Effects of Endolithic Parasitism on Invasive and Indigenous Mussels in a Variable Physical Environment

Biotic stress may operate in concert with physical environmental conditions to limit or facilitate invasion processes while altering competitive interactions between invaders and native species. Here, we examine how endolithic parasitism of an invasive and an indigenous mussel species acts in synergy with abiotic conditions of the habitat. Our results show that the invasive Mytilus galloprovincialis is more infested than the native Perna perna and this difference is probably due to the greater thickness of the protective outer-layer of the shell of the indigenous species. Higher abrasion due to waves on the open coast could account for dissimilarities in degree of infestation between bays and the more wave-exposed open coast. Also micro-scale variations of light affected the level of endolithic parasitism, which was more intense at non-shaded sites. The higher levels of endolithic parasitism in Mytilus mirrored greater mortality rates attributed to parasitism in this species. Condition index, attachment strength and shell strength of both species were negatively affected by the parasites suggesting an energy trade-off between the need to repair the damaged shell and the other physiological parameters. We suggest that, because it has a lower attachment strength and a thinner shell, the invasiveness of M. galloprovincialis will be limited at sun and wave exposed locations where endolithic activity, shell scouring and risk of dislodgement are high. These results underline the crucial role of physical environment in regulating biotic stress, and how these physical-biological interactions may explain site-to-site variability of competitive balances between invasive and indigenous species

Swelling isotherms of surfactant-responsive polymer gels

Recent progress in the study of surfactant-responsive polymer gels is reviewed. Polymer gels can be designed that drastically swell or shrink in response to small changes in the concentration of an ionic surfactant in an external bath containing the gel. The gel swelling isotherm, where the equilibrium gel volume is measured as a function of the external surfactant concentration, yields useful information on polymer-surfactant interactions. Associating and nonassociating polymer-surfactant pairs may be distinguished, and critical concentrations for surfactant binding can be determined. Generic swelling isotherms for different classes of systems have been established, which apply to chemically widely different gels (cellulose derivatives, vinyl polymers). Hydrophobicity and charge are the essential polymer parameters that determine the featur s of these isotherms. In order for a surfactant to associate to a nonionic polymer, the polymer hydrophobicity has to exceed a certain threshold. The required threshold hydrophobicity varies with the alkyl chain length, the headgroup, and the counterion of the surfactant. Added salt has large effects on all swelling isotherms

Mixed Systems of Hydrophobically Modified Polyelectrolytes: Controlling Rheology by Charge and Hydrophobe Stoichiometry and Interaction Strength

Rheology and phase separation were investigated for aqueous mixtures of two oppositely charged hydrophobically modified polyelectrolytes. The typical phase separation, normally seen for oppositely charged polymer mixtures, is dramatically reduced by the presence of hydrophobic modification, and phase separation is only detected close to the point of charge neutralization. While the two polyelectrolytes separately can give high viscosities and a gel-like behavior, a pronounced maximum in viscosity and storage modulus with the mixing ratio of the polyelectrolytes is observed; the maximum is located between the points of charge and hydrophobe stoichiometry and reflects a combination of hydrophobic and electrostatic association. Lowering the charge density of the anionic polymer leads to a strengthened association at first, but at lower charge densities there is a weakened association due to the onset of phase separation. The strength of the electrostatic interaction was modified by adding salt. Increased ionic strength can lead to phase separation and to increased or decreased viscosity depending on the polyelectrolyte mixing ratio

Association of a Hydrophobically Modified Polyelectrolyte and a Block Copolymer Followed by Fluorescence Techniques

By using absorption and fluorescence (steady-state and time-resolved) techniques, the interaction between a poly(acrylic acid) (PAA), randomly grafted with pyrene (Py) units (PAAMePy55), and a triblock copolymer of poly(ethylene oxide) and poly(propylene oxide) (EO20PO68EO20, P123) was investigated. From the fluorescence data, it is shown that upon addition of P123 a decrease of the (pyrene−pyrene, Py−Py) intramolecular association, i.e., a decrease of dynamic and static excimer formation, is observed. Time-resolved fluorescence data reveal the existence of two types of monomers (monomers that are able to form excimer, MAGRE, and isolated monomers) and two excimers. Addition of P123 causes also an increase of the amount of isolated Py monomers. The overall fluorescence data suggest that the PAAMePy55 and the P123 block copolymer associate strongly at low pH, leading to the formation of P123 micelles surrounded by one PAAMePy55 chain, where the pyrene groups are located at the PPO/PEO interface of the P123 micelles. Steady-state fluorescence results also showed that an excess of P123 micelles in solution is required for the association to occur. At high pH (pH 9 and above) the situation is less clear. The steady-state (particularly in the I1/I3 ratio) and time-resolved fluorescence results indicate a contact between the pyrene groups and PEO, which then would imply that there may be an interaction, but much weaker than at low pH

Ionic surfactants with polymeric counterions

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)This review summarizes recent progress in our understanding of aquoeus "complex salts" of ionic surfactants with polymeric counterions. Complex salts are simplified versions of the much-studied mixtures of oppositely charged polyelectrolytes and surfactants. and are also good model systems to study the fundamentals of polyion-mediated forces in colloidal systems. Comparisons are made with conventional ionic surfactants, which have monomeric counterions, and with surfactants having oligomeric counterions containing two, three or four charged groups. Complex salts form similar aggregates as conventional ionic surfactants, but as the degree of polymerization of the counterion increases, the interaction between the surfactant aggregates becomes attractive rather than repulsive. Introducing uncharged comonomers in the polyions affects both the shape and the organization of the surfactant aggregates. (C) 2008 Elsevier B.V. All rights reserved.147-48228236Swedish Research CouncilSwedish National Graduate School of Colloid and interface TechnologyFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

Three-phase separation in nonionic surfactant/hydrophobically modified polymer aqueous mixtures

Langmuir23209967-9973LANG