title: pH effect on the susceptibility to parasitoid infection in the marine diatomCoscinodiscusspp. (Bacillariophyceae).
abstract: The pH on the frustule of individual cells of the marine centric diatomsCoscinodiscus graniiandCoscinodiscus wailesii(Bacillariophyceae) was measured with pH microsensors in culture media with increasing pH values of 8.04, 8.14, and 8.22, respectively. In 85-96% of theC.graniicells the pH on the frustule was up to 0.4 units higher than that of the medium, reaching a maximum pH 8.95. Only in 2-3% the surface pH exceeded that of the medium by up to 0.7 pH units. These results strongly suggest that diatoms in batch cultures differ, at least temporarily, in their individual photosynthetic activities. Infection experiments with the parasitoid nanoflagellatePirsonia diadema(Stramenopile) showed that flagellates failed to infect when the culture pH was 8.8 and above. pH measurements on freshly infectedC. graniishowed that the prevalence of infection was higher in tendency on diatoms with low surface pH. Application of these results to parasitoid-diatom interactions in natural waters suggests that within phytoplankton populations a strong photosynthetic activity might prevent diatom cells temporarily from infection by pH-sensitive parasitoids.
authors.affiliation: Marine Botany (FB2), University of Bremen, PO Box 330 440, 28334 Bremen, Germany.
authors.forename: Stefanie F
authors.initials: SF
authors.lastname: Kühn
authors.affiliation: Max-Planck-Institute for Marine Microbiology, Celsiusstr. 1, 28359 Bremen, Germany.
authors.forename: Stephanie
authors.initials: S
authors.lastname: Köhler-Rink