Volume 45, Issue 3

Intraplant variation in nuclear DNA content was quantified in DAPI-stained cells of Laminaria saccharina and Alaria esculenta . In both species, meristoderm, cortical and medullary cells were examined from vegetative fronds. In addition, DNA was quantified during sporogenesis, in free-swimming zoospores and gametophytes of A. esculenta . Zoospores and gametophytes had 1C (= N) levels of nuclear DNA in all cells, but vegetative cells of sporophytes varied from 2C to 16C. In A. esculenta nuclear DNA was significantly correlated with cell length, total cell volume and nuclear volume, whereas in Laminaria saccharina these correlations were not apparent. During sporogenesis of Alaria esculenta , maximal nuclear DNA levels of 8C were present in post-meiotic nuclei. During four subsequent mitotic divisions (to form 64 zoospores per sporangium at the 1C level) only one cycle of DNA synthesis occurred. These results show that mitosis can be independent of DNA synthesis in Laminariales, and that endopolyploidy is a generalized feature of multicellular plants.

A checklist of Moroccan marine brown algae, based on both literature records and some original data, is given. The distribution of each taxon for this region (12 Mediterranean and 27 Atlantic localities) is reported. Using present-day taxonomy, 131 species, infraspecific taxa and life-history phases are accepted for the Moroccan coasts.

Species of Amansia and Melanamansia from the tropical Pacific region have been re-examined, and compared with material from the Indian Ocean, Japan, Taiwan and the Philippines. All specimens examined from the Pacific region (except Hawaii and some from New Caledonia and Fiji) lack pseudo-pericentral cells, thus placing them in Amansia . Melanamansia glomerata is only reported from Hawaii, New Caledonia, Fiji, the Philippines, Vietnam, Malaysia and for the first time in the Indian Ocean from Kenya. Type material of Amansia rhodantha (Harvey) J. Agardh from Mauritius was compared and found not significantly different from the Pacific Amansia material (including type and isotype material of Amansia paloloensis South et Skelton from Samoa, which is reduced to synonymy), thus extending the distribution range of A. rhodantha as a pan-tropical entity.

In the present study we describe, throughout a single year, subtidal macroalgal assemblages present on a shallow platform and on a deep cliff, using species and functional groups as descriptors. The study site is located south of Leghorn in the north-western Mediterranean Sea. Univariate and multivariate analyses were performed to detect spatial and temporal variations.A total of 101 macroalgal species were found: 17 Chlorophyta, 13 Phaeophyta and 71 Rhodophyta. The shallow platform assemblage was more structured than that on the cliff, in fact the number of species was higher and a well developed stratified structure, consisting of turf, encrusting and erect vegetation layers was present. On the platform, functional groups showed qualitative and quantitative seasonal variations, while the cliff assemblage exhibited a dominance of crustose species throughout the year. The species richness found in the present study is lower than that observed in other Mediterranean macroalgal assemblages. This condition may be linked both to the spread of Womersleyella setacea turf, that may exclude other macroalgae by overgrow and pre-emption, and to the stress caused by sediment deposition and burial, that may damage macroalgal growth and recruitment. The multidimensional scaling analysis, performed both on the samples-species matrix and on the samples-functional groups matrix, showed a similar pattern, even if the use of species-level approach permitted a more accurate description of the assemblages.

The effect of ultraviolet (UV) radiation on ultrastructure, variable fluorescence of photosystem II and concentrations of photosynthetic pigments in the endemic Antarctic Rhodophyta Palmaria decipiens was studied. After 6 and 8 h of artificial UV-exposure a vesiculation of the chloroplast thylakoids and changes in the membrane structure of mitochondria were observed, which disappeared after 12 h of UV treatment. A 60% reduction of maximum quantum yield of photosynthesis (F v /F m ) was obtained after 4 h of UV-A+B exposure, which recovered up to 80% after 8 h in darkness and 10 h of white light. Exclusion of UV-B led to a minor reduction of F v /F m to 60% in the first 4 h of irradiation. The concentration of chlorophyll a increased after 4 h of UV exposure, whereas concentrations of phycoerythrin and phycocyanin decreased at the same time. After 12–16 h of UV exposure no significant changes compared to the control were detectable. These findings give an insight into the fine structural and physiological changes during and after UV exposure, and indicate an acclimation of the alga to UV radiation.

Phenolic compounds are an important component of brown algal cell walls. Physodes, packed full of phenolic compounds, accumulate in the peripheral cells and around the male and female conceptacles of Hormosira banksii . After periods of sun exposure, parts of the thallus appear dark brown (burnt). The brown layer consists of oxidised phenolic compounds that have been released from physodes in the peripheral cells. This brown layer only penetrates a few cells deep, thereby forming a protective layer for the photosynthetic tissue beneath. Physodes in the peripheral cells of H. banksii therefore appear to protect the plant from excess UV radiation. The physodes autofluoresce blue/blue-green under UV excitation, and provide a simple but accurate system of assessing phenolic location within the plant.

