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Shank, T. M. 1 , D. J. Fornari2, G. Levai1, and R. A. Lutz1
1 Institute of Marine and Coastal Sciences, Rutgers University, New Brunswick, NJ 08903 USA
2 Dept. of Geol. and Geophys., Woods Hole Oceanographic Institution, Woods Hole, MA 02543 USA
Temporal and spatial variability in hydrothermal fluid temperature within an actively developing biological community have been successfully documented using time-lapse temperature probe arrays and time-lapse videography during a 10 month deployment at 9o 49.8'N on the East Pacific Rise crest. Using temperature as an indicator of cycles of venting activity, we have continuously measured (at various intervals) the frequency duration and relative strengths of hydrothermal cycles since December 1993 along a venting fissure at the Marker #141 site (2510m), a nascent hydrothermal vent area within the Biologic-Geologic Transect which was established in March 1992. This area has been extensively and increasingly colonized by vestimentiferan tube worms since April 1991 when the maximum fluid temperature was 29oC (ambient temp. 1.8oC). A Hi-8 video time-lapse system, and a linear array of 6 time-lapse temperature probes (arranged within the field of view of the video camera), each 9 cm long x 4 cm in diameter, spaced at intervals of ~10 cm, and capable of recording 1800 discrete temperature measurements (to within 0.5oC), were deployed in December 1993. Twenty seconds of video imagery were recorded once a day for the entire deployment, while discrete temperature measurements were obtained every 3.2 hours by the six temperature probes. Recovered temperature profiles from the 10 month deployment indicate marked short-term temporal variability (frequent 12oC increases between recording intervals) and spatial variability of temperature regimes (~14oC shifts within 10 cm between recording intervals). Spatial variation within the tube worm assemblage was demonstrated in August 1994 as one probe monitored temperature consistently between ~3oC and ~7oC and another probe 40 cm distant measured temperature increasing from ~3oC to ~22oC suggesting that transient and strong temperature gradients may develop with these microhabitats. Spectral analysis of individual temperature records supports the presence of a prominent ~12.5 hour tidal signature in the 9°o50'N area.
Video images illustrate dramatic short-term bursts of venting activity and a coincident increase in mobile megafauna, including brachyuran and galatheid crabs, zoarcid fish, and dense swarms of pardaliscid amphipods surrounding the vestimentiferan community. Recruitment was actively occurring and biomass was significantly increasing over time at this site. Vestimentiferan tube worms, Tevnia jerichonana (135 indiv.) with tube lengths up to 17 cm and Riftia pachyptila (30 indiv.) with tube lengths up to 25 cm, colonized the six-probe temperature array during the 10 month deployment. Other fauna attached to the recovered probes included lepidodrilid limpets (Lepidodrilus elvatus and alvinellid polychaetes (Paralvinella grassle).
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