A new raphid pennate diatom genus, Eunophora, and three new species are described from highland lakes and streams in Tasmania and New Zealand. Eunophora tasmanica and E. indistincta are only found in Tasmania; E. oberonica and a fourth species (Eunophora sp. 1) also occur in New Zealand. The presence of polar rimoportulae in E. tasmanica and E. oberonica, the relatively simple structure and arrangement of the raphe system and the stria pattern indicate that Eunophora belongs to the subclass Eunotiophycidae. However, it differs from the other genera in this subclass in the amphoroid symmetry of the cells, the length of the raphe slits and the non-coaxial internal central raphe endings; also unusual are the position of the raphe on the valve face instead of on the ventral mantle and the presence of many small discoid or band-like chloroplasts. Eunophora may represent a link between the Eunotiophycidae and the amphoroid genera of the Bacillariophycidae. Eunophora is characteristic of dystrophic to (ultra-)oligotrophic lakes and appears to be restricted to the Southern Hemisphere. The four species display a characteristic distribution in Tasmania: Eunophora tasmanica is common and widespread in all highland lakes, E. oberonica occurs mainly in the dystrophic western lakes, while E. indistincta and Eunophora sp. 1 were found mainly in intermediate lakes along the limnological corridor between the western dystrophic lakes and the eastern oligotrophic lakes.

Phylogenetic analyses of the Dasyaceae based on sequence analysis of the large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (rbcL) and 42 morphological characters are presented. Comparative sequence analysis confirms the general view of the Ceramiaceae as a primitive, paraphyletic group giving rise to the Rhodomelaceae, Delesseriaceae and Dasyaceae within the monophyletic Ceramiales. On the basis of both data sets, the Heterosiphonia-like genera (Heterosiphonia, Colacodasya and Dasyella) are the most primitive members of the Dasyaceae, whereas the Dasya-like genera (Dasya, Pogonophorella, Eupogodon and Rhodoptilum) and Thuretia and Dictyurus are of more recent origin. On the basis of morphological data only, Thuretia and Dictyurus form a sister group to Heterosiphonia, and Eupogodon is monophyletic whereas Dasya and Heterosiphonia are not. Primary radial symmetry has arisen once in the Dasya clade but is secondarily obscured in some species by heavy, asymmetrical cortication that gives the appearance of bilateral symmetry. This is illustrated by species of Eupogodon and Rhodoptilum.

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.

Cells of the potentially toxic dinoflagellate Alexandrium catenella have a complement of features typical of dinoflagellates, including dinokaryon, pusule and amphiesma. No endosymbiotic bacteria were found in the Californian strain examined, which is weakly toxic. The chloroplast consists of a central pyrenoid complex with radiating chloroplast lobes, an arrangement found also in certain other gonyaulacoid dinoflagellates. Cells are often arranged in few-celled chains and a cytoplasmic connection interconnects adjoining cells. Striated fibres line the attachment canal and also subtend the apical pore, making up an ‘apical fibrous complex’. The flagellar apparatus basically resembles that of other gonyaulacoids. However, Alexandrium catenella, Gonyaulax spinifera and Protoceratium reticulatum share the presence of two striated collar connectives and a single-stranded microtubular root associated with the longitudinal basal body, in addition to the multi-stranded root characteristic of dinoflagellates in general. Ultrastructural features indicate that these three species are closely related while Ceratium furcoides, another gonyaulacoid dinoflagellate, apparently lacks these features.