The city of Puerto Madryn, located within a section of Nuevo Gulf (Patagonia, Argentina) known as Nueva Bay, can be regarded as an important centre of anthropogenic impact. Intertidal assemblages of macroalgae were studied in order to test the hypothesis that the seaweed flora impacted by raw sewage would show significant differences in structure compared to that of control localities, mainly due to the increase in biomass of ephemeral and opportunist chlorophytes. Three rocky shores showing similar characteristics were selected. One of these was located near the sewage outfall of the city of Puerto Madryn. Two control shores were chosen approximately 30 km northward and southward of the latter. Four seasonal surveys were performed between June 1998 and April 1999. Biomass data of 35 macroalgal species were analysed by non-metric multidimensional scaling and the analysis of similarities permutation test. Species responsible for the differences between shores were identified by the similarity percentages routine. The macroalgal assemblage of the impacted site was significantly different from those of the two control shores throughout the year. Ulva rigida , Corallina officinalis and Ralfsia sp. were the species mostly responsible for these differences. Results indicate that the impacted shore showed signs consistent with an intermediate degree of eutrophication, particularly the increased abundance of the opportunist green alga Ulva rigida .

As part of a species richness survey and ecological investigation of intertidal epilithic cyanobacteria, samples were collected during winter (November 1998-March 1999) and summer (July-September 1999) from various rocky shores around Hong Kong. Morphological and ecological descriptions are provided for 15 species belonging to the genus Oscillatoria , namely Oscillatoria cf. annae , O. bonnemaisonii , O. cf. borneti , O. brevis , O. chalybea , O. cf. curviceps , O. cf. irrigua , O . cf. limosa , O. margaritifera , O. cf. obtusa , O. cf. ornata , O. cf. princeps , O. cf. proboscidea , O. cf. salina and O. sancta , all of which are new records for Hong Kong. Of these, eight species ( O. cf. annae , O. cf. borneti , O. cf. curviceps , O. cf. irrigua , O. cf. obtusa , O. cf. ornata , O. cf. proboscidea and O. cf. salina ) are reported for the first time as marine epiliths. Most of the species were restricted to the mid- and lower eulittoral shore and were found in the winter months.

Seasonal changes of benthic algal assemblages have been studied mainly in temperate and sub-tropical areas. It is not clear how natural processes contribute to the seasonal dynamics of algal assemblages on coral reefs, particularly in areas influenced by relatively cold upwelling waters. To investigate the seasonality in algal assemblages we monitored the percent cover of species and algal groups over one year (1994–1995) at two rocky-coral reefs at depths of 9–12 m on the Colombian Caribbean coast (Bahía Chengue, Tayrona National Natural Park, TNNP). The presence of relatively cold waters with temperatures of 25 °C and salinities of 36 ppt is indicative of upwelling events, while warm waters of 28–29 °C and salinities of 33 ppt indicate the rainy seasons in the area. The algal assemblage changed in composition and abundance throughout the year with a bimodal cover pattern observed for macroalgae and turf algae. During the rainy seasons (May to June and October to December) the assemblage was dominated by algal turfs (up to 43% cover) and showed low macroalgal cover (< 20%). In contrast, during the two upwelling periods (February and July to August) it was dominated by macroalgae (up to 44% cover). Cover of brown macroalgae Dictyota spp. (mainly D. bartayresiana ) declined from ≈34% during the upwelling to only 5% in the non-upwelling rainy seasons. Environmental data revealed a significant inverse correlation between water temperature and macroalgal cover, suggesting that increases in macroalgae are favoured by the presence of cold, upwelling events. It is likely that upwelling events bring nutrient rich waters that stimulate macroalgal growth, however, the role of nutrients regulating the abundance of macroalgae in the TNNP is yet to be investigated. The results of this study support the argument that benthic algal assemblages of coral reefs are a highly dynamic component of these ecosystems.

The vegetative and reproductive development of Polysiphonia lanosa (Linnaeus) Tandy (Rhodomelaceae, Rhodophyta) is reinvestigated based on material from the west coast of Ireland. This species is identified by the following unique combination of characters: a thallus consisting of 17–23 short pericentral cells; short and wide central axial cells; dichotomous branching; a complete absence of cortication; rhizoids generally remaining in contact with pericentral cells; and, its exclusive occurrence as a putative epiphyte of fucoids. Tetrasporangia are arranged in a spiral or sometimes a straight series and produced from the second pericentral cells with two presporangial cover cells. The spermatangial branches in P. lanosa are produced directly from each axial cell in the distal ends of erect branches and are not modified trichoblasts; vegetative trichoblasts are completely absent. The procarp has a four-celled carpogonial branch, as is typical for most members of the Rhodomelaceae, although species with either three- or four-celled carpogonial branches do occur in the genus Polysiphonia Greville. Although the genus Vertebrata S.F. Gray is available, is typified by, and has been used for this species, it is concluded that a molecular investigation is required to assess further the phylogenetic divergence indicated by these characters. The continued inclusion of Vertebrata in Polysiphonia is recommended until this work has been carried out.