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.

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.

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.

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.

We report the cloning and characterization of a 1881 bp Thalassiosira weissflogii (Bacillariophyceae, Centrales) plastid genomic fragment containing the ferredoxin gene (petF) and several other genes. The organization of this fragment is exactly the same as its equivalent region from the plastid genome of another centric diatom, Odontella sinensis, and the sequences share high homology in both coding and non-coding regions. Traces of a probable vestigial protein-coding gene and of a partial trn gene are found just after the trnR gene in both diatoms as well as in the plastid genome of the red alga Porphyra purpurea, illustrating the close relationship between red algal and heterokont algal plastid genomes and arguing in favour of the origin of the latter by secondary endosymbiosis. In accordance with phylogenetic analyses of most plastid genes, phylogenetic trees inferred from 69 ferredoxin sequences show that both the green and the red algal plastid genes arose from cyanobacterial genes; our results furthermore suggest that each of these plastid lineages is related to different extant cyanobacterial genes, implying either that different endosymbiotic events were responsible for the origin of green and red plastids or that each lineage kept only one (and a different one) of several paralogous cyanobacterial genes present in the ancestral cyanobacterial genome.

Fine structure of vegetative cells, development and morphology of sporangia and general morphology of zoospores were studied for the first time in the genus Endophyton Gardner. Vegetative cells contained one parietal perforate chloroplast with 2–4 ulvophycean pyrenoids and transverse cell walls without plasmodesmata. Sporangial walls were formed by two distinct electron-dense and fuzzy layers which contained a contiguous electron-translucent, fibrillar material. Zoospores were naked, with an anterior dense aggregation of vesicles and a cup-shaped chloroplast with one eyespot. The flagellar apparatus showed 180° rotational symmetry and counterclockwise absolute orientation of its components. Microtubular roots had a cruciate pattern, in which d=2 and s=4 with 3/1 arrangement. Electron-dense bilobed terminal caps covered the proximal end of each basal body. These observations support the suggested close relationship of Endophyton to the allied genus Entocladia and other ulvalean algae, and reinforce the criteria for including the genus in the class Ulvophyceae, order Ulvales, family Ulvellaceae.

Biological classification has been successively shaped by Neoplatonism, ideas of plenitude and one-dimensional continuity (the Great Chain of Being), two-dimensional continuity (Linnaeus's map), idealized comparative morphology and development and, through phylogenetic theory, Darwinian descent with modification. Concepts of Algae have thus evolved within a succession of very different paradigms. Algae have been imperfect plants; a segment of the Great Chain; the least-developed members of vegetative form-series; and primitive forms from which plants (and even animals) can be elaborated. The idea of a single grouping of simple organisms, formalized by Bory de Saint-Vincent and others in the early nineteenth century, was developed in a phylogenetic framework by Haeckel as Protista. Most macrophytic algae, however, remained Plants until Copeland merged eukaryotic non-green algae into Protista. Arrangements of algal taxa within form-series, and recognition of Algae and Protista as taxa, are incompatible with Hennigian phylogenetic systematics (cladistics). Developing genomic perspectives threaten to undermine established concepts of organismal lineage and higher-level biological classification.

Effects of irradiance and temperature on the Mediterranean red algae Eupogodon spinellus and Eupogodon planus were tested. Growth of both species was saturated at an irradiance of 10–20 μmol m−2 s−1, which is in accordance with their sublittoral habitat. Eupogodon spinellus and E. planus survived permanently at temperatures between 8 and 30 °C. The temperature optimum for growth was 25 °C with suboptimal growth occurring at (10−)15 and 30 °C in both species. At their collection locality (Corsica), potential monthly growth yields would be highest in summer and in winter would be only about 20% of the maximum. Reproductive requirements could be determined only in E. planus. Gametophytes reproduced both in long and in short days but only at 20 °C. Tetrasporophytes reproduced at 15–20 °C but only in short days. Geographic distribution boundaries are not set by growth or survival limits. However, the reproductive requirements of E. planus did account for its restricted distribution in the Mediterranean and on the Canary Islands.