The bchI gene (synonym: chlI), whose product is involved in magnesium chelatase activity, is located in the small single-copy region of the plastid genome of Heterosigma carterae (heterokont alga, Raphidophyceae; formerly named Olisthodiscus luteus). As a unique feature, bchI in H. carterae overlaps an upstream open reading frame (ORF97) of unknown function by 23 base-pairs. Cells contain mRNAs for the full (1.6 kb) cotranscript as well as transcripts for bchI (1.2 kb) and ORF97 (0.4 kb). Transcription initiation in a plastid run on assay of the ORF97/bchI gene cluster is approximately 5-fold higher in cultures sampled in the light versus the dark. In contrast, Northern analysis shows that all three transcripts are in equal abundance at both light and dark sampling times. An antibody raised against a BchI fragment expressed in Escherichia coli recognized a protein of the expected size in the plastid fraction of H. carterae on a Western blot. Analysis of BchI amino acid sequences suggests that the protein may be membrane translocated and could bind ATP. Phylogenetic analysis of bchI sequences documents a deep evolutionary branching between chlorophyll a/b and non-chlorophyll b plastids.

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.

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 coldwater dinoflagellate Peridiniella catenata has been examined by light and electron microscopy. The fine-structure resembles that of other dinoflagellates with regard to the dinokaryon, the chloroplast enveloped by three membranes, and the pusule. The flagellar apparatus also resembles that of most other dinoflagellates. The main difference is a missing or reduced striated root connective between the longitudinal microtubular flagellar root and the transverse striated flagellar root. The amphiesma includes a scale-like layer on the outside of the plasmalemma. Another unusual feature is the presence of two distinct size classes of trichocysts, measuring c. 0.2×1 μm and c. 0.7×4 μm, respectively. In their detailed construction they resemble those of other dinoflagellate trichocysts. Peridiniella catenata differs from other gonyaulacoid dinoflagellates in the presence of chloroplasts with single-stalked pyrenoids and in details of the pusular complex. The presence of two size categories of trichocysts and the outer scale-like layer have not been observed in other gonyaulacoid dinoflagellates, indicating that P. catenata is not closely related to these dinoflagellates. However, the presence of two striated collar connectives in P. catenata, a feature hitherto observed only in gonyaulacoids, implies affinity to this group.

Populations of Cystoseira spinosa, an endemic Mediterranean brown alga, are restricted to deep water at undisturbed sites. The species composition of an old stand in the Scandola Marine Reserve (Corsica) at a depth of 26–29 m reflects the dominance of Cystoseira spinosa over other brown and red algae, with an average biomass of 450 g dw m−2, and a mean density of 28.8 plants m−2. The length of the main axis was chosen as a convenient parameter related to size. The number of secondary axes increases exponentially with the length of the main axis, suggesting the existence of environmental constraints (possibly hydrodynamism), which may impose severe restrictions on the unlimited growth of the main axis. The size pattern of the Cystoseira spinosa plants from the population studied showed a log-normal distribution, with the highest frequency within size classes of 9–15 cm (main axis length), and a maximum size of 44 cm. Areas devoid of adult Cystoseira plants and lacking other erect algae had a significantly higher (8%) number of recruits than undisturbed areas. We suggest that the log-normal size distribution found in the population studied is due to an inhibition of recruitment by erect algae, and that disturbances that remove these algae are necessary to increase Cystoseira recruitment.

A new large DNA virus (PlitV-1) infects the marine filamentous brown alga Pilayella littoralis. It was collected in Alaska and infects other P. littoralis isolates of different geographic origin. The virus has an icosahedral capsid of c. 161 nm in diameter, enclosing an electron-dense core. The genome consists of double-stranded DNA and is approximately 280000 base pairs in size. The virus is latent in somatic cells of the host and is propagated only upon induction of the host's reproductive organs. It causes deformed sporangia, resulting in infertility, and is structurally similar to other brown algal viruses. PCR amplification of a genomic sequence coding for part of a structural glycoprotein of the Ectocarpus siliculosus virus EsV-1 produced a fragment of similar size to that obtained with EsV-1.

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.

