On Oscillatoria redekei Van Goor

Summary

Studies are reported of the seasonal distribution, growth in culture, transmission light microscopy and electron microscopy of a planktonic Oscillatoria c. 2 μm wide taken from St. James's Park Lake, London. The organism reached bloom densities throughout much of the survey period. The fastest apparent doubling rate in the field was 3.2 days, but in laboratory culture was 13 hours. In laboratory culture the organism proved to be very variable morphologically. Depending on the growth conditions used, it showed similarities with at least four different species in the taxonomic literature: O. redekei, O. planctonica, O. limnetica, O. obliqueacuminata. The name O. redekei is used here, as the forms usually found in the lake correspond best with the original description of this species. Structures that were some-times present, sometimes absent, included gas-vacuoles, sheath, terminal cells with pointed ends, structured granules and “additional” membranes near the cross-walls. The degree of gas-vacuolation was greatest at low light intensity (200 lux) and in old cultures. No factor other than light intensity could be found which influenced the degree of gas-vacuolation of cultures inoculated into fresh medium.