Based on light and electron microscopical investigations, a new genus Craspedostauros is described for a group of marine biraphid diatoms previously placed in Stauroneis Ehrenberg. The genus Stauronella Mereschkowsky had been erected for one of these species, Amphiprora constricta sensu W. Smith, but Mereschkowsky's name cannot be used for nomenclatural reasons. Craspedostauros species can be recognized by the possession of cribrate areolae, a stauros that is usually narrower than the fascia, many girdle bands with double rows of cribrate areolae and two chloroplasts, fore and aft of the central cytoplasm, each with a central pyrenoid. The genus shows similarities in its pore structure and chloroplast type and arrangement to Mastogloia Thwaites ex W. Smith and Aneumastus Mann & Stickle, suggesting that it is more closely related to these than to other naviculoid genera with a stauros, i.e. Stauroneis, Staurophora Mereschkowsky, Meuniera Silva and Haslea Simonsen. The stauros is a feature that probably arose a number of times. A description of the genus and its currently recognized members is given, with a key to their identification. Four new species are described, the types of which have been deposited in the Natural History Museum, London. The status of Stauronella constricta var. linearis Mereschkowsky remains unclear in the absence of any material from the Black Sea. Some marine stauroneid diatoms that do not belong in Craspedostauros are briefly discussed.

The diversity and abundance of terrestrial, lithophytic cyanobacteria in tropical biomes and the variety of rock habitats which they occupy are discussed. The following results are presented in detail. Exposed rock surfaces on different continents and under different climatic conditions are occupied by a cosmopolitan, well-adapted, low-diversity microbial community dominated by cyanobacteria and cyanobacterial lichens. For inselbergs (isolated rock outcrops) in dry savanna, the ratio of rock covered by lichens to that covered by free cyanobacteria is approximately 5:3. In humid savannas this ratio is approximately 1:26, and in rainforests there are hardly any lichens on rocks. The primary production of epilithic communities, expressed as CO2 fixed calculated from chlorophyll a, can reach an annual 27 g m−2. When calculated for a hypothetical inselberg, production values for very dry thorn bush savanna, dry savanna and humid savanna are 1:3·2:4·2 on the basis of the entire inselberg, and 1:3·2:1·4 when calculated on a square metre basis (due to a larger area covered but lower productivity in the humid savanna). Biofilm communities are important in biogenic weathering and they enrich the soils surrounding the rocks with nitrogen.

Two brown algae, Pelvetia canaliculata and Laminaria saccharina, from the higher and lower mediolittoral belts respectively, have been tested for their capacity to overcome high-light stress in water and in air (in both fully hydrated and desiccated states). When exposed to supersaturating light irradiance in water, the two species developed non-photochemical quenching of fluorescence (NPQ) which was correlated with an increase in the de-epoxidation ratio (DR) of the xanthophyll cycle carotenoids (violaxanthin, antheraxanthin and zeaxanthin) and was followed by a slower decrease in oxygen evolution. NPQ reached values of up to 9 in P. canaliculata but only 4·5 in L. saccharina, at DRs of 0·65 and 0·5, respectively. In air, the xanthophyll cycle was also operative but the efficiency of de-epoxidation decreased linearly with the degree of hydration of the thallus. Photoprotection capacities in air also appeared higher in P. canaliculata than in L. saccharina, probably due to the higher molar content of the xanthophyll cycle pool size relative to chlorophyll a (Chl a) in the former (nearly double of that L. saccharina at 19 carotenoid molecules per 100 Chl a), which may be associated with a higher DR at the same level of desiccation. The concomitant higher accumulation of zeaxanthin in P. canaliculata might divert a higher percentage of the incident energy from the reaction centres, as demonstrated by the levels of NPQ, with steady-state fluorescence reduced to below the initial F0 level. Such differences, together with the unequal resistance to desiccation of the operation of the xanthophyll cycle, should be considered as possible factors responsible for the distribution for these two species on the shore.

