This paper explores the role of selective attraction to food in determ~ning the spatial (micro)distribution of closely related nematode species. The attractiveness of 3 different bacterial strains to 4 species of Monhysteridae, Diplolaimelloides rneyli. Diplolaimella dievengatensis, Monhystera sp. and Geomonhystera disjuncta, was studied in a multiple choice design. In our study area, the 4 nematode species considered are associated with Spartina anghca detritus decay and have partially overlapping microhabitat preferences. As they all belong to the same feeding guild, they are potential competitors for food. Each of the 4 nematode species was attracted to the bactenal strain B1, but important interspecific differences were noted in the nematodes' response to live or heat-killed bacteria, to bacteria at different cell densities or of different age, and to the filtered supernatant of B1 culture. While the responses of D. meylj to the Gram-positive bacteria Halobacillus trueperi and to the Gramnegative Eschenchia col1 \yere similar, D. dievengatensis and Monhystera sp. were preferentially attracted to H . trueperi and E. coli, respectively. This opposite preference influenced both the numbers and their relative abundances of D, dievengatensis and Monhystera sp. inside bacterial patches in experiments with a mixed 2-species nematode inoculum. Bacterial cell density strongly influenced the nematode response, \nth D. meyliinvariably preferring the highest cell densities offered, while D. dievengatensis and Monhystera sp. had a peak response at lower cell densities. Though chemotaxis IS suggested as an underlying mechanism, the nature of the nematodes' response remains unproved. The present results strongly support the importance of food patchiness in determining the heterogeneous distribution of nematodes, and extend the concept in such a way as to allow for small differences in mlcrohabitat choice between closely related species. They also support the view that nematodes are special~st feeders, though they probably select spots where suitable food is plentiful rather than individual food particles. Finally, the present study offers a baseline for an understanding and further study of patterns of succession among nematode specles associated with decaying Spartina anglica detritus in terms of highly specific relationships with different strains, growth stages, and densities of bacteria involved in the mineralization of Spartina anglica-derived organic matter.

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Enoploides longispiculosus and Adoncholaimus fuscus are representatives of nematode genera prominent in sediments of the North Sea and adjacent estuaries. Both are predatory nematodes, although predation is facultative in the latter. The present study investigates functional responses and prey selectivity in both species through the use of controlled laboratory experiments. Both predators had strongly prey density-dependent predation rates. A maximal predation rate of 4 monhysterid prey nematodes per predator per 24 h was found in E. longispiculosus at prey densities of 200 ind. per petri dish and higher; no such maximal predation rate was found for A. fuscus, indicating that this species was prey-limited at all prey densities tested. Predation rates were strongly affected by temperature, with a Q 10 close to 2 between 10 and 20°C. Incubation in the light resulted in a similar decrease in predation rate compared to dark incubations, as did a temperature decrease from 20 to 10°C. E. longispiculosus exhibited a clear preference for some nematode prey over others. An encounter probability model indicated that preferences could not be explained by encounter rates. Strike rates were low (<10%) in E. longispiculosus, and exceptionally low (<<1%) in A. fuscus, indicating that many encounters did not result in attack, or that a portion of the attacks did not result in prey capture. The observed predation rates cannot be supported by prey nematode standing stock and production at the 2 sampling sites used in this study, where E. longispiculosus dominates the nematode community in abundance and, especially, biomass. A. fuscus may mainly derive food from feeding modes other than predation; E. longispiculosus may be prey-limited in its natural habitat. Since this nematode also feeds on other metazoans, it may also impact temporary meiofauna. The high predation rates and prey selectivity of predacious nematodes may be important structuring factors to meiofaunal communities.

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A method for the separation of selenium-containing proteins and subsequent detection and quantification of selenium was developed. First, the proteins are fractionated by means of sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE); subsequently, the bands of the gel, containing the proteins, are analyzed by electrothermal vaporization (ETV)-ICP-MS to detect and quantify selenium. External standardization with the use of an internal reference (Te) was applied. A detection limit of ca. 40 pg Se per band and a recovery of ca. 98% were obtained. A single measurement is accomplished in less than 4 min and thus a gel lane after a separation of ca. 1.5 h, can be entirely analyzed with ETV-ICP-MS in 3.5 h. If limited to 10 bands, a gel lane is analyzed in 2 h (calibration included). The analysis is directly carried out on the stained gel, without blotting, which makes the analysis even more practical. This method was optimized using the selenoprotein glutathione peroxidase as model. Then, it was applied to the fractionation of proteins from a selenium-yeast candidate reference material. The reconstructed Se electropherograms are presented and compared with the stained gels. The major advantages of this method are the high resolution of the protein fractionation and the straightforward quantification of selenium