Examination of type material, comparative studies on vegetative characters and data from published accounts of sporangia, gametangia and spermatozoids are used here to further develop and strengthen generic and species concepts in Zonaria and Homoeostrichus. Zonaria is characterized by octosporangia which lack a stalk cell and occur among whitish paraphyses, by the presence of cortical cells in indusiate sporangial and oogonial sori, and by slightly elongate sterile cells bordering the antheridial sori. Other characters (mucilage in sporangial and oogonial sori, biflagellate sperm with a row of many tall spines along the anterior flagellum) may also be diagnostic of Zonaria but have not been demonstrated in the generitype. Eight species are retained in Zonaria. Generic placement of Zonaria stipitata, described on vegetative characters, requires confirmation. Homoeostrichus, as typified by Homoeostrichus sinclairii, is defined by the presence of brown paraphyses in nonindusiate sporangial and oogonial sori and bordering antheridial sori, a multicellular sporangial stalk, oogonia without a stalk cell, and uniflagellate spermatozoids. Zonaria harveyana and Homoeostrichus olsenii are similar in sporangial structure, but they cannot be assigned to either Zonaria or Homoeostrichus as now defined and consequently are transferred to the new genus, Exallosorus, as Exallosorus harveyanus (Pappe ex Kützing) comb. nov. and Exallosorus olsenii (Womersley) comb. nov. Exallosorus is distinguished from Zonaria and Homoeostrichus using sporangial characters: tetrasporangia have a stalk cell and are closely packed into indusiate sori which lack paraphyses and mucilage. Problems in obtaining reliable species identification for the five southern Australian species of Zonaria are partially resolved. This study demonstrates again the essential contribution of reproductive characters to the definition of taxa and supports the position that decisions to erect, subsume or transfer members of the Dictyotales should be based on more than vegetative characters.

As a basis for inferring phylogenetic relationships between Pelvetia and Pelvetiopsis in the family Fucaceae, the complete sequences of the plastid-encoded RuBisCo spacer region were determined for all four species of Pelvetia, for the type species of Pelvetiopsis, P. limitata, and for three other fucacean species (Ascophyllum nodosum, Fucus gardneri and F. vesiculosus). All trees based on the sequences of the RuBisCo spacer region showed that Pelvetia is not monophyletic and consists of two clades, one including P. babingtonii, P. compressa, and P. siliquosa, the other comprising only the type species, P. canaliculata. P. canaliculata is not closely related to any of the other Fucaceae studied, and it may represent a monotypic genus. RuBisCo spacer sequences support the establishment of a new genus for the three Pacific Pelvetia species: P. babingtonii, P. compressa and P. siliquosa. The congruence of the RuBisCo spacer data with reported nuclear rDNA 18S and ITS sequences, and with biogeographical and morphological data, indicates that the RuBisCo spacer region, including its flanking areas, is useful for inferring phylogenetic relationships within the Fucaceae.

Growth rates in terms of area expansion per 30 min were measured in the red alga Porphyra leucosticta under different light/dark (LD) cycles, irradiance levels and light qualities. Twelve hours per day under white light (35 μmol m−2 s−1) promoted a dramatic and rapid increase in thallus expansion during the first part of the light period followed by low values during the remaining light and dark phase. Light/dark regimes of 8[ratio ]8 h, 6[ratio ]6 h, 3[ratio ]3 h and 1·5[ratio ]1·5 h resulted in a discontinuous growth pattern where thallus expansion was restricted to the light phase while no growth occurred in the dark phase, and there was even a significant thallus contraction just after light-off. Growth rates in terms of percentage area increased with irradiance at LD 12[ratio ]12. This was due to: (1) the phase of high growth rate following the initial ‘morning peak’ extending from the first 6 h of the light phase to cover almost the entire light phase, and (2) an increase in growth rate during the second half of the night phase. Saturation was reached at an irradiance of 125 μmol m−2 s−1. An irradiance of 500 μmol m−2 s−1 decreased thallus expansion rate during the light and dark culture phases relative to the other irradiances used. Light quality also caused changes in growth rate: the maximum value was reached under yellow light followed by red; both of these were higher than the growth rate under white light. Blue light (35 μmol m−2 s−1) caused a decrease of more than 50% in thallus expansion compared with white or red light due to a very dramatic decrease in the ‘morning peak’ of thallus expansion and very low values in the rest of the light and dark phases. Increasing the percentage of blue light in different white light sources also decreased thallus expansion. It is suggested that light influences the growth of Porphyra in three ways: as an external signal matching thallus expansion with light and dark cycles; as an energy source promoting thallus expansion with increasing irradiance; and, at a morphogenetic level, inhibiting growth in blue light.

