Hydrothermal vents on mid-ocean ridges of the northeast Pacific Ocean are known to respond to seismic disturbances, with observed changes in vent temperature. But these disturbances resulted from submarine volcanic activity; until now, there have been no observations of the response of a vent system to non-magmatic, tectonic events. Here we report measurements of hydrothermal vent temperature from several vents on the Juan de Fuca ridge in June 1999, before, during and after an earthquake swarm of apparent tectonic origin. Vent fluid temperatures began to rise 4-11 days after the first earthquake. Following this initial increase, the vent temperatures oscillated for about a month before settling down to higher values. We also observed a tenfold increase in fluid output from the hydrothermal system over a period of at least 80 days, extending along the entire ridge segment. Such a large, segment-wide thermal response to relatively modest tectonic activity is surprising, and raises questions about the sources of excess heat and fluid, and the possible effect on vent biological communities.

To investigate food web structure in diffuse flow vent environments, an entire macrofaunal community associated with a single aggregation of the tubeworm Ridgeia piscesae was collected from a vent field on the Juan de Fuca Ridge in the NE Pacific. All members of the community were identified and enumerated, and the biomass and stable carbon (δ 13 C) and nitrogen (δ 15 N) isotope ratios were determined for almost all taxa. Symbiont-bearing invertebrates (primarily R. piscesae) accounted for a vast majority of the biomass of the community, and 3 presumably grazing bacterivorous gastropods dominated the biomass of the consumer fauna. Biomass and abundance of individuals declined from the bacterivore to the scavenger/detritivore to the predator feeding guild. Several species (a folliculinid ciliate, Idas washingtonia, Provanna variabilis) possessed unique stable isotope signatures, suggesting the possibility of symbiotic relationships with autotrophic bacteria. Stable isotope values varied widely between and occasionally within species in the lowest consumer levels suggesting a great diversity of food source 13 C and 15 N composition. Based on the distinct isotopic values of 3 bacterivores, 3 potential pools of isotopically-distinct microbial production were identified. The 4 highest-biomass predatory species (all polynoids) possessed δ 13 C and δ 15 N values consistent with a diet that included the tubeworm R. piscesae, a species comprising 83% of the total biomass in the collection, and the gastropod Depressigyra globulus, a species comprising 10% of the total biomass in the collection. A potential specialist predator (Clypeosectus curvus) on folliculinid ciliates was also identified. Overall the study suggested a dominant pattern of energy transfer from microbial producers to symbiont-bearing siboglinid tubeworms, various bacterivores (gastropods, polychaetes and pycnogonids), and detritivorous polychaetes to predaceous polynoids.

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Yearly, in siru growth of two species of cold-seep vestimentiferan tubeworms was measured using a combination of banding and video analysis. A total of 53 animals from 15 different aggregations were included in the study, which was conducted over a Cyear period. The most common species, Lamellibrachiu sp., grows very slowly (averaging 0.77 cm . a-') and yet commonly reaches lengths over 2 m. Based on conservative calculations we conclude that individuals in mature aggregations are a minimum of 100 a old and are likely to be much older. Smaller numbers of a second species of vestimentiferan (related to escarpids) were also monitored over this period. We consider it likely that the individuals of the second species banded for this study were already on the plateau of their growth curve, and that the very low average growth rates recorded here would lead to an overestimate of the ages of the individuals used in this study. However, life history considerations combined with the extremely low measured growth rates of this species suggest it is also long-lived.