Microencapsulation As A Potential Control Technique Against Sabellid Worms In Abalone Culture

We have developed a novel application for lipid-walled microcapsules (LWMs) in the potential control of sabellid infestations in abalone aquaculture. The use of LWMs takes advantage of the filter-feeding nature of the worms, versus the herbivory of the host abalone. Initial observations indicated that the pest was capable of feeding on particles ranging from 3-30 mu m in size. Lipid-walled microcapsules were prepared using different combinations of lipids (tristearin, tripalmitin, and fish oil) to encapsulate water-based solutions. Feeding experiments using worm-infested shells indicated that in a relatively short time (30-60 min) most of the worms (80-95%) fed on the LWMs and that large numbers of LWMs were ingested. Fecal pellets containing LWMs were observed in the rectums of worms within 15-30 min. Feeding efficiency was examined using different concentrations of LWMs. The sabellid worm was an efficient feeder. At low particle densities (2.6 x 10(4) particles/mL), 66.7% of the worms had eaten modest levels of LWMs. An asymptote in particle density in relation to feeding occurred at 2.6 x 10(5) particles/mL, with 83% of the worms feeding on large numbers of particles. In separate observations, LWMs composed of tripalmitin and fish oil were observed in various stages of digestion in the stomach, rectum, and fecal pellets of the worms. Microcapsules were also observed in the digestive tract of mud worms, Polydora spp. that were also inhabiting abalone shell. The utility of LWMs for delivery of toxins to the sabellid pest holds much promise in ridding the industry of this nuisance species

Boundary layer method in the problem of far propagation of surface SV-waves

The SV polarized wave field is investigated in an elastic gradient layer of constant width. A point source is situated on the boundary of the layer. Rigid contact conditions are assumed to be valid on the boundary between the layer and an elastic half-space. It is shown that the interference field in the principal approximation far from the source does not depend on the relation between the phase velocity and the transversal and longitudinal velocities in the half-space