The elemental composition of cells of Anabaena flos-aquae was investigated by energy-dispersive electron probe X-ray microanalysis (10 kV) of mixed phytoplankton samples obtained from different depths within a stratified eutrophic freshwater lake. Preliminary studies had indicated that at 10 kV, X-ray information was derived mainly from the peripheral region (up to 1–2 μm) of cells. Routinely detectable elements (present in at least 50% of cells) included Mg (overall mean 112 mmol kg−1 dry mass), Si (1850), P(313), S (113), Cl (92), K (300) and Ca (56). Peaks of Na and Al were also frequently present. Individual elements showed a wide range of intracellular concentrations at each depth within the lake. Si had a clear bimodal distribution at depths of 1–8 m, indicating both low-Si (mean concentrations 54–290 mmol Si kg−1) and high-Si (2770–3800 mmol Si kg−1) cell subpopulations. Low-Si cells had significantly higher concentrations of other detectable elements compared with high-Si cells, but could not be distinguished from the latter in terms of morphology or stage of cell cycle (comparison of dividing and non-dividing cells). High-Si cells were intermixed with low-Si cells in individual Anabaena colonies and decreased proportionally with depth, ranging from approximately 75% in the surface sample to 10% at 8 m. With the exception of Si, mean elemental concentrations of Anabaena populations were closely similar throughout the epilimnion. These differed from the metalimnion sample, which had significantly higher concentrations of Mg, P, S and K, and a lower concentration of Si. Mean ratios of certain elements (Mg, P, S and K) and ion groups (monovalent/divalent cations) were highly constant throughout the sampled water column. At each depth, most of the cell elements were significantly and positively inter-correlated (Pearson analysis), with Mg, P, S and K typically constituting the major group (factor analysis). Correlations with Si were invariably negative, suggesting a separate (possibly cell wall) location of this element in the cell.

Two 13·1 m2 ponds at Auchincruive, Scotland, were used to treat the diluted liquid phase of separated piggery slurry, in order to identify the climatic and pond operational parameters which influence biomass production and nutrient removal in these systems at a constant areal loading rate. The ponds were operated from April to November at 0·12, 0·24 and 0·34 m depth as batch-fed reactors. Average 5-day biochemical oxygen demand (BOD5) loading was 6·24 g m−2 d−1 and the ponds were mixed at a mean surface velocity of 0·20 m s−1. Dry matter, chlorophyll, optical density (OD560), NO3, NO2, NH4, urea and total phosphorus were determined daily. Temperature, pH, dissolved oxygen and incident irradiance were monitored continuously. Correlation and multiple regression analyses were used to determine significant interactions between environmental factors, biomass production and nutrient removal. Both chlorophyll a and optical density were accurate predictors of dry matter biomass. All measures of pond biomass were positively correlated with elapsed time, surface daily irradiance, daylength and pH, but negatively correlated with pond depth. Significant correlations between pH and daily irradiance, maximum dissolved oxygen and forms of nitrogen (nitrite or nitrate) suggested that the final pond pH represents an equilibrium between alkalization by photosynthesis and acidification by nitrification. Total nitrogen removal was influenced by biomass, elapsed time, temperature and daily irradiance, but not by either pH or depth. The concentration of ammonium nitrogen (NH4-N) was inversely correlated with temperature, biomass, depth, daily irradiance and daylength. Nitrification was found to occur with nitrate concentration showing a strong negative correlation with daylength, reflecting an increase in nitrifying activity by the pond biomass throughout the season. Nitrate concentrations were positively correlated with elapsed time, but negatively correlated with biomass, temperature and daily irradiance. Phosphorus removal was influenced by elapsed time and biomass concentration. Removal of biological and chemical oxygen demand (COD) at the completion of the batch runs was 96% and 78·6% respectively.

A microalga was isolated from the pack-ice of Wood Bay (Antarctica) during austral summer 1993–4. By comparison with an authentic strain obtained from Sammlung von Algenkulturen at the University of Göttingen (SAG 860–3), its ultrastructural details and pigment composition were very similar to those of Pleurochloris meiringensis. However, sequence analysis of the entire 18S rRNA gene revealed substantial genetic divergence (57 nucleotide substitutions and 19 insertions/deletions) between SAG 860–3 and the Antarctic isolate. Phylogenetic analysis of complete 18S rRNA gene sequences from 18 microalgal species, including the two strains studied, rejected the hypothesis that the Antarctic isolate is the sister species to Pleurochloris meiringensis. Molecular evidence indicates that the Antarctic isolate is the sister group of a clade that comprises two other representatives of the Xanthophyceae (synonym Tribophyceae): Pleurochloris meiringensis and Botrydiopsis intercedens. This leads us to conclude that this microalga is a new species belonging to a new genus and the name Pseudopleurochloris antarctica is proposed.

