Diversity of meiofauna at deep-sea hydrothermal vents and cold seeps with particular reference to nematodes

Abstract

Deep-sea hydrothermal vents and cold seeps are remarkable for their spectacular megaand
macrofauna, many of which appear to have a high level of endemism to these chemosynthetic
environments. It is not clear whether the patterns of biodiversity, faunal zonation
and biogeography documented in these size categories, are also present in the meiofauna.
This thesis examines the diversity and density patterns of the meiofauna (with particular
reference to nematodes) in quantitative samples collected from: Bathymodiolus mussel beds
in a deep-sea hydrothermal vent field on the East Pacific Rise; Bathymodiolus mussel beds
at an Atlantic methane seep site; an Atlantic hydrothermal vent sediment mound and a
reference non-chemosynthetic sediment site on the Mid-Atlantic Ridge. Results suggested
that deep-water chemosynthetic substrata will generally harbour assemblages exhibiting
lower diversity and elevated dominance. The densities of meiobenthos appeared to vary
in accordance with the presence of macrofauna. From the study of the meiobenthos of
hydrothermal vent mussel beds spanning 27 degrees of latitude on the EPR, the nematodes
share the same, if not a larger biogeographical province as the macrofauna. From
comparison of data collected from the vent mussel beds and the Atlantic methane seep
mussel bed, it was evident that the species composition of the nematode assemblage was
completely different. Density levels and major taxa composition were very similar as a
result of similar local factors acting within the mussel beds. Based on a comparison of
data collected from all mussel bed samples and the hydrothermal sediment core, it was
evident that the nematode assemblages were significantly different. Factors determining
all the observed differences are discussed.

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