Batch culture experime nts were conducted with Alexandrium ostenfeldii, a toxic, marine dinoflagellate common in Danish waters. Growth occurred at 11·3–23·7 °C and from 10 to 40 psu.Maximum division rates of more than 0·3 di visions d−1took place at 20 °C and 15–20 psu. Growth phase variations resulted in mean cell sizes from 12 × 103 to 20 × 103 μm3. Variations in cell size were observed at differ ent temperatures and salinities, and mean cell size was closely correlated with division rate for all temperatures investigated (11·3–23·7 °C) and for salinities between 10 and 30 psu. Sexual stages, fusing gametes and planozygotes were observed in nutrient-deficient cultures of A. ostenfeldii from New Zealand, but mixing of two Danish nutrient-deficient, clonal cultures did not result in mating. Sexual fusion did not lead to the formation of resting c ysts, which are presently known only from nature. Temporary cysts were very common in ageing cultures and in unfavourable environmental conditions that did not permit growth. These cysts showed a high degree of morphological variability. When st ained with calcofluor, the cysts revealed a surface pattern. Germination of temporary cysts caused the release of a naked, biflagellate stage. At germination, the transverse flagellum was located outside the cingulum, next to the longitudinal fl agellum. The transverse flagellum became positioned in the cingulum only after the cell was clear of the cyst wall.

Carbon and nitrogen contents of two intertidal fucoid species, Fucus serratus and Himanthalia elongata, were investigated with respect to variations in seasonal resource availability, growth and reproductive requirements. The linear growth rate of F. serratus peaked in spring at 2·3 cm 28 d−1, compared with <0·1 cm 28 d−1 in the winter. In H. elongata, the button diameter increased slowly throughout the year (<0·22 cm 28 d−1) ; in contrast, the receptacle had an elongation rate of up to 7·8 cm 28 d−1 in the spring months. There was no difference in the nitrogen content (% dry weight, dwt) of the vegetative tissue of both non-reproductive and fertile thalli and receptacle tissue of F. serratus, but the nitrogen content of all three tissue types varied seasonally. Reproductive development was initiated in May when nitrogen content was at its peak (3 % dwt). Tissue nitrogen content decreased rapidly through reproductive development to a minimum of less than 1·5% dwt in August; this decrease also occurred in non-reproductive thalli. Tissue nitrogen varied between 0·5 and 1·75% dwt in the vegetative buttons on both non-reproductive and fertile H. elongata, but not in a distinct seasonal manner. Receptacle development in H. elongata was initiated in October/November. The nitrogen content of the receptacle tissue increased rapidly in the first two months of reproductive development (up to 2·5% dwt) then progressively decreased throughout the remaining period of reproductive development. There was no evidence of carbon storage in the vegetative tissues of either F. serratus or H. elongata.

This is the first description of a combination coccosphere of the heterococcolithophore species Coronosphaera mediterranea (Lohmann 1902) Gaarder in Gaarder & Heimdal (1977) and the holococcolithophore species Calyptrolithophora hasleana (Gaarder 1962) Heimdal in Heimdal & Gaarder (1980) (Figs 1, 2). A single specimen of this new combination coccosphere was found within 53000 analysed cells in one of 189 samples collected at the JGOFS time series station ALOHA, Hawaii, during 1993 to 1996. The specimen was in a sample collected during autumn 1996 at a water depth of 5 m at a temperature of 26·1 °C, salinity of 35·0 psu, phosphate of 0·002 μmol/kg and in nitrate-depleted water (for details see Cortés, 1998; Cortés et al., 2001).

