Description:
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A physonectid siphonophore,
<jats:italic>Nanomia bijuga</jats:italic>
, associated with a vertically migrating deep scattering layer, has been observed with a gas-filled float at depths in excess of 300 meters in the sea. This implies that gas is secreted and maintained in the pneumatophore against a diffusion gradient of 30 atmospheres or more. Analysis of the enclosed gases revealed concentrations of carbon monoxide exceeding 90 percent. Necessary voiding of this gas during a vertical ascent of 300 meters could give rise to a transient population of bubbles which would act as sound-reflecting targets.
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