Cyanobacteria are often the dominant phototrophs in high-latitude lakes and streams where they must experience continuously low temperature and extreme variations in daylength. The present study examined the interaction between these two variables for the growth and physiology of an Arctic isolate of the mat-forming species Schizothrix calcicola (Agardh) Gomont. Growth rates (μ), photosynthesis (P), respiration (R), pigment composition and in vivo absorption characteristics were measured under 15 combinations of daylengths (8[ratio ]16, 12[ratio ]12, 16[ratio ]8, 20[ratio ]4 and 24[ratio ]0 L/D) and temperatures (5, 15 and 25 °C). μ increased with increasing temperature (μmax at 5 °C = 0·12 d−1, μmax at 25 °C = 0·28 d−1) and a similar trend was observed in photosynthetic capacity (average PBmax at 5 °C = 4·42 mg C (mg Chl a)−1 h−1, average PBmax at 25 °C = 5·74 mg C (mg Chl a)−1 h−1), pigment content and absorbance. Daylength had a positive effect on μ and pigment absorption, but not pigment content. The shape of the μ–daylength curve varied with temperature: μ was a linear function of daylength at 5 °C, but at 15 and 25 °C the relationship resembled a rectangular hyperbola and μ saturated at 16[ratio ]8 and 12[ratio ]12 L/D, respectively. The non-linear relationship between μ and daylength at high temperature was related to a reduction in net photosynthesis under extended daylength; at 25 °C, net P under 24[ratio ]0 L/D was 0·82±0·37 mg O2 (mg Chl a)-1 h−1, while under 8[ratio ]16 L/D, it was 6·54±0·69 mg O2 (mg Chl a)−1 h−1. The constant increase in growth with increasing daylength at low temperature may reflect an adaptive tolerance to the combination of cold temperature and continuous daylight during the Arctic summer.

The brown macroalga Laminaria saccharina exhibits a type of HCO3− utilization that could be almost completely inhibited either by proton buffers or by acetazolamide, an inhibitor of extracellularly operating carbonic anhydrase. This means of HCO3− utilization featured properties similar to direct HCO3− uptake in that photosynthetic rates were proportional to the HCO3− concentration of the seawater over a wide pH range (pH 7·0–9·5). Despite this, it must be characterized as carbonic anhydrase-catalysed external HCO3− dehydration and not as direct HCO3− uptake. A mechanism is suggested involving a CO2-concentrating capability located at the cell membrane. This mechanism, which might be common in brown algae, is suggested to have an adaptational advantage in colder regions of the sea (as compared with the direct HCO3− uptake of green macroalgae). This means of HCO3− utilization is inhibited even by fairly low concentrations of buffer, with consequences for the interpretation of earlier experimental studies on L. saccharina (and possibly other brown algae). These consequences relate both to ecology (e.g. determination of inorganic C affinity) and physiology (e.g. assessing mechanisms for inorganic C uptake).

Single-stranded conformational polymorphism (SSCP) analysis of Rubisco spacer plastid haplotypes was used to assess population differentiation in the mangrove-dwelling red alga Caloglossa leprieurii (Montagne) J. Agardh. Over 1000 samples from 16 populations in northern and eastern Australia were scored with SSCP. Seven haplotypes were discovered, three of which were only found in single populations. The haplotypes formed three phylogenetically distinct lineages. A haplotype found only in north Australia (haplotype N) has closer affinities with a haplotype previously found in Japan than with any other Australian haplotypes. One haplotype (B) was dominant in northern populations and another (C) was dominant in southern populations. Haplotype A was found in geographically intermediate populations but never in high abundance ([les ] 10%). Population analysis of haplotype frequencies revealed that many populations were significantly differentiated from each other. These data indicate that populations of C. leprieurii in Australia are genetically isolated from each other, as many individual populations, probably due to limited gene flow.

