Settling rate and dispersal of sealworm eggs (Nematoda) determined using a revised protocol for myxozoan spores

Settling rates and densities of small bodies can be determined by recording settling rates in fluids of different densities, but similar viscosities, and applying Stoke's law. However, at low Reynolds numbers, drag effects reduce the object's settling rate and must be accounted for in sedimentation experiments. Using a revised protocol for spores of the myxozoan Henneguya doori that accounted for significant drag effects exerted by the experimental apparatus, we improve upon a previously described technique and apply it to eggs of the sealworm, Pseudoterranova decipiens. Sealworm eggs have a density of 1.08 x 10(3) kg/m3 and a characteristic Reynolds number of 6 x 10(-3). Fixed eggs settle in seawater at rate of 1.09 x 10(-4) m/sec, whereas fresh eggs settle at a rate of 1.01 x 10(-4) m/sec. Given reported current speeds on the Scotian Shelf off Nova Scotia, Canada, eggs would be transported approximately 50 km in 100 m of water in 12 days before sedimenting on the bottom. Eggs passed 1 m from the bottom would take about 3 hr to settle, and be transported 0.5 km. The size and density of sealworm eggs, and thus their resulting sedimentation rate, may have adaptive value in that they prevent excessive dispersion in space by strong oceanic currents.