Three marine planktonic species of the diatom genus Chaetoceros were studied by light and electron microscopy, from net samples collected from different tropical and subtropical areas: coasts of Baja California, the Gulf of Tehuantepec (both in the Pacific Ocean), the Gulf of Mexico (the Atlantic Ocean) and the Indian Ocean. Two of the species, Chaetoceros pseudodichaeta and C. pseudoaurivilli, were originally described by Ikari in 1926 from Japanese waters. This is the second record of them. C. pseudodichaeta is superficially similar to C. dichaeta but detailed morphology differs, especially that of the intercalary setae, which are four-sided in cross-section, with long spines at the edges, and a pattern of two striae between two costae. Chaetoceros pseudoaurivilli is a distinctive species with a characteristic dome- shaped protuberance on terminal valves and the presence of various rimoportulae on, at least, terminal valves of the chain. Finally, C. pseudosymmetricus is a species only reported twice in the Indian Ocean. Its distinctive character is the heteropolarity of terminal setae: one is coarse, long and strongly curved, and the other is delicate, shorter and smoothly curved. It also has a single rimoportula on terminal valves only. The three species are regarded as rare, and consequently our knowledge of their distribution is rather poor. Additional taxonomic comments are provided for the three species.

A comparative study of fertile gametophytes has been carried out on six species of the Dictyotales from Australia. Patterns of gametangial distribution and structure are similar in Zonaria angustata, Zonaria diesingiana, Zonaria spiralis and Zonaria turneriana, but there are some marked differences apparent between both Homoeostrichus olsenii and Homoeostrichus sinclairii and the Zonaria species. Sterile cortical cells and mucilage between the cylindrical oogonia are characteristic of the indusiate female sori of Zonaria, which differ markedly from the comparable structures of H. olsenii, in which all cortical cells have been transformed into oogonia and the walls of adjacent oogonia are contiguous. In contrast, the large spherical oogonia of H. sinclairii are unique in the Dictyotales, lacking a stalk cell and occurring among brown paraphyses in a large non-indusiate sorus on each terminal branch segment. Antheridial sori of the six species exhibit far less structural variation than the oogonial sori. Male sori are surrounded by undifferentiated cortical cells in H. olsenii, by tall brown paraphyses and short paraphyses in H. sinclairii and by sterile cells in Zonaria spp. Short paraphyses form only around the male sori of H. sinclairii in the Dictyotales; they differ in structure from the brown paraphyses but are similar to the antheridia, from which they may have been derived. Gametangial characters have proved invaluable in defining the genus Zonaria and in separating H. olsenii from H. sinclairii, but they cannot be used to delimit the species of Zonaria. Furthermore, the differences observed in the gametangia have provided new characters for phylogenetic analyses, as well as providing further supporting evidence for the recognition of Zonaria and Homoeostrichus as distinct entities.

Light microscopy and scanning electron microscopy were used to study Amphidinium glabrum sp. nov., a new dinoflagellate species from tidal sand flats in the North German Wadden Sea and from the surface water and the lowermost layer of first-year ice in the European Arctic. Cells are strongly flattened dorso-ventrally, with nearly parallel sides in ventral view. The distal region of the strongly displaced cingulum is not connected with the sulcus. There is no surface striation. The sulcus extends from the antapex, where it forms a large excavation, to the apex and further onto the dorsal side of the epicone. The new species is compared with two morphologically similar dinoflagellates: A. scissum Kofoid & Swezy and A. scissoides Lebour. Characters that distinguish the three taxa are: cell shape and size, shape of epicone and hypocone, cell surface, cingulum displacement, distal region of the cingulum and antapical notch.

DNA of Chara vulgaris thalli contains target sequences for the methylation-sensitive restriction enzymes, Sau3A, HpaII and MspI. These enzymes were used with the in situ nick-translation radioactive technique to evaluate by grain counting in autoradiograms changes in cytosine methylation during antheridial filament development and spermiogenesis. In successive generations of dividing antheridial filaments the level of DNA methylation gradually increases, then decreases slightly in the early stages of spermiogenesis. Spermatozoids display the highest level of DNA methylation.