The habitat of the acido- and thermophilic red algae Galdieria sulphuraria and Cyanidium caldarium was examined in acidic hot sulphur springs in the vicinity of Naples (Italy). These species grew on soil and rocks, but a large part of the populations was cryptoendolithic. The endolithic algal layer (1–3 mm in thickness) was covered by amorphous silica (1–2 mm in thickness) containing traces of hydrotroilite (FeS.nH2O) and elemental sulphur. Organotrophic bacteria and fungi were not found in the algal layer. Light penetration measurements showed that 0·1–1% of the sunlight reached the upper part of the algal layer. Thus, low-light-adapted algae should be able to perform some photosynthesis in this endolithic habitat. Under conditions where light is even more limited, e.g. in winter or after darkening of the covering layer, many of the cells might not survive. Aqueous extracts of these algae are excellent growth substrates for Galdieria sulphuraria. Therefore, we propose that compounds released from dead cells in the endolithic layer are used by the surrounding Galdieria cells for heterotrophic metabolism. This would increase their chance of surviving prolonged periods under detrimental conditions.

Nitrogen (N) and phosphorus (P) limitation affect the photosynthetic apparatus of Dunaliella tertiolecta in markedly different ways. When grown at 0·25 d−1 (18 % of the resource-saturated maximum rate, μmax=1·39 d−1) in chemostat cultures, N- and P-limited cells were chlorotic relative to nutrient-replete controls. The lutein-to-chlorophyll a ratio increased under both N and P limitation, whereas the neoxanthin-to-chlorophyll a ratio increased only under P limitation. The ratio of accessory photoprotective pigments (α- and β-carotene) to chlorophyll a increased under N-limited conditions. Despite differences in accessory pigment complement, chlorophyll a-specific light absorption coefficients of N- and P-limited cultures did not differ significantly, and were greater than in nutrient-replete conditions. In contrast, the initial slope of the photosynthesis–irradiance (PE) response curve (αChl) declined under nutrient-limiting conditions. There were slight reductions in the maximum quantum efficiency of photosynthesis (ϕm) in N- and P-limited cells. Reductions in ϕm were accompanied by reductions in the ratio of variable to maximum fluorescence (Fv/Fm), and the ratio of the photosystem II reaction centre protein D1 to the large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). Differences in light-saturated gross photosynthesis rate, as measured by light/dark oxygen exchange, could be accounted for by changes in the abundance of the carboxylating enzyme Rubisco. Oxygen exchange and 14CO2 assimilation appeared to measure different processes in P-limited and N- limited cultures. At light-saturation, 14C-bicarbonate assimilation approximated gross photosynthesis (as measured by light/dark oxygen exchange) in P-limited cultures. In contrast, 14C-bicarbonate assimilation approximated net photosynthesis in N-limited cultures. When all culture conditions were compared, there was linear covariation of the rates of reductant supply via light absorption and photochemical charge separation with the rates of reductant demand for CO2 fixation and NO3− reduction.

The influence of temperature and light on growth and photosynthetic physiology were investigated in embryos of Fucus evanescens grown at 5 or 20°C under irradiances of 15 or 150 μmol photons m−2 s−1 for 7–10 days. Growth was light-independent, but high-temperature embryos were always significantly larger than those grown at low temperature. Photosynthesis-irradiance responses were measured at growth temperature and a standard temperature (20°C) to isolate instantaneous effects of temperature from acclimation responses. Our data indicate that growth and photosynthesis are uncoupled during the early development of Fucus, and that acclimation of the photosynthetic light-harvesting apparatus occurred. Light-limited net photosynthesis (Psub-sat) responded similarly to high temperature and low light. Rates of Psub-sat were similar in embryos grown at 20°C (regardless of light) and at 5°C in low (c. 1.2 nmol O2 mm−3 min−1), whereas those of 5°C high-light embryos were lower (c. −0.04 nmol O2 mm−3 min−1). Changes in Psub-sat were associated with changes in initial slope of the photosynthesis-irradiance curve (α) and dark respiration. Differences in α were attributed to increased absorption due to increased chlorophyll a content and PSII reaction centre densities. Changes in α were also correlated with changes in fluorescence induction kinetics, with high-temperature and/or low-light embryos exhibiting higher ratios of variable: maximum fluorescence (Fv/Fm) than 5°C high-light embryos (c. 0.5 vs. 0.19). In contrast to Psub-sat, changes in light-saturated photosynthesis (Pmax) in response to growth under different temperature/light regimes did not confer metabolic compensation. Rates of Pmax were highest in 20°C high-light embryos (7.3 nmol O2 mm−3 min−1), lower in 20°C low-light and 5°C low-light embryos (c. 2.6 nmol O2 mm−3 min−1) and lowest in 5°C high-light embryos (2.3 nmol O2 mm−3 min−1). We suggest that the ability to achieve temperature-independent rates of Psub-sat may be important for fucoid embryos that recruit in intertidal microhabitats where photosynthesis is often light-limited.

