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Observations of higher fungi and protists associated with the marine red algae Rhodoglossum affine and Gelidium coultri Phillips, Roger Edward


This dissertation reports a study of the fungi and 'protists' (Labyrinthulids, Thraustochytrids, Hyalochlorella marina) associated with the intertidal red algae Rhodoglossum affine and Gelidium coulteri. Research focused on laboratory isolations from algal thalli collected from in situ populations. Different isolation techniques and isolation media were employed to evaluate the abundance and diversity of fungi and protists associated with these red algae. Algal tissue surface sterilization and rigorous rinsing procedures were used to remove and/or enumerate surface-associated microbes. The results obtained from the different isolation techniques and algal tissue pretreatment procedures are compared and discussed in terms of their usefulness for each member of the algal-associated microbiota. Natural populations of affine and coulteri support a rich fauna of marine protists. The most prevalent members of this protist fauna were Labyrinthula spp. resembling the "Vishniac Strains" and Thraustochytrium motivum. Schizochytrium aggregatum, a new species of Labyrinthulid designated Labyrinthuloides sp. 1, and Hyalochlorella marina were also common depending upon the isolation method utilized. These protists appear to be associated with the surfaces of the algal thalli, and exist as saprobes and/or perthophytes rather than biotrophic parasites of the algal tissues. Isolations from field-collected algal tissues also yielded actinomycetes, yeasts, and a high diversity of imperfect fungi. Overall isolation frequencies for individual fungal taxa were low. Most of the mycelial fungi isolated are considered to be of terrestrial origin and of questionable 'significance' in the intertidal habitat. Only four, possibly five, are presently considered marine. The mycelial fungi most commonly isolated include: Acremonium sp. 019-78, Cladosporium cladosporioides, Dendryphiella salina, Penicillium spp., Phoma sp. (Group 1), Sigmoidea littoralis sp. nov., and Unidentified hyphomycete 044-78. Certain of these fungi may grow saprobically (as pertho-phytes) on reproductive and/or senescing algal tissues in the intertidal habitat, but their activities appear to be limited. Field-collected thalli of Rhodoglossum affine and Gelidium coulteri were allowed to decompose in mesh bags placed in the intertidal. The succession of higher fungi associated with the decomposing algae was followed by plating representative bimonthly subsamples of the algal tissues onto a Base Mineral Medium. Rhodoglossum affine deteriorated completely after 52 days of exposure, while a small amount of Gelidium coulteri remained after 71 days. Qualitative aspects of the mycobiota associated with the two algal species were similar, however fungi were isolated more frequently from coulteri. A dominant mycobiota was apparent after 36 days of exposure on the beach. Acremonium sp. 019-78, Dendryphiella salina and Sigmoidea littoralis sp. nov. were active colonizers of the decomposing algal tissues, and their isolation frequencies increased as decomposition proceeded. Several species of bacteria capable of utilizing the cell wall polysaccharides of red algae (agar, carrageenan) were also present on the decomposing algae. It is possible that the activities of these bacteria enhanced fungal development. Thraustochytrium motivum, Schizochytrium aggregatum and Ulkenia sp. RC02-80 were placed into sterile seawater cultures with surface-sterilized tissues of Rhodoglossum affine and Gelidium coulteri. After 72 hours of incubation, positive growth associations were examined using scanning electron microscopy. The three Thraustochytrids displayed luxuriant growth on all algal tissue types, and produced extensive ectoplasmic networks on the algal surfaces which functioned in attachment and, presumably, in the absorption of dissolved nutrients. Ectoplasmic net elements were resolved down to 0.02 pm in diameter, but no obvious 'penetration' of the algal tissues could be discerned. All of the protists (Labyrinthulids, Thraustochytrids, Hyalochlore11a marina) isolated from these red algae are described and illustrated. Certain commonly encountered and/or poorly known mycelial fungi are also described, including a new species of marine hyphomycete, Sigmoidea littoralis sp. nov.

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