The early life stages of Hormosira banksii can be viewed as a series of distinct developmental events such as gamete release, fertilization, germination, adhesion, cell division, apical hair formation and growth. These developmental stages can be targeted for experimentation as well as used as a measure of health in bioassay tests. Three bioassays were devised and compared to determine which developmental events in H. banksii are most susceptible to effluent (40%) and/or reduced salinity (21‰ S). These treatments approximate conditions in the shore zone where H. banksii once occurred at Boags Rocks, Victoria, Australia. Reduced salinity and sewage effluent affected developing H. banksii differently. Damage caused by reduced salinity occurred within the first 48 h and affected fertilization and germination. Exposure to sewage effluent did not affect fertilization but reduced the number of healthy embryos that had formed a wall by 24 h, germinated by 48 h and divided by 72 h. Both sewage effluent (40%) and reduced salinity (21‰ S) significantly decreased the number of healthy developing embryos that had adhered by 24 and 48 h.

The population of Stephanodiscus rotula in a temperate eutrophic lake was studied over a 2 month period (January to early March). Although during the study period nutrient concentrations in the lake water remained far in excess of phytoplankton requirements, no notable increase in chlorophyll levels was recorded. This suggests that algae were limited by shortage of light and low temperatures. Frequency distribution analysis of cell diameters showed a dramatic size reduction at the end of winter, followed by restoration of higher values by early spring. Electron probe X-ray microanalysis spectra from Stephanodiscus cells routinely showed peaks of Ca, K, Si, P, S, Fe, Al, Mn, Mg, Na and Cl, with substantial variation in elemental concentrations both between and within samples. End-of-winter reduction in the cell size coincided with a considerable depletion of intracellular chemical levels of Si, P, Cl and K and could be related to the concurrent decrease in dissolved organic C and increase in intracellular Al. Correlation and factor analysis of intracellular elemental concentrations showed that statistical elemental associations within Stephanodiscus cells were mainly determined by three factors, with P, Cl, Si and K showing higher loadings on the first, Ca, Mn and S on the second, and Fe, Ca and Al on the third factor. Significant correlations among the elements of the first association may indicate the importance of P (ATP), K (through involvement in P metabolism) and Cl (possibly charge balance) in the active Si uptake during the study period.

Molecular phylogenetic relationships among sexually isolated subpopulations (syngens) of the morphologically defined volvocacean flagellate Pandorina morum (O. F. Müller) Bory are inferred from sequences of the internal transcribed spacer regions (ITS-1 and ITS-2) of the nuclear ribosomal DNA repeats. The resolved phylogenetic lines are composed of strains with very similar sets of traditional characters, such as zygote aggregation pattern, chromosome number and cell division timing, and are correlated with the distribution pattern of the xanthophyll loroxanthin [(3R,3′R,6′R)-β,ε-carotene-3,19,3′-triol]. Thus, loroxanthin, a phylogenetic character within the Volvocales, is also of value at the infraspecific level in P. morum, a morphologically uniform species complex, within the Volvocales.

Chlamydomyxa labyrinthuloides is a heterokont alga known since the last century. It lives on Sphagnum and other water plants as aplanospores or plasmodia. We have investigated the taxonomic position of Chlamydomyxa labyrinthuloides by combining results from morphological studies, pigment analyses and a molecular phylogenetic analysis of the small subunit (SSU) rRNA gene. Chlamydomyxa labyrinthuloides shares morphological features with xanthophytes and chrysophytes, whereas pigment composition indicates a grouping with the phaeophytes, raphidophytes and chrysophytes. The sequence of the SSU rRNA gene and its phylogenetic reconstruction unambiguously demonstrate that Chlamydomyxa labyrinthuloides is related to the chrysophytes.

Quantification of the iron nutritional status of phytoplankton is of great interest not only for the study of the oceans but also for fresh waters. Flavodoxin is a small flavoprotein proposed as a molecular marker for iron stress, since it is induced as a consequence of iron deprivation, replacing the iron-sulphur protein ferredoxin. Flavodoxin and ferredoxin from Scenedesmus vacuolatus have been immunoquantified in cells grown under different iron nutritional conditions. Flavodoxin and ferredoxin levels correlate with the iron availability, and the calculated flavodoxin index can be used as an iron-stress marker. Other physiological parameters such as copper deficiency, heterotrophic or mixotrophic growth, nitrogen source and salt stress were also tested as potential factors influencing flavodoxin expression. Salt stress and heterotrophic growth conditions alter flavodoxin and ferredoxin expression. Once flavodoxin expression is repressed by iron (and severe deficiency alleviated), S.vacuolatus still increases its ferredoxin from 0.5 to 1.6 mol of ferredoxin per mole of ferredoxin-NADP+ reductase, and this ratio can be used for the evaluation of mild deficiency.

