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5. RESPONSE TO PERTURBATIONS
Recent observations of the biological consequences of seafloor volcanic eruptions
and the growth of hydrothermal sulphide chimneys and larger multi-chimney edifices
provide new insight into the ability of vent communities to colonise newly-created
habitat, to recover from major perturbations and to adapt to local-scale changes in habitat
conditions.
5.1 Seafloor eruptions
Information on the effects of eruptions on vent fauna comes from time series
observations at 9° 45’ – 9° 52’ N on the East Pacific Rise that followed the serendipitous
discovery of a very new lava flow, and from similar studies on the Juan de Fuca and
Gorda Ridges in the northeast Pacific. While the characteristics of the eruptions and the
suites of observations made vary between sites, the post-eruptive periods have a number
of consistent features that reveal the interconnection of magmatic, hydrothermal and
biological processes.
Seafloor eruptions provoke rapid and significant changes in the location and
style of venting. Widespread diffuse venting is usually observed soon after the event,
with new vents being created in areas where there was no previous venting 24. The
biological consequences of this perturbation of the hydrothermal system are
considerable. Existing vent communities can be destroyed by lava flows or as a result of
the re-organization of hydrothermal venting. Both the 9° N and Coaxial eruptions
initiated intense bursts of biological activity as organisms colonized new vents. Most
immediate were blooms of free-living microorganisms. The ubiquity of microorganisms
of most metabolic types in seawater and their ability to grow rapidly under favourable
conditions result in their being the first life forms to exploit the new energy source. In
the first few weeks after the eruptions, observers 24,25 reported the outpouring of
particulate microbial material from the subsurface through “snowblower” vents and the
massive accumulation of filamentous bacterial mats and flocculent microbial waste on
the seafloor in areas of diffuse flow. The discharge of biogenic particulates from
snowblower vents can be sustained for several months 24,25, suggesting continuous
microbial production in the subsurface. Post-eruptive diffuse venting can initially be
very widespread, supporting microbial growth over large areas of the seafloor. For
example, following the 1993 Coaxial eruption there was a 21 ha. Zone of microbial
growth on new lava flows 26.
Post-eruptive colonization or recolonisation by the vent fauna proceeds more
slowly than the microbial response because most recruits must arrive as larvae that settle
and grow into adult organisms. Some mobile predators and scavengers may recruit as
adults from nearby hydrothermal sites if they survive the eruption 25. Nevertheless, the
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