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Three different models were applied to study the reproduction, survival and dispersal of Mnemiopsis leidyi in the Scheldt estuaries and the southern North Sea: a high-resolution particle tracking model with passive particles, a low-resolution particle tracking model with a reproduction model coupled to a biogeochemical model, and a dynamic energy budget (DEB) model. The results of the models, each with its strengths and weaknesses, suggest the following conceptual situation: (i) the estuaries possess enough retention capability to keep an overwintering population, and enough exchange with coastal waters of the North Sea to seed offshore populations; (ii) M. leidyi can survive in the North Sea, and be transported over considerable distances, thus facilitating connectivity between coastal embayments; (iii) under current climatic conditions, M. leidyi may not be able to reproduce in large numbers in coastal and offshore waters of the North Sea, but this may change with global warming; however, this result is subject to substantial uncertainty. Further quantitative observational work is needed on the effects of temperature, salinity and food availability on reproduction and on mortality at different life stages to improve models such as used here.

Poly(ethylene glycol)-dextran (PEG-DEX) conjugates have been used as a combined stabilizer and surface modifier to produce resorbable poly(DL-lactide-co-glycolide) (PLG) microparticles by an emulsification/solvent evaporation technique. The use of PEG or dextran polymers alone was incapable of producing microparticles. Particle size measurements revealed smaller mean particle sizes (480 nm) and improved polydispersity when using a 1.2% PEG substituted conjugate relative to a 9% substituted material (680 nm). PLG microparticles modified by post-adsorbed PEG-DEX conjugates flocculated in 0.01 M salt solutions, whereas PLG microparticles prepared using PEG-DEX as a surfactant were stable in at least 0.5 M NaCl solutions. Surface modification of PLG microparticles was confirmed by zeta potential measurements and surface analysis using X-ray photoelectron spectroscopy. The presence of surface exposed dextran was confirmed by an immunological detection method using a dextran-specific antiserum in an enzyme-linked immunosorbent assay. The findings support a model in which the PEG component of the PEG-DEX conjugate provides an anchor to the microparticle surface while the dextran component extends from the particle surface to contribute a steric stabilization function. This approach offers opportunities for attaching hydrophilic species such as targeting moieties to biodegradable microparticles to improve the interaction of drug carriers and vaccines with specific tissue sites.