A new diatom genus and species, Australodiscus peruvianus Porguen et Sullivan, is described from an Eocene marine deposit from the Paracas Peninsula, Peru. The valve outline is stellate with ocelli and rimoportulae situated singly on alternate points of the star. The rimoportulae are winged and situated on a secondary marginal ridge. Three types of spines are present; two of these are also winged. Our new form appears to be best placed for the present in the centric family Triceratiaceae (Schütt) Lemmermann, being most closely related to the type genus Triceratium Ehrenberg and Grovea A. Schmidt.

Crosses were performed to identify the sources of variation in zygote production (via cystocarp production) in Gracilaria gracilis, a red haploid-diploid seaweed. First, because male gametes are short-lived (<6 h), the rate of gamete encounters was evaluated in a time-course experiment. Second, the effect of water motion on gamete encounters was assessed by introducing turbulent eddies in the crossing tank and by comparing fertilization rates with and without this added turbulence. Third, variation due to individual performance was explored by performing multiple-donor crosses using 12 males and 12 females from three populations. Paternity of cystocarps produced in these crosses was determined using microsatellite markers. The results show that cystocarp yield increased with exposure time: fertilization occurred in as little as 15 min after the introduction of male branches into the crossing tank and maximum cystocarp production values were observed at 6 h. There were no significant differences in cystocarp production between the two turbulence levels. On the other hand, cystocarp production was highly influenced by male and female parental identities and to a lesser degree by an interaction between the male and female parents. The variation in cystocarp production according to male and female identity was not due to population origin as there was no difference between intra- and inter-population crosses. Thus non-random mating occurs in controlled conditions and arises from differential performance in G. gracilis. There was a strong deviation from equality of male performance, implicating post-adhesion events and/or male gamete production as important in generating non-random mating. Consequently, non-random mating may play a role in the evolution of mating patterns in G. gracilis.

The apex of the tetrasporangial branches of Osmundea spectabilis var. spectabilis (= Laurencia spectabilis var. spectabilis) exhibits cavities in which tufts of multicellular trichoblasts occur. Trichoblast development in Osmundea spectabilis var. spectabilis begins with the differentiation of an epidermal cell within the crypt. This cell differentiates into a trichoblast mother cell (TMC). The TMC divides to form a two-celled incipient trichoblast. Successive periclinal divisions of the apical cell of the young trichoblast result in the formation of a multicellular developing trichoblast. With the exception of the apical cell all trichoblast cells are at the same developmental stage. They possess a large nucleus, abundant plastids with peripheral and some internal thylakoids and dictyosomes. Daughter chloroplasts result from one constriction or multiple fission of a single chloroplast. Dictyosomal cisternae and mucilage sacs contribute material to wall formation. Each differentiating trichoblast cell is surrounded by a bi-layered wall. The outer wall layer represents the trichoblast mother cell wall and the inner wall layer is the trichoblast cell wall. Mature trichoblast cells have thin walls, probably as a consequence of mucilage extrusion, the most likely function of trichoblasts in Osmundea.

Ultrastructural observations on the vegetative filaments, motile cells and processes leading to zoospore differentiation in Chrysonephos lewisii are presented. Vegetative filaments are embedded in a mucilaginous envelope, preserved by Alcian blue fixation, which favours their aggregation and also the attachment of bacteria, diatoms and various types of debris. The filaments are provided with an external wall consisting of microfibrils positive to the PATAg test and ConA-colloidal gold labelling. Inside the filaments the vegetative cells differentiate into zoospores. This accounts for the ultrastructural similarity between vegetative cells and zoospores, although zoospores are typically provided with a flagellar apparatus. They share an external cell covering or theca, vacuolar or cytoplasmic ‘scale-like structures’, protruding stalked pyrenoids, scattered nucleoids of plastid DNA and absence of a photoreceptor-eyespot complex. The flagellar apparatus of zoospores is characterized by two distinct basal plates, the central pair of flagellar microtubules originating some distance above the transitional plate and basal body angle less than 90°. These results provide strong taxonomic evidence that this genus should be placed in the Sarcinochrysidales sensu stricto, rather than remaining in Chrysomeridales. The key role of the Golgi apparatus in the synthesis of different structural elements – depending upon the functional stages of the cells – and in the processes of exocytosis during zoosporogenesis is also discussed.

