Aspects of certain exobiotic and endobiotic Audouinella spp. (Class Florideophyceae, division Rhodophyta)

Eleven exo- and endobiotic Audouinella species were investigated in this study. Isolates were obtained from supporting and 'host' material collected from sites in Scotland and Ireland. Taxa from the Culture Collection of Algae and Protozoa have also been studied for comparative purposes. For 6 of the endobiotic isolates identification at species level not possible -the field material often being of a few cells, and forms in culture, all obtained from single spore sources, showed significant morphological differences from one another. Evidence from some preliminary studies on cell wall structure and compositions indicate that the morphological differences observed are those of distinct entities, and comparative studies on cell wall histochemistry and fine structure are suggested as a possible taxonomic approach of value in distinguishing between Audouinella species. Calorific values of thalli seem to be linked with some aspects of cell wall structures. Sizes and positions of nuclei within cells may also prove features of taxonomic value. The nature of phycoerythrins proved not to be important. Endobionts from plant 'hosts' were able to effect penetration of substrata of animal nature (chitin, calcium carbonate). All endobionts appear able to penetrate agar substrata and filaments appear to 'digest' their way through the gel. The ability of endophytic species to penetrate animal substrates raises questions regarding 'host' specificity. Under various stress conditions there appear to be variety of morphological adaptations, e.g. hair formation, ball-like tufts of fragile filaments, reduction of size forms such as tufts with single filaments and spore production. Daylength appeared to affect different generations in terms of the tuft size and spore production. Night-breaks also were found to be relevant to vegetative growth and spore production, but has no effect on development of sexual phases. Spore release studies showed that these taxa possess an effective spore production mechanism with an effective liberation method which enhances dispersal in marine ecosystems. Spore output can be prodigious, with fertile plants producing a spore number many terms greater than their total cell complement. Photosynthetic rates studies showed that these plants are 'opportunists' taking advantage of any light available in the medium. The species can tolerate periods of darkness and still immediately commence photosynthesis when illuminated . In terms of light spectra they showed preference to the blue and green lights irrespective to the intensity. The Audouinella complex is composed of a wide range variety of species of different living habits. With endobiotic species only a few cells may be seen in nature. Culture studies combining morphological, physiological and histochemical methods may sometimes make contributions to solving the speciation problems in this genus