Polysiphonia

Abstract: Twenty-six species of Polysiphonia are recognized from the coast of southern Australia. Their relationships are discussed, their distribution outlined and ecological notes are given. Characters found to be satisfactory for species delimitation include the number of pericentral cells. presence or absence and degree of cortication, whether or not rhizoids are cut off from the parent pericentral cells, the origin of lateral branches near apices (whether from the basal cell of trichoblasts or independent of them), the habit of the thallus, and dimensions and proportions of the thallus and segments of the branches. The presence and frequency of trichoblasts (or scar cells) may be characteristic but can vary with activity of growth of the thallus in some species. Cystocarps offer few characters, though the degree of enlargement of the ostiolar cells may be useful in some species. In male plants, satisfactory characters are whether the spermatangial branch replaces the whole trichoblast or only one basal furcation, and the presence or not of sterile apical cells. The form of the tetrasporangial branchlets and arrangement of tetrasporangia are often useful. Of the 26 species, 17 belong to subgenus Oligosiphonia and nine to subgenus Polysiphonia. Four species (P. scopulorum, P. subtilissima, P. sertularioides and P. brodiaei) are species of widespread distribution, the last-named possibly spread by shipping. One species (P. pungens) is known from the Pacific Coast of Canada and now from the State of Victoria. Some 17 species appear to be restricted to southern Australia, including I1 species newly described (P. haplodasyae, P. shepherdii, P. brevisegmenta, P. amphibolis, P.perriniae. P.propagulqera, P. australiensis, P. abscissoides, P. teges, P. constricta and P. adamsiae). Two species (P. decipiens, P. isogona) occur in southern Australia, New Zealand, and possibly subantarctic regions, while two others (P. abscissoides, P. adamsiae) occur both in New Zealand and in southern Tasmania. One species (P. haplodasyae) is a very small species apparently confined to its host Haplodasya. It appears that P. mollis has been recorded incorrectly from various other countries, and clearly much more critical study of the species of Polysiphonia is needed, especially of early species described from the Mediterranean and West Indies.

Abstract: The nature and seasonal extent of microbial fouling on Ascophyllum nodosum (L.) LeJol., Fucus vesiculosus L., Polysiphonia lanosa (L.) Tandy and Chondrus crispus Stackh. were observed by scanning electron microscopy. Bacterial filaments and smaller rod and coccoid forms dominated the fouling communities on all species, with pennate diatoms constituting a minor component in contrast to results with plastic substrates on which pennate diatoms dominated and preceded bacterial colonization. The total percent microbial coverage on the surfaces of all four seaweed species was determined by monthly stereological analyses of representative composite micrographs. These showed a simultaneous decline between April and May which could represent the die-off of the cold water bacterial flora when water temperature increased past the threshold for obligate psychrophiles. Microbial colonization patterns were directly correlated (P = 0.005) with maximum coverage in April and November–December and reduced levels from May to October. Significant inverse (P < 0.041) correlations between total percent coverage and water temperature indicate distinct seasonal cycles, however, the patterns of dominance by filamentous bacteria and rod and coccoid forms were markedly different. Total coverage patterns of both rhodophytes showed no apparent seasonal cycle and were not related to water temperature. Rod and coccoid bacteria were apparently suppressed year round on P. lanosa relative to the other species. These interspecific differences in seasonal fouling patterns are discussed in light of possible modes of regulation, especially algal antibiosis.