Small-subunit ribosomal DNA (SSU) sequences for 14 members of the rhodophyte order Acrochaetiales were used to generate phylogenetic trees to determine whether the Acrochaetiales is monophyletic and to assess the relationships of acrochaetioid algae to closely related taxa. Within the Acrochaetiales, two strongly supported groups are recognized: one group that includes, in addition to three other species, the type species of the genera Acrochaetium, Audouinella and Rhodochorton; and a second group that includes an unequivocal representative of Colaconema and nine additional species. The relationships of these groups with the Batrachospermales, Palmariales and Nemaliales were not resolved and the possibility that the Acrochaetiales is polyphyletic was not eliminated. Resolution of relationships for species within these groups was strong in only a few cases, with many of the phylogenetic issues at this level remaining equivocal. Our results do not position Camontagnea in the Acrochaetiales, as has recently been suggested, but strongly ally this genus to the family Rhodothamniellaceae of the Palmariales. The phylogenetic position of Rhododraparnaldia, an alga intermediate between the Acrochaetiales and Batrachospermales, remains unresolved. These molecular results provide a foundation for assessing the taxonomic significance of phenotypic characters (e.g. anatomy, life histories, morphology, phycoerythrin type and plastid details) variously considered taxonomically significant in the Acrochaetiales.

Effects of nitrogen (N) and phosphorus (P) limitation on calcification and coccolith production in Emiliania huxleyi were investigated in batch and chemostat cultures by means of chemical analyses of calcium (Ca) and organic carbon (C), counts of coccoliths and cells, and scanning electron microscopy. In a normally calcifying (C-cell) clone growing in the absence of nutrient limitation in batch or semi-continuous cultures, c. 36 attached plus detached coccoliths were present per cell. In batch cultures as well as in chemostats, the number rose to 70–120 when either N or P became strongly limiting. The molar Ca/C ratio, measured in chemostats, showed a corresponding increase from 1·07 to c. 1·38. The two types of limitation had opposing effects on the calcification of individual coccoliths: the mean Ca content of a coccolith decreased from a normal value of 0·60 pg to 0·46–0·49 pg under N limitation, and increased to 0·67–0·73 pg under P limitation. These effects were accompanied by corresponding modifications of coccolith morphology. In batch cultures of one naked (N-cell) clone grown to the stationary phase, P limitation but not N limitation induced the formation of c. 40 coccoliths per cell; these coccoliths were of aberrant shape. In another N-cell clone, P limitation had no such effect. The results suggest on one hand that coccolith formation is generally less dependent on N and P nutrients than is cell replication, and on the other hand that stages exist in the growth and calcification of a coccolith that are specifically influenced by either N- or P-containing cell constituents.

