails Depressigyra globulus
unsorted material
Disposition: V. Tunnicliffe
CoAxial Segment: Floe Site (83 EXPLOS)
Attempted to tow along the fissure over know active area with camera sled fitted with the SUAVE scanner. Weather conditions and resultant use of bow thruster on SONNE resulted in poor return on the navigation in the southern (Marker 26) area. Both long and ultra-short baseline systems improved in the northern (HDV) area and several passes were made with the camera over the vent target. While several markers and ALVIN dive weights were spotted, the small target of the vent area was not seen. Visual and SUAVE observations indicate that regional venting has not increased since the 1993 eruption. The fissure that previously had patchy signs of venting (1994) was virtually bereft of hydrothermal indicators.
The minuscule signature from the SUAVE even so close to HDV (within 30 m) suggests that this site likely diminished in effluent from 1995 observations.
CASM Site Axial Seamount (89 GTVA)
Grab of part of Lamphere Chimney - in vicinity of GTVA’s 61 and 69. This time the biological return was fairly small. The sulfide probably came from the lower, cooler flank of the chimney. Few high temperature animals were present and the tube worms retrieved were mostly thin, with lower haemoglobin (pale pink rather than red) and the organ with symbiotic bacteria was reduced. The few good tubeworm specimens were dissected for subsequent work on the ultrastructure of reproductive systems and frontal musculature. The alvinellid polychaetes were used in an attempt to culture thermophilic bacteria from the guts.
Tubeworms Ridgeia piscesae 20
Palmworms Paralvinella palmiformis 4
Sulphide worms Paralvinella sulfincola 8
Limpets Lepetodrilus fucensis 10’s
Scale worm Lepidonotopodium piscesae 1
Crab Paralomis verrilli 1
Disposition: V. Tunnicliffe
HDV Vent, Floe Site, CoAxial Segment (87 GTVA)
This grab was a failed attempt to sample biota at the vents formed in 1993 in conjunction with the new lava eruption. Navigation was excellent and the site was located within a half hour. However, in the pillow terrain, we did not grab the rocks. A tubeworm bush was
several 10’s 100’s half bucket
retrieved but lost from the top of the grab. To be successful, the basal substratum must return to the surface. W e did not redeploy for fear of damaging the site too greatly before the occasion of a possible ROPOS dive.
Second Accretionary Ridge, Oregon Margin, 600 m (109 GTVA)
Noted abrupt transition from dense population of sea urchins, sea stars and flatfish close to the “bioherm” summit to hard grounds mostly uncolonized by fauna (the rare gorgonian coral). I find this unusual given that local topography in this area tends to concentrate currents and augment suspension feeder populations. My guess is that the effluent from the mound is a major deterrent to colonization by the indigenous fauna. Between the blocky chunks of apparently indurated muds, we began seeing clam shells scattered on the surface.
Grabbed a relatively clear area but the amount of material retrieved was small. Consisted of heavily packed clays, some hardened chunks and clam shells. Most dead shells were still articulated and little dissolution was evident. Biologic material retrieved:
Live clams Calyptogena sp. about 45
Dead clams Calyptogena sp. about 100
Dead leather clams Solemya sp 6
Neogastropods two species (shells only) 4
Rag worm Nereis sp 1
Disposition: P. Linke
Calyptogena specimens were collected and stored alive in the cool room. An aquarium with ambient sediment and bottom water was prepared and some of the collected Calyptogena were placed here for cultivation experiments, which were started in the subsequent leg. The sediment seemed to contain a lot of H2S and had a greyish colour.
Summit of the Second Accretionary Ridge, Oregon Margin (110 GTVA)
Grab about 50 m from previous. Taken in terrain with large indurated sediment masses.
Grab closed on cable and most sediment and clams were lost. However, three large indurated masses were retrieved. Carbonate surfaces were irregular and pitted. The undersides represented a reducing environment. These chunks housed a specialized epifauna: some animals appear to be normal deep-sea but capable of coping with the ambient H2S while others - many on the undersides - are most likely seep indigenous.
Dead leather clams
from sediment Solemya
Chitons unknown & unusual
Sponges unknown
6
1 large, 2 sm.
3
Limpets seep endemic likely -2 0
Brittle stars unknown sp 3
Sea feathers unknown hydroids 5
Worms 3 spp. polychaetes 5
Scale worms seep endemic likely 3
Red blobs ?? Anthozoa 5
Disposition: P. Linke (some limpets to V. Tunnicliffe for DNA work).
Summit of the Second Accretionary Ridge (113 EXPLOS)
South to north profile through the centre of the elevation. The profile showed a prevailing southern bottom water current in the drifting particle. Ripple marks were visible on the more sediment-covered areas being a good indicator for strong bottom water currents.
Western Crest of “Bioherm” on Oregon Margin (115 GTVA)
Grab returned a couple hundred kilos of sediment and carbonate blocks and started degassing close to sea surface. Biological material included hundreds of live and dead clams and numerous other small species associated with vents. This material was not sorted but retained by Peter Linke for later use. Like 110 GTVA, of particular interest was the fauna associated with the carbonate blocks. Clams and snails were embedded in the lithifying matrix; a stiff mud overlayer was inhabited by live animals but the zone of accretion must slowly move outward enveloping some of these animals. Most noteworthy was a “golden slime” coating rock and sediment on the underside of the blocks. This organism is surely prokaryotic (maybe a slime mould?) and able to cope with this highly reducing habitat; gas bubbles were escaping while removing it from the clay layer. I believe this to be quite a novel beast worthy of close attention.
Disposition: P. Linke
Western Crest of “Bioherm” on Oregon Margin (116 GTVA)
Several deployments without luck, no sediment recovery. Several targets for later ROPOS dives were observed, but could not be sampled with the TV grab.
Western Crest of “Bioherm” on Oregon Margin (119 GTVA)
After 3. deployment a full grab with grey sediment was recovered, bubbles came out of it.
Those spots were sampled with sediment cores. The conduits had a more coarser apprearance with yellow and white crystals and grains. The sediment was very consolidated with almost no porewater in it, hence no much macrobiology. Some echinorid worms were recovered, whereas the stones were colonized by small vestimentiferans.
Western Crest of “Bioherm” on Oregon Margin (121 GTVA)
This grab recovered a dead community dominated by Calyptogena and numerous buccinid gastropods and small vestimentiferans. Obviously these organsims experienced a shut-down in the supply of seep fluids - there was no odor of H2S.
4.4.8 Microbiology