A new species of the widespread genus Mesophyllum Lemoine is described. Mesophyllum macedonis nov. sp. grows in shallow (c. 0·5 m depth) waters, tolerating wide temperature fluctuations (12–26 °C) at a salinity of 32–35‰, protected from direct wave and light exposure. The species forms weakly attached rose-coloured clumps with whitish margins on rocky substrata. Its thallus is composed of superimposed foliose lamellae (to 170 μm thick) with dorsiventral organization, non-coaxial hypothallium, limited perithallial growth (to 60 μm thick), rectangular epithallial cells and solitary terminal trichocytes. Tetrasporangial conceptacles are raised and have convex roofs perforated by up to 108 pores that are bordered by filaments composed of slender and occasionally elongated cells. Tetrasporophytes were first observed in 1984 and their occurrence monitored without finding gametophytes or other populations at the type locality or elsewhere on the coast of the Sithonia Peninsula. A comparative study of literature data and material of selected congeners shows that M. macedonis shares most of its characters with M. ornatum (Foslie et Howe) nov. comb. from the Bahamas and Mariana Islands, and M. incisum (Foslie) Adey from southern Australia and New Zealand. Biogeographic scenarios that may explain the restricted distribution of the new Mediterranean endemic are discussed.

Cryopreserved Chlamydomonas reinhardtii cultures remained viable when frozen by cooling slowly to −55°C, then plunging into liquid nitrogen for at least 1 day of storage. High viability (>40%) was retained when cultures contained 2–10% (v/v) methanol as a cryoprotective agent prior to freezing, while dimethyl sulphoxide was ineffective. However, methanol was lethal to cells in the presence of light. Frozen cultures became non-viable within 24 h when stored at −80°C, whereas those stored below −130°C remained viable for at least several months. Highest viability was attained in cultures that were frozen and stored at a low cell density. High viability also required that frozen cultures be warmed rapidly and the cryoprotective agent removed immediately thereafter in preparation for culturing in liquid or on solid medium. Individual cell viability was determined by measurements of colony counts after cell plating and by the penetration of Evans blue dye into non-viable cells. Viability in bulk culture was conveniently measured by comparing the rates of photosynthetic oxygen evolution, corrected for dark respiration, in previously frozen cultures with the corresponding rates in unfrozen controls. Cultures that had lost viability as measured by a decline in whole-cell photosynthetic oxygen evolution after freezing and thawing retained functional Photosystem II activity for some time thereafter, indicating that the loss in photosynthetic activity was due to some process other than photoinhibition of Photosystem II.

Tropical marine ecosystems are characterized by a specific cyanobacterial flora, temperature most probably being the major factor limiting the geographic distribution of the species. When compared with the open ocean, the highest biodiversity of cyanobacteria is observed in the littoral zones where they form intertidal and infralittoral mats, live as endoliths in carbonate substrates or form symbiotic associations, especially with sponges and ascidians. Their diversity, which especially in the less accessible infralittoral is still largely unknown, is also a source of diverse bioactive compounds, some of which are important as herbivore deterrents. As photosynthetic organisms, cyanobacteria sensu lato (including Prochlorophyta) are important contributors to benthic and open ocean primary production, but their main role in the tropical marine ecosystems appears to be as nitrogen fixers. Of primary importance in the often oligotrophic tropical oceans is the non-heterocystous, planktonic bloom-forming Trichodesmium, which probably represents a major nitrogen source for the marine and global nitrogen cycle.

