Geographic variation in fitness-related traits of the bladderwrack Fucus vesiculosus along the Baltic Sea-North Sea salinity gradient

In the course of the ongoing global intensification and diversification of human pressures, the study of variation patterns of biological traits along environmental gradients can provide relevant information on the performance of species under shifting conditions. The pronounced salinity gradient, co-occurrence of multiple stressors, and accelerated rates of change make the Baltic Sea and its transition to North Sea a suitable region for this type of study. Focusing on the bladderwrack Fucus vesiculosus, one of the main foundation species on hard-bottoms of the Baltic Sea, we analyzed the phenotypic variation among populations occurring along 2,000 km of coasts subjected to salinities from 4 to >30 and a variety of other stressors. Morphological and biochemical traits, including palatability for grazers, were recorded at 20 stations along the Baltic Sea and four stations in the North Sea. We evaluated in a common modeling framework the relative contribution of multiple environmental drivers to the observed trait patterns. Salinity was the main and, in some cases, the only environmental driver of the geographic trait variation in F. vesiculosus. The decrease in salinity from North Sea to Baltic Sea stations was accompanied by a decline in thallus size, photosynthetic pigments, and energy storage compounds, and affected the interaction of the alga with herbivores and epibiota. For some traits, drivers that vary locally such as wave exposure, light availability or nutrient enrichment were also important. The strong genetic population structure in this macroalgae might play a role in the generation and maintenance of phenotypic patterns across geographic scales. In light of our results, the desalination process projected for the Baltic Sea could have detrimental impacts on F. vesiculosus in areas close to its tolerance limit, affecting ecosystem functions such as habitat formation, primary production, and food supply

Surface chemistry versus whole-cell extracts: antifouling tests with seaweed metabolites

Development of research in the field of chemical inhibition of colonisation of seaweed surfaces has been constrained by the lack of appropriate methods for testing realistic concentrations of potentially deterrent compounds. Here we extend earlier work (de Nys et al. 1998) on the red alga Delisea pulchra to 6 other Australian seaweed species to investigate whether these methods could be used more generally in studies of natural defences against biofouling. We compared the effects of surface extracts of D. pulchra, Caulerpa filiformis, Dictyopteris acrostichoides, Dilophus marginatus, Laurencia rigida, Solieria robusta and Pterocladia capillacea on the settlement of 2 ecologically relevant fouling species, and further compared the effects of surface extracts to those of non-polar, whole-cell extracts of the 7 seaweeds. We also measured the natural biofouling cover of these seaweeds in a field survey and examined whether levels of biofouling on the seaweeds in the field are predicted by the activity of either the surface extracts or the whole-cell extracts of these species. The results from settlement tests with surface extracts at natural concentrations showed that 2 species, D. pulchra and C. filiformis, had non-polar metabolites on their surfaces in sufficient quantities to significantly inhibit settlement. These species also had significantly lower biofouling cover in the field compared to the other seaweeds. The results of the settlement tests with whole-cell extracts, however, demonstrated that all the seaweeds contain non-polar metabolites that inhibit settlement at concentrations lower than total whole tissue content and that no individual whole-cell extract was generally more inhibitory than the others. Therefore, we conclude that results from settlement assays with whole-cell extracts are poor predictors of natural antifouling roles of seaweed metabolites, and that such bioassays are of little use if the objective is to explore the chemical mediation of interactions between seaweeds and fouling organisms. We also conclude, that with careful choice of solvent and extraction time, the surface extraction procedure described here may be broadly useful for investigating the deterrent effects of seaweed surface metabolites against fouling organisms

The influence of the atmosphere on the sintering of aluminum

Alloys of Al, Al-0.15Mg, and Al-12Sn made using air atomized aluminum powder and pressed to green densities of 75 to 98 pet were sintered under argon or nitrogen. Sintering in argon is only effective at high green densities when magnesium is present. In contrast, highly porous aluminum can be sintered in nitrogen without the need for magnesium. The oxygen concentration in the gas is reduced by the aluminum through a self-gettering process. The outer layers of the porous powder compact serve as a getter for the inner layers such that the oxygen partial pressure is reduced deep within the pore network. Aluminum nitride then forms, either by direct reaction with the metal or by reduction of the oxide layer, and sintering follows