2.4 MACROBIOLOGY

2.4a Biology of Low Temperature Sites - Maia Tsurumi and Jean Marcus

1. Introduction

This biology program focused on two major themes: 1. succession (continued colonization through senescence) of the South Rift Zone vents, and 2. The regional distribution of species and populations of Axial Seamount. An important aspect of our sampling is to couple our collections with vent fluid chemistry. We were very successful with this approach last year, and during NeMO 1999 we were fortunate to extend this coordinated sampling. Of all our samples, there were only three which had no chemistry data.

2. Succession

a) Continued colonization.

We were intrigued last year to find three types of initial colonization at new vents on the new lava. These included: i) Small vestimentiferan recruits with three or four other known species, ii) Dense snails and iii) A mix of scale worm species and other polychaetes. This year we anticipated more homogeneous communities with tube worm recruits at all new vents. This prediction mostly held true. Tube worms occurred at all vents with the exception of the northern area where venting may have subsided, based on the general lack of vent fauna. For example, we found no fauna at Milky vent, although it supported scale worms and other polychaetes last year. Although tube worms were present and of a morphotype typical of new venting, they were not found in the abundance that we anticipated. In fact, this scarcity of tube worms forced us to suction sample at many locations because grabs were not possible.

We were able to repeat sample at all locations where we had samples last year. Further, we were able to sample two new vents on the southern portion of the South Rift Zone. This sampling revealed a species of nemertean worm seen after the 1993 CoAxial eruption, but not observed on the Axial 1998 flow last year. Although the lava in this area is of uncertain age, the tube worm morphology indicates that this is new venting. Preliminary sorting of samples shows that new species have continued the colonization sequence. There also is an observed shift in the relative abundance and biomass of some of the species. Next year should be interesting...

b) Senescence

Since venting is ephemeral, we have the opportunity to see what the vent community looks like at all stages of its "lifecycle". This is next to impossible to do in many other ecosystems because of the time scales involved. Until recently, studies of vent succession have focused on the initial and intermediate stages of the communities. For the last couple of years our lab has been working on understanding the entire sequence of succession from initiation to death. This requires opportunistic sampling of dying or dead vents. We obtained video, a suction sample, and one tube worm grab at a senescent vent and anticipate that this will help us to sort out the final sequence of the vent cycle.

3. Regional Character

Axial Volcano is one of the few places on the Ridge that allows us to study discrete, well-separated communities. A current question in vent ecology is how populations interchange among sites. We are working on better describing species distributions in a regional setting. Some vent species are very patchy and we are attempting to understand in an ecological framework why this is. To understand vent community dynamics within the caldera, it is crucial to sample as many intra- and inter-vent field assemblages as possible. To this end, we re-sampled, CASM and most of the South Rift Zone (North and South). In addition, we have selected one species of polychaete for a population genetics study.

4. A Final Comment

We would like to thank the NeMO 1999 science party for their encouragement, help, and interest. Also a big thank you to all the crew of the Thomas G. Thompson and the C.S.S.F. ROPOS gang.

Macrobiological Sample List from Low Temperature Sites

SOUTH RIFT ZONE

Suction samples

· R483-1: Mkr 33, Suction for larvae over tube worms of R483-6

· R488-5: Mkr 33, Suction for C. Levesque and J. Marcus

· R488-6: Mkr 33, Suction for mat by C. Moyer, picked out large fauna

· R488-7: Mkr N8, Snail, Suction for fauna (some animals to C.Levesque)

· R488-14: Mkr N4 (Cloud), Suction for fauna

· R488-15: Mkr N4 (Cloud), Suction for mat by C. Moyer, picked out large fauna

· R488-16: Mkr N4 (Cloud), Suction for tube worms into flushing bottle

· R491-5: Mkr 33, Suction for gastropods ~ 3 m from crack (C.Levesque has most animals)

· R491-13: Nascent , Suction over tube worm bush for larvae

· R491-14: Nascent, Suction where tube worm grab was taken (C.Levesque has most animals)

· R492-1: Joystick, Suction because too few tube worms to grab

· R492-2/3: Joystick, Suction for mat and bag creatures by C. Moyer, picked out large fauna

· R495-16/17: Mkr 113, Suction for mat by C. Moyer, large fauna picked out

· R495-4: Non-vent, Suction on new lava for diatom mat

· R495-35: Crevice, Suction sample of old worms

Tube worm grabs

· R483-6: Mkr 33, area in front of Time Lapse Camera

· R491-16: Nascent, from spot where MTR (#4108) was and 3 other spots close by (some animals to C.Levesque)

· R491-18: Mkr N41, from spot where MTR (#4126) was

· R491-20: Old Flow, old worms on old lava

· R491-24: Oldworms, old worms on old lava

· R492-6: Coquilles, old worms on old lava

· R492-10: Bag City, large worms (up to 1 m), new vent?

· R496-3: Mkr 113, from top of pillar, where Moyer's microbial traps #20&21 were

· R501-17: Crevice, older worms from intermediate (?) lava

Animals from C. Moyer's microbial traps

· R483-3/7: Mkr 33, Animals from C. Moyer's microbial traps (#9&12)

· R496-1/2: Mkr 113, Animals from Moyer's microbial traps (#20&21)

CASM

· R497-9: base of T & S, where Vemco was recovered and MTR deployed

ASHES

· R502-15: Mkr I, suction sample for meiofauna and water chemistry

Water Chemistry

· Water samples from all sites listed above except Snail vent (mkr N8), Mkr N41, Old Flow and Crevice.

Time Lapse Camera

· TLC was retrieved and redeployed at Mkr 33. Tube worm grab from Marker 33 sampled the photographed area.