The seasonal colonization and vertical zonation of adpressed and upright algae on Phragmites stems in Lake Belau, Germany, was investigated from November 1988 to October 1991. During the autumns and winters from 1988 to 1990 the dominant adpressed species included the diatoms Epithemia adnata, E. sorex, E. turgida and Rhopalodia gibba, while during the same seasons in 1990 and 1991, Cocconeis placentula var. euglypta was abundant. The upright diatoms were most abundant on the middle sections of the stems, whereas those epiphytes with most of their cell surfaces directly in contact with the substratum constituted the greatest part of the biomass on the lowest sections of the stems. Epithemia spp. and R. gibba attained their highest abundances near the sediment as well as buried beneath the most dense periphyton aggregations, while there were dense populations of C. placentula var. euglypta on the entire surface of the stems. Cocconeis is able to tolerate higher light intensities, with photosynthetically active radiation (PAR) values averaging 38 μmol m−2 s−1, than Epithemia and Rhopalodia, which settle at a significantly lower PAR (26 and 20 μmol m−2 s−1, respectively). The change in dominance among the adpressed species from Epithemia and Rhopalodia to Cocconeis can be explained by changes in the grazing habits of the snail Acroloxus lacustris.

Photosynthetic acclimation and the interactions between carbon (C) and nitrogen (N) metabolism have been studied in the red macroalga Gracilaria sp. from Cádiz, Spain, cultured under different inorganic C and N levels. The use of chemostats and buffered medium allowed continuous restoration of the alkaline reserve and constancy of pH during the experiments. The N∶C ratios and phycobiliprotein, chlorophyll a and soluble protein contents decreased when Gracilaria sp. was grown at low N levels. Algae grown in a high inorganic C concentration (5% CO2) displayed a higher soluble carbohydrate concentration and maximum photosynthesis rates but a lower photosynthesic affinity for inorganic C, and lower phycobiliprotein and Rubisco contents, than those cultured at low inorganic C levels (air CO2). The inorganic C enrichment also affected the N uptake and assimilation in Gracilaria sp., causing a decrease in the N uptake rate even under conditions of N sufficiency. These results reflect the significant influence of the inorganic C growth regime on N assimilation in Gracilaria sp.

Relationships between phytoplankton growth and supplies of phosphorus and nitrogen have been variously investigated in three lakes in two contrasted English lake areas using physiological nutrient indices (alkaline phosphatase activity, phosphorus debt, surplus phosphorus, phosphorus uptake kinetics, dark ammonium uptake, ammonium uptake kinetics, stimulation of 14C uptake, and batch bioassay) and by inspection of water chemistry. None of the lakes was significantly affected by wastewater effluent but all lay in agricultural catchments. Physiological indices and water chemistry suggested limitation of phytoplankton biomass mostly by phosphorus, and to some extent by nitrogen in summer in North Ormesby Broad, by nitrogen in summer and to some extent by phosphorus in Lily Broad and by nitrogen in White Mere. Indices did not always accord with one another, though were not severely misleading. They added little to conclusions that could be drawn from water chemistry alone. Reasons for the differential relative importance of nitrogen and phosphorus in the two lake areas are discussed. The paradigm of phosphorus limitation, though unchallenged in upland waters and those on poorly weathered rocks, may be less relevant in lowland lakes.

For activity and survival in extreme terrestrial Antarctic habitats, lithobiontic cyanobacteria depend on key biomolecules for protection against environmental stress and for optimization of growth conditions. Their ability to synthesize such molecules is central to their pioneering characteristics and major role as primary producers in Antarctic desert habitats. Pigmentation is especially important in protecting them against enhanced UVB damage during stratospheric ozone depletion (the Ozone Hole) during the Antarctic spring and subsequent photoinhibition in the intense insolation of the summer. To be effective, especially for the screening of highly shade-adapted photosystems of cyanobacteria, protective pigments need to be located strategically. Antarctic lithic cyanobacterial communities are therefore stratified, as in soil biofilms of Alexander Island, the benthic stromatolitic mats of ice-covered hypersaline lakes in the McMurdo Dry Valleys, and the endolithic communities within translucent Beacon sandstone outcrops of Victoria Land. The protective pigments include scytonemin, carotenoids, anthroquinones and mycosporine-like amino acids. To detect and locate photoprotective pigments in situ in free-living cyanobacteria and cyanolichens from hot and cold desert habitats, we have used Fourier-transform Raman micro-spectroscopy. With appropriate power inputs for labile molecules, this high-precision, non-intrusive laser-based technique can not only identify biomolecules in their natural state but also locate them spatially within the habitat relative to the components of the community, which require protection. In conjunction with direct and epifluorescence microscopy it provides a spatial and functional description of the protective strategy of a community. We present the unique Raman spectrum of scytonemin and use its primary and corroborative peaks to identify it within the plethora of other biochemical constituents of several natural cyanobacterial communities, including an Antarctic endolith. The remote-sensing aspect of this technique makes it suitable not only for spatial biochemical analysis of present and palaeontological Antarctic communities but also for analogous putative habitats on Mars.