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.

The stimulating effect of blue light on the carbon-concentrating mechanism of Ectocarpus siliculosus was investigated by measuring the intracellular pools of inorganic carbon (Ci) in red light (low photosynthetic rates) and in red light plus blue light (high photosynthetic rates). Ci accumulated in red light to about twice the levels found in the presence of blue light, but the permeability of the cell membranes for Ci, measured as the rate of influx of tracer carbon, was similar in both light conditions. This was also true after the seawater pH was adjusted to pH 9·5, when bicarbonate should be the only inorganic carbon species to enter the cells. Activation of photosynthesis after prolonged red light caused the accumulated Ci to decline to levels similar to those observed in blue light. The time course of this decline was rapid and coincided with the time course that was expected for the emptying of a carbon pool whose existence had been demonstrated earlier in measurements of photosynthetic oxygen evolution in the absence of external carbon. The accumulation of Ci in red light required active photosynthesis, but it also occurred in the presence of inhibitors of carbonic anhydrase activity. It is suggested that blue light mobilizes the Ci pool by causing changes in intracellular pH and that the size of the pool depends on the activity of metabolic CO2-sink activities that are also under the control of blue light.

Comparison of karyology, restriction patterns and DNA methylation levels (as gender separation could be related to some epigenetic mechanism, e.g. DNA methylation) has been performed between male and female individuals of the dioecious species, Chara tomentosa. In contrast to angiosperms, sex determination systems in Charophyceae have not been studied. High-performance liquid chromatography (HPLC) showed that the cytosine methylation level in female plants of Chara tomentosa reached 5·9 %, while in male plants it reached 9·1 %. Karyological analysis did not show any differences in metaphase chromosome number or morphology between sexes. Cytophotometric measurements of DNA content revealed differences in 1C DNA content: 7·0 pg in females and 7·4 pg in males (p < 0·001). Computer image analysis showed that in the interphase nuclei condensed chromatin consists of 34·3 % of the total chromatin in female plants, while in males it was 29·6 % of total chromatin (p < 0·001). Digestion of isolated DNAs with 12 enzymes showed poor enzymatic cleavage (for example with SacI) or restriction patterns which differed between the sexes (TaqI, Bst0I). The restriction endonucleases RsaI and BamHI revealed repetitive DNA families in males. BamHI generated bands of over 3000 bp while RsaI revealed populations of fragments 650–2000 bp long. DNA isolated from male individuals of C. tomentosa was less susceptible than DNA isolated from female plants to digestion with enzymes that are inhibited by methylation of dC residues (HpaII, HhaI).

Bitectatodinium tepikiense Wilson cysts, first described from Pleistocene sediments and generally associated with sediments in temperate to cold-temperate waters, were germinated to establish cultures. The motile thecate cells derived were referable to Gonyaulax digitale (Pouchet) Kofoid. For the first time detailed morphological information is given for the motile stage of this cyst–theca relationship. Cultures were re-encysted; the cultured cysts showed a range of morphology from spherical cysts to those with an apical boss. The taxonomy of Gonyaulax digitale and cyst–theca relationships within the Spiniferites plexus are discussed but, given the debate surrounding the status of the genera Gonyaulax and Spiniferites, no formal taxonomic reassignments are proposed. These observations confirm that establishing cultures of cyst taxa in problematic dinoflagellate groupings and meticulous high-resolution scanning electron microscopic observation of the specimens have great potential for elucidating cyst–theca relationships and clarifying dinoflagellate taxonomy.