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The abundance patterns of copepods on the Juan de Fuca Ridge was examined. One species was studied in detail. Twelve non-parasitic species are recorded from the Juan de Fuca, but only three dirivultid species and some unidentified harpacticoids are abundant in collections. Densities are estimated at 0·5 copepod cm−2 on vestimentiferan tubes to over 8 cm−2 on chimney surfaces. Aphotopontius forcipatus is most abundant at new vents and Benthoxynus spiculifer is most abundant at mature vents. Vents with reduced or undetectable fluid flow have higher diversity of copepod fauna.  The life cycle of the siphonostome Stygiopontius quadrispinosus begins with a centrolecithal egg brooded singly or doubly on the female. Hatching and naupliar stages are unknown in benthic samples. The preadult stage (copepodite V) recruits to the vent habitat. Pre-adult males attach to pre-adult females and fertilize at the final copepodite VI moult. As the sex ratio is highly skewed in favour of females, males probably inseminate many females and there may be mate competition in populations where males are rare. Reproduction is probably continuous or semi-continuous. Abundance is greatest on sulphide edifices near the points of hot water egress. This copepod co-occurs with the alvinellid polychaete Paralvinella sulfincola.

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