Partial sequences of the large subunit (LSU) and small subunit (SSU) of the ribosomal DNA of fucalean algae (Phaeophyceae) from the northern and the southern hemispheres, as well as from other brown algal genera such as Durvillaea, were analysed and compared with available morphological data. Combined SSU+LSU sequence data appear to be suitable for inferring phylogenetic relationships within the Fucales. Results suggest that Durvillaea and Notheia should be included in the Fucales and that the paraphyletic Cystoseiraceae be merged into a large family, Sargassaceae Kützing emend. De Toni. The genus Axillariella, the taxonomic position of which was uncertain, clearly belongs to the Sargassaceae. At present, at least seven families are recognized in the order Fucales: Durvillaeaceae, Seirococcaceae, Notheiaceae, Sargassaceae, Himanthaliaceae, Hormosiraceae and Fucaceae. More investigations are needed to assess whether Xiphophora should be placed in its own family.

The production and composition of extracellular polymeric substances (EPS) in axenic batch cultures of the benthic marine epipelic diatoms Navicula salinarum and Cylindrotheca closterium were investigated. EPS was secreted into the medium and the bulk was loosely associated with the cells. Neither N. salinarum nor C. closterium formed a well-defined polysaccharide capsule. EPS of both N. salinarum and C. closterium consisted predominantly of polysaccharide but small quantities of protein were present as well. EPS also contained uronic acids and SO42− groups. Analysis of monosaccharides using gas chromatography showed that for both species glucose and xylose were the main constituents, but several other monosaccharides were present in smaller quantities. Two fractions of EPS were distinguished: a small amount was secreted into the medium and a second fraction was extracted in water at 30°C. For both species the two fractions differed somewhat in composition, indicating that they represented two different types of EPS. The EPS produced by N. salinarum and by C. closterium differed in their composition. The rate of EPS production in batch culture was highest during the transition from exponential growth to stationary growth. Negatively charged groups such as uronic acids and sulphated sugars determine the adhesion capacity of EPS and probably play an important role in the stabilization of intertidal sediments on which these diatoms grow and produce biofilms.

Geomicrobiological analysis of calcifying biofilms of three alkaline salt lakes characterized by moderate to high carbonate alkalinity indicates that microbial carbonate rock formation is not directly linked to cyanobacterial carbon fixation. The present review summarizes results from two published case studies that have been carried out at Pyramid Lake, USA, and Lake Nuoertu, PR China. New observations and data are presented for a current project on Satonda Crater Lake, Indonesia, that revise previous conclusions concerning the relationship between cyanobacteria and biofilm calcification. Extracellular polymeric substances (EPS) in the investigated lakes are mostly produced by cyanobacteria; their properties are discussed as key factors in biofilm calcification. In particular, EPS are capable of binding divalent cations (e.g. Ca2+) from the liquid phase by their carboxylate and sulphate groups. Therefore, despite a high supersaturation of the lake water with respect to calcium carbonate minerals, precipitation does not take place immediately. A delayed onset of precipitation can be achieved by a continuous Ca2+ supply that exceeds the Ca2+-binding capacity of the EPS, and/or an exoenzymatic degradation (decarboxylation, cleavage) of mucous substances that reduces the binding capacity and causes secondary Ca2+ release. The resulting microcrystalline precipitates are randomly distributed within the EPS, usually away from any of the living cyanobacteria. This suggests that the effect of photosynthetic CO2 fixation in increasing supersaturation is of secondary importance at high alkalinities. In contrast to biofilm-covered surfaces, calcium carbonate minerals nucleate and grow rapidly at surfaces poor in EPS when the critical supersaturation level for non-enzymatically controlled carbonate precipitation is reached. Examples of such surfaces poor in EPS are dead, lysed green algal cells and thin, discontinuous biofilms in voids of microbial reef rocks. Calcium carbonate crystals directly linked to cyanobacterial cells or filaments have been observed only exceptionally, e.g. on Calothrix.