In the red alga Bostrychia moritziana, release of spermatia is triggered by slight osmotic shock; they emerge under pressure apparently generated by swelling of the mucilaginous sheath. Spermatia adhere tenaciously to trichogynes of the carpogonium. Adhesion triggers spermatial mitosis, which is complete in about 30–45 min; there is no cytokinesis and the binucleate spermatium becomes vacuolated. The delicate, dynamic trichogyne cytoplasm contains complex membranous components and vacuoles. At the contact zone, the trichogyne and spermatial wall erode, forming a pore, and cytoplasmic continuity (plasmogamy) is achieved after about 50–70 min. Many trichogynes rupture during these events because of inadequate structural connection with the spermatia. Normally, both spermatial nuclei enter the trichogyne in sequence; rarely, both nuclei enter together. Entrance is rapid, and the nuclei often become thin and greatly elongated as each squeezes through the narrow pore into the trichogyne. Once inside, each nucleus resumes its normal shape as it starts to move steadily along the trichogyne, often with irregular pauses. One nucleus of each pair (not necessarily the first out of the spermatium) migrates along the trichogyne towards the carpogonium base to fertilize the female nucleus; the other moves in the opposite direction, away from the entry site, and it often ends up near the tip of the trichogyne. This same scenario was observed for each of several spermatia contributing nuclei to one trichogyne. Thus, our observations indicate that the two nuclei in each spermatium are differentiated so that only one is capable of fertilization, differentiation being visibly expressed in the direction that the nucleus moves as it enters the trichogyne.

Four populations of the newly described freshwater red algal species Batrachospermum spermatoinvolucrum were sampled from British Columbia on the west coast of North America and Labrador on the east. The rDNA internal transcribed spacer (ITS) 1 and 2 sequences, RUBISCO large subunit (rbcL) gene data for three of the populations and morphometric characteristics were compared with those of B. gelatinosum. In addition, the key feature distinguishing B. spermatoinvolucrum, spermatangia on the involucral filaments of the carpogonial branch, was investigated seasonally in one British Columbia population of this species. The ITS analysis suggested that the B. spermatoinvolucrum populations were more closely related to particular B. gelatinosum populations than to each other and did not form a monophyletic clade. Two populations of B. spermatoinvolucrum from Labrador and British Columbia had identical rbcL sequences that were distinct from that of B. gelatinosum. However, the rbcL sequence from the third population of B. spermatoinvolucrum differed by only one nucleotide substitution from the B. gelatinosum populations. The tree generated from the morphometric data showed two groupings, each containing populations of both taxa. The presence of spermatangia-bearing involucral filaments was a stable character throughout the year. On the basis of these findings, B. spermatoinvolucrum is reduced to a form of B. gelatinosum. This form would encompass variant populations with characteristic carpogonial involucral filaments bearing spermatangia.

The marine red alga Ahnfeltiopsis triquetrifolia sp. nov. (Phyllophoraceae, Gigartinales) is described from Japan. Foliaceous unisexual gametophytes are characterized by having three-edged axes, and crustose tetrasporophytes are distinguished by the following combination of features: tightly coalescent perithallial filaments, nemathecial sori, small numbers of both tetrasporangia (3 or 4) and sterile cap cells (1 or 2) in each fertile filament, and the absence of hypobasal tissue. Gonimoblast filaments develop from the auxiliary cell after it has fused with a carpogonium. Carposporangia develop from gonimoblast cells, from medullary cells contacted by the gonimoblast filaments, and from the cells produced by such medullary cells. Mature, compact cystocarps are immersed within the medullary layer and discharge carpospores through carpostomes formed in the thickened cortex. Cultured tetrasporophytes were induced to sporulate by transfer from a long-day to a short-day regime at 20°C, and one single short-day cycle was effective for tetrasporangial induction. Tetraspore germlings gave rise to basal discs from which upright axes developed. The upright axes showed a morphology similar to that of field-collected gametophytes, although they remained vegetative during 18 months in culture.

A new method of releasing cellular soluble organic matter from microalgae is reported. This method, which could be used to help characterize the production and taxonomic composition of a phytoplankton bloom, was developed in the laboratory to determine the transition temperature, Tm, for planktonic algae. The Tm of these algae is defined as the temperature at which half the cellular soluble carbon is found extracellularly under standard conditions, by analogy with the definition of Tm in bacteriology. Values of Tm in the range of 23–46·5 °C are reported for six species of Bacillariophyceae (diatoms) and two species of Prymnesiophyceae. Species-specific Tm values are highly reproducible and are regarded as an intrinsic property of the species and its physiological races. Possible field uses of the method are discussed.