A new diatom (Bacillariophyceae) genus and two new species are described from the arid region of the North American southwest. The new genus, Playaensis, and new species, P. circumfimbria and P. furtiva, are distinguished by frustule morphology and autecology. Playaensis possesses unique, narrowly lunate longitudinal ribs bordering the raphe and spathulate spines, but their evolutionary relationship to known genera is unclear. In Payton Lake, New Mexico, P. circumfimbria and P. furtiva are rare in the diatom community, and their geographic and geological extent are not known, but they may be restricted to alkaline, slightly saline lakes of the region.

The marine red alga Laurencia japonensis sp. nov. (Rhodomelaceae, Ceramiales) is described from the warm temperate region of Japan. It is characterized by the following combination of features: (1) terete, rigidly cartilaginous, upright axes arising from a primary discoid holdfast and stolon-like branches; (2) tristichous branching; (3) penultimate and ultimate branches showing pronounced adaxial bending; (4) adventitious branches formed chiefly in the axils; (5) the production of four periaxial cells per vegetative axial segment; (6) the presence of longitudinally oriented secondary pit connections between contiguous superficial cortical cells; (7) the absence of projecting superficial cortical cells; (8) the absence of a radially elongated cortical layer; (9) the presence of abundant lenticular thickenings in the walls of medullary cells; (10) the presence of a single corps en cerise per superficial cortical cell and trichoblast cell; (11) a parallel arrangement of tetrasporangia; (12) broadly ovoid cystocarps with the lower half immersed within the parent branch tissue; and (13) distally positioned spermatangial nuclei.

The stress-70 protein family has previously been shown to be a useful tool for molecular phylogeny at the kingdom to family levels. Although sequences of many members of the stress-70 family are available, few genes from the Protoctista have been sequenced to date. Phylogenetic analyses of algae based on various molecules have not, as yet, provided clear results concerning relationships between major divisions. We cloned and sequenced several algal stress-70 genes in order to provide additional data and to further analyse phylogenetic relationships among algal divisions. New nuclear sequences were obtained from Guillardia theta (Cryptophyta), Ascophyllum nodosum (Heterokontophyta) and Cyanophora paradoxa (Glaucocystophyta). Phylogenetic trees of the stress-70 protein family calculated using different methods are presented. In our trees, the heterokont alga Ascophyllum nodosum is closely related to the slime mould Dictyostelium discoideum, while the nucleomorph (eukaryotic endosymbiont) of the cryptophyte Rhodomonas salina seems to be related to the chlorobiont lineage. The glaucocystophyte Cyanophora paradoxa and the nuclear sequence (host) of the cryptomonad alga Guillardia theta also seem to be closely related. The Cryptophyta and the heterokont algae have evolved from different secondary endosymbiotic events involving different hosts and probably different endosymbionts. However, until more stress-70 sequences of algal divisions become available no definitive conclusions can be drawn concerning branching of the major divisions.

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.

In summer, the concentrations of dissolved organic nitrogen compounds are often higher than that of inorganic nitrogen. Under such conditions it would be advantageous if phytoplankton species could utilize organic nitrogen sources, including free or combined amino acids, in addition to inorganic nitrogen. This study focused on histidine, the degradation of which potentially yields three nitrogen atoms for each molecule of histidine. In this work, histidase from Dunaliella tertiolecta, a deaminating enzyme catalysing the first steps of histidine degradation, was purified 4000-fold and partially characterized. The molecular weight of the native enzyme was estimated to be 155 kDa, corresponding to four subunits of 38 kDa. D. tertiolecta histidase is stable in the presence of dithiothreitol and is inactivated by cyanide. Histidinol phosphate, histidine and Mn2+ are effective protectors against cyanide inactivation. The enzyme did not exhibit classical Michaelis-Menten kinetics but showed a relationship between the rate of catalysis (V) and the concentration of substrate (S) that was characteristic of negative allosteric behaviour. A Hill coefficient of 4 was measured for histidine concentrations higher than 22.5 mM. Guanine, xanthine and cytosine nucleotides are inhibitors of D. tertiolecta histidase.