Energy dispersive X-ray microanalysis (XRMA) in a scanning electron microscope (SEM) was used as a method to measure elemental silicon (Si) and phosphorus (P) in dinoflagellate cysts. Cysts were prepared by quick deep freezing and then freeze-drying, thereby avoiding the addition of preservatives. Cysts of Ceratium hirundinella collected from Lake Erken, Sweden and Esthwaite Water, UK, and Ceratium furcoides collected from Esthwaite Water, were analysed and compared. The hypothesis that cysts are able to assimilate P during dormancy was tested in the laboratory by incubating newly collected cysts of C. hirundinella in medium with and without phosphate. The analyses showed that there was no difference in P content between C. hirundinella and C. furcoides, suggesting that P content reflects differences in physiological status rather than species. C. hirundinella had a significantly higher Si content than C. furcoides, which agrees with earlier studies. Comparison of cysts of C. hirundinella from different years – 1995 (stored for 1 year), 1996 and 1997 – showed that the P content in cysts from 1995 was higher than that in cysts from the following 2 years, which indicates either that P was higher during encystment in 1995 or that cysts accumulated P during dormancy. The P uptake experiment showed a very slightly, but significantly, higher, P content in cysts incubated in P-rich medium.

A new species of Porphyra is described from the south western Cape, South Africa. The gametophyte of Porphyra aeodis sp. nov. grows epiphytically on Aeodes orbitosa (Suhr) Schmitz, and has a seasonal life history that matches that of its host. Although P. aeodis has been confused with P. capensis Kützing in the past, P. aeodis is more similar to the sympatric but epilithic P. saldanhae Stegenga, Bolton et Anderson. There is considerable morphological overlap between P. aeodis and P. saldanhae, although they may be distinguished using a combination of morphological and ecological characters. The taxonomic separation of P. aeodis and P. saldanhae was confirmed using isozyme electrophoresis.

The zygote wall in developing Durvillaea potatorum embryos is secreted soon after fertilization. Mucilage covers the surface of the zygote wall ensuring rapid adhesion of the newly fertilized egg. The zygote wall is replaced by new cell walls secreted by growing, dividing embryonic cells. Separation of the zygote wall from the embryo is evident 4 days after fertilization and is visible at the edge of the cap flanking the side of the developing embryo and/or at the curved part of the cap where it lifts away from the top of the embryo. At this stage the embryo has undergone an average of 8 cell divisions, increased 3 times in length, and started to increase in width. The zygote wall is eventually shed as it cannot accommodate embryo expansion. The growing embryo flicks out of the rigid zygote wall, which usually remains connected to the developing rhizoid by a mucilaginous strand. By day 5 the zygote wall has detached from the embryo in 22% of individuals and this increases to nearly 70% of individuals by day 10. Removal of alginate-gelling cations from the artificial sea medium indicates that the zygote wall has different properties from the underlying embryonic cell walls. Shedding of the zygote wall allows continued embryo growth, frees the embryonic thallus from the substratum and cleans the embryo surface of phenolic bodies and mucilage that are secreted soon after fertilization; it also removes micro-organisms colonizing the mucilage.

The unicellular, acido- and thermophilic red alga Galdieria sulphuraria is unique in its ability to grow heterotrophically on at least 27 different sugars and polyols. The enzymatic machinery necessary for metabolizing this variety of compounds is constitutively expressed in the alga. The uptake system, however, has to be induced. From in vivo studies we conclude that the uptake system consists of several transporters with a partly overlapping substrate specificity. These transporters can be grouped into hexose, polyol and pentose transporters. The mode of induction depends on the substrate supplied for heterotrophic growth. When autotrophic cells were supplied with hexoses, hexose and polyol transporters were induced from the onset of heterotrophic conditions. Depletion of substrate in the medium triggered the induction of other transporters. Dulcitol, as well as other polyols and pentoses, led to a co-induction of all transporters as judged from induction and competition experiments. The heterotrophic capabilities of Galdieria are intriguing, because the natural habitat of the alga contains only traces of organic carbon. The substrates for heterotrophic growth apparently originate from decaying cells releasing hydrolysed cell material. Trace amounts of glucose were sufficient for the induction of sugar uptake in Galdieria. The co-induction of transporters obviously enables the cells in endolithic mats to import a wide spectrum of organic carbon in order to survive periods of light limitation.