Twenty-one marine and freshwater specimens of Hildenbrandia from Europe were compared by analyses of morphometric data and sequences of the rbcL chloroplast gene (which codes for the large subunit of the ribulose-1,5-bisphosphate carboxylase/oxygenase enzyme) and the nuclear 18S ribosomal RNA (rRNA) gene. Eleven freshwater specimens, all corresponding to H. rivularis, were collected from the British Isles, Germany, France, Austria, Spain and Italy. Six marine specimens, representing H. rubra, were obtained from Northern Ireland, Wales, France, Norway, Sweden and the Netherlands, while four marine specimens, corresponding to H. crouanii, were collected from Scotland and Germany. Morphometric analyses of vegetative and reproductive characters distinguished three groups of specimens, which correspond to the three species. Parsimony and distance analyses of the rbcL and 18S rRNA genes were performed on these samples and sequences of North American representatives were included to determine their inter-relationships. The rbcL gene sequence analyses separated the marine and freshwater specimens, with the H. rivularis and H. angolensis representatives forming a well- supported monophyletic clade. The rbcL sequence analyses did not resolve the groupings of marine specimens determined in the morphometric analysis. Analyses of the 18S rRNA gene sequences also supported separation of the marine samples from freshwater samples, although the bootstrap and decay support was not as strong as for the rbcL gene. H. rubra formed a monophyletic clade that was weakly supported. In terms of biogeographic trends, the fairly low intraspecific divergence of H. rivularis (0–1·9% for the rbcL gene and 0–3·6% for the 18S rRNA gene) and the positioning of these samples in the gene trees supports the concept that they are derived from marine populations.

Three sand-dwelling species of the marine dinoflagellate genus Sinophysis were examined from intertidal and subtidal North German Wadden Sea sand and are illustrated by light and scanning electron microscopy. Two are described as new: S. stenosoma sp. nov. and S. grandis sp. nov. Sinophysis stenosoma sp. nov. is compressed laterally with a cell size of 37–56 μm long and 21–33 μm wide, a length/width ratio of 1·43–1·89, an epitheca width (dorsoventrally) of 5·5–8·0 μm, and a sulcus length of about half the cell length. Sinophysis grandis sp. nov. is compressed laterally with a cell size of 50–59 μm long and 35·0–41·5 μm wide, a length/width ratio of 1·29–1·61, an epitheca width (dorsoventrally) of 12–17 μm, and a sulcus length of about three-quarters the cell length. The third species, Sinophysis ebriolum (Herdman) Balech, is the most common species in the Wadden Sea. All species occur throughout the year and are all sand-dwelling, non-photosynthetic, with a smooth theca. They can be distinguished by size, length/width ratio, epitheca size, relative sulcal length and thecal pore pattern. A key to the five known Sinophysis species is provided.

A phylogenetic analysis was conducted on 21 biraphid naviculoid diatom species (from three orders and five families, using 5 protoplast and 21 frustule characters) to test whether the recently described genus Craspedostauros was more closely related to members of the Mastogloiaceae or to other stauros-bearing diatoms. The analysis also tested, and confirmed, the hypothesis that the stauros, as recognized by light microscopy, is a homoplastic character. Whereas partitioned analyses of protoplast and frustule data resolved different parts of the ‘total’ tree, using NONA parsimony analysis of all the data, one tree was obtained. This tree placed Craspedostauros in the mastogloialean clade, rather than near Stauroneis, Staurophora, Haslea or Meuniera. The ordinal and familial groupings suggested by Round and others were also confirmed by the analysis, supported particularly by protoplast and some ultrastructural features.

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.