The marine brown alga Myriotrichia clavaeformis (Dictyosiphonales) is the host of a large icosahedral virus with a double-stranded DNA genome, MclaV-1. This pathogen replicates exclusively in prospective reproductive organs of the alga. We studied the assembly of virus particles by transmission electron microscopy. Replication of viral DNA starts in the nucleus, which hypertrophies and later disintegrates. Capsid assembly begins in the cytoplasm by budding from virus-detaching bodies. After nuclear breakdown, assembly continues in a mixed cyto-/nucleoplasm on membrane cisternae, which probably originate from the endoplasmic reticulum. Virus particles thereby acquire as an integral capsid component a membrane to which proteins are apposed. Material inside the capsids partly condenses to form an additional layer in the core shell. DNA is packaged after capsid formation, giving rise to an electron-opaque nucleoprotein core. M. clavaeformis infected by MclaV-1 is the second brown algal host-virus system in which virus assembly has been studied in detail. Together with previous observations, our results allow conclusions on general mechanisms of virus assembly in brown algae. Some features of virus formation in brown algae show similarities with large icosahedral DNA viruses infecting animal cells.

The fine structure of the flagellar apparatus of male gametes of Ectocarpus siliculosus has been studied in negatively stained whole-mount preparations of isolated flagellar apparatuses and by transmission electron microscopy of embedded whole cells and flagellar apparatuses. Reconstructions from serial sections revealed a single absolute configuration and new structural details of the flagellar apparatus. A set of 5 microtubular roots is associated with the 2 flagellar basal bodies: the major anterior root consisting of 9 microtubules originates at the anterior basal body and loops through the anterior part of the cell. Cytoplasmic microtubules originate from this root at the apex of the cell and splay out in a posterior direction through the cell, thus determining cell shape. A broad microtubular band composed of a 9-membered bypassing root and a 3-membered major posterior root runs across the basal bodies. Two additional flagellar roots, the minor anterior and minor posterior rootlets, consist of a single microtubule each. The proximal end of the posterior basal body is laterally connected to the anterior basal body by a cross-striated connective (deltoid band). The basal bodies are connected to the nucleus by a small rhizoplast, and several other fibrous structures are associated with the basal bodies. The results are discussed in relation to earlier observations on flagellar apparatus organization in brown algae.

Blue light stimulates photosynthesis in brown algae by activating a mechanism for carbon acquisition. As this is connected with liberation of CO2 from an internal pool, it had previously been suggested that a C4 pathway might operate, with CO2 mobilization from an intermediate mediated by the action of blue light. The possibility that such a C4 mechanism functions was tested in Ectocarpus siliculosus by investigating metabolite pools and carbon fixation products. Extracts were analysed by HPLC with an ion exchange column. With the exception of citrate/isocitrate all metabolite levels were far too low to serve as the intermediate pool. No changes in the concentrations of any of the metabolites were found after activation by blue light following red light pre-irradiation. During short-term incubations with 14C inorganic carbon, the major label was found in phosphoglycerate. There was also clear labelling of peaks containing malate plus pyruvate and in citrate/isocitrate. In addition, glycerate contained high levels of radioactivity in some culture strains of Ectocarpus siliculosus. In chase experiments, the radioactivity of all metabolites continued to increase, indicating the presence of considerable amounts of intracellular inorganic carbon. Transient labelling was not observed for any of the fixation products. When Ectocarpus was pre-irradiated with red light and then stimulated by blue light, fixation rates increased with a time course that correlated with the activation of oxygen evolution. Photosynthetic oxygen evolution was investigated in vivo after the addition of possible intermediates to carbon-free seawater. Most of the exogenous applied substrates did not enhance photosynthesis, either in red light or after blue light stimulation. A strong enhancement seen after the addition of oxaloacetate was most likely due to release of CO2 during the breakdown of the metabolite in the medium. Taken together, the data argue strongly against the operation of a C4 pathway in Ectocarpus. It is suggested that the internal pool mobilized by blue light contains inorganic carbon.