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 composition (% relative abundance) of the benthic diatom community was studied in the littoral zone (0–5 m) of the NW and E coasts of the brackish, non-tidal Gulf of Riga, in the Baltic Sea. The samples were collected concomitantly with measurements of sediment primary productivity and chlorophyll a during three cruises, representing three seasons (autumn, spring, summer). At all depths, the living diatom community was dominated by epipsammic species, the most abundant taxa being Martyana atomus, a species of Fragilariaceae and Achnanthes delicatula. The community was characterized by a stable composition and a high species diversity throughout the study period (Shannon–Weaver, mean H′ = 4·4). Principal Component Analyses (PCA), together with Redundancy Analysis (RDA) based on 129 taxa, revealed both spatial (site and depth) and seasonal differences in the diatom communities. However, these differences were mainly caused by the varying proportions of taxa common in both sampling areas in all three seasons, rather than by actual major taxonomic changes in the species present in communities. The distribution of the typical epipsammic species along the depth gradient was not uni-directional. The dominance of attached life forms, and the absence of a well-developed epipelic community, reflects the physically dynamic substratum, particularly in the eastern part of the Gulf. As a result, primary productivity is kept rather low, decreasing rapidly with depth due to frequent turbidity of the water column.

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.

A novel member of the Calyptrosphaeraceae surrounded by a hyaline sheath, with only one chloroplast and without an emergent haptonema, is tentatively described as a species of Calyptrosphaera Lohmann. It has an interrupted body to its single pyrenoid and a unique microtubular root complement with only one crystalline root (CR) nucleating on root 2 (R2). At preprophase it produces a CR1, lending support to the idea that these crystalline roots contribute to the mitotic spindle. It shares numerous ultrastructural traits with the heterococcolithophorid Cruciplacolithus neohelis but, although it is tempting to consider it a haploid phase of this organism, is distinct from it.

In this work, we attempt to quantify pulse amplitude modulated (PAM) chlorophyll fluorescence measurements in marine macroalgae in terms of photosynthetic rates. For this, the effective electron transfer quantum yield of photosystem II measured for two Ulva species, at various irradiances and inorganic carbon (Ci) concentrations, was multiplied by the estimated flux of photons absorbed by the photosynthetic pigments associated with this photosystem. The rates of electron transport (ETR) calculated in this way were then compared with rates of photosynthetic O2 evolution as measured in association with the fluorescence measurements. It was found that the calculated ETRs correlated linearly with rates of ‘gross’ O2 evolution (net O2 exchange corrected for dark respiration as measured immediately after turning off each irradiance level) within the range of irradiances applied (up to 608 μmol photons m−2 s−1). The average molar O2/ETR ratio was 0·238 for Ulva lactuca and 0·261 for Ulva fasciata, which is close to the theoretical maximal value of 0·25. Rates of O2 evolution at various concentrations of Ci also showed linear correlations with ETR, and the average molar O2/ETR ratio was 0·249. These results show that PAM fluorometry can be used as a practical tool for quantifying photosynthetic rates at least under moderate irradiances in thin-bladed macroalgae such as Ulva possessing a CO2-concentrating system. A comparison between the PAM-101 (which was used in Sweden for the light- and Ci-response measurements of Ulva lactuca) and the newly developed portable Diving-PAM (used for Ulva fasciata in Israel) showed that such fluorescence-based photosynthetic rate measurements can also be carried out in situ.

Flagellates of Haematococcus pluvialis accumulate secondary carotenoids (mainly astaxanthin and its esters) under nitrogen deficiency in combination with exposure to stronger light. Our cultivation scheme allows the characterization of metabolic activities during the accumulation process without interference by formation of the resting state (aplanospores). The highest rate of secondary carotenoid biosynthesis (0·046 h−1) was observed almost simultaneously with the highest rates of cell division (0·027 h−1) and of chlorophyll biosynthesis (0·015 h−1) after 1·5 days of exposure to nitrogen limitation and higher irradiance. Photosynthetic activity was studied by oxygen evolution and chlorophyll fluorescence measurements; changes in protein components of the photosynthetic apparatus were quantified by gel electrophoresis and immunoblot analysis. Accumulation of secondary carotenoids was accompanied by an increase in photosynthetic productivity expressed on a unit chlorophyll basis. Changes in the photosynthetic apparatus occurring mainly during the first 2 days of exposure to nitrogen limitation and stronger light can be interpreted as acclimation to the increased cultivation irradiance. Photoprotective action of secondary carotenoids as a ‘sunshade’ was demonstrated in red flagellates exhibiting a lower blue-light-induced decrease in photosystem II efficiency as compared with red actinic light.

The red algae Chondrophycus patentirameus (Montagne) Nam (‘patentiramea’) and L. paniculata (C. Agardh) J. Agardh were investigated on the basis of type material and recent collections. Both species show the following features: (i) production of two vegetative pericentral cells from each axial segment; (ii) absence of secondary pit connections between cortical cells; (iii) lack of projecting cortical cells near the apex; (iv) absence of lenticular thickenings in the walls of medullary cells; and (v) perpendicular arrangement of tetrasporangia, each of which is produced from the second pericentral cell in each fertile segment with no additional tetrasporangial pericentral cells. However, C. patentirameus has a stoloniferous holdfast, divaricate branching (with branches arising at angles up to 90°) and non-palisade-like superficial cortical cells, whereas L. paniculata has a discoid holdfast, non-divaricate branching and a palisade-like cortical layer. From this study it is concluded that C. patentirameus (here lectotypified) is distinct from L. paniculata. The latter species is here transferred to the genus Chondrophycus (Tokida & Saito) Garbary & T. Harper as follows: Chondrophycus paniculatus (C. Agardh) G. Furnari.

In this study we tested the hypothesis that iron limitation suppresses photoacclimation in cultures of the Antarctic flagellate Pyramimonas sp. The cultures were exposed to two different irradiances under iron-rich and iron-poor conditions. Light-harvesting capacity was determined by assessing the pigment composition and measuring in vivo absorption spectra. Light utilization efficiency (α) was determined from photosynthesis versus irradiance curves. The quantum yield of photosynthesis (ϕm) was calculated using α and the absorption spectra. Iron limitation led to commonly observed changes in cells of Pyramimonas, that is, a decrease in cellular pigment content and a reduction in cellular carbon and nitrogen quota. A reduction in αcell followed a decrease in ϕm and light-harvesting capacity. Interpretation of the effects of iron limitation was different when considered on a carbon basis. Because iron limitation resulted in a decrease in cellular carbon content, the carbon-specific absorption coefficient was not affected. Consequently, the observed decrease in αC was mainly due to the decrease in ϕm, showing that iron limitation did not control light utilization via pigment synthesis but exerted control on energy transfer. This is supported by the findings that at high irradiance a shift in pigment ratios within the total pool of violaxanthin, antheraxanthin and zeaxanthin towards zeaxanthin, which is indicative of photoacclimation to high irradiance, was observed for iron-replete cells as well as for iron-depleted cells. In contrast to what is generally hypothesized, the effects of iron limitation were not enhanced at low irradiance. Low irradiance led to an increase in the cellular light-harvesting pigment content. This increase was less pronounced in iron-depleted cells than in iron-replete cells. However, looking at the light-harvesting capacity of the cells on a carbon basis, it was found that iron-depleted cells responded similarly to iron-replete cells. We therefore conclude that the light-harvesting capacity was governed by light conditions and not by iron limitation. In addition to the increase in absorption capacity at low irradiance, an increase in light utilization efficiency was measured, again under both iron-rich and iron-poor conditions. Notably, the relative increase in αC was strongest in iron-depleted cells. Photoacclimation was clearly demonstrated by normalizing α to chl a. For iron-replete cells, αchl was highest at high irradiance. In contrast, for iron-depleted cells αchl was highest at low irradiance. We argue that iron-depleted cells can photoacclimate to low irradiance by a reduction in the ‘package effect’ and reducing growth rates.

Intertidal cohesive estuarine sediments frequently support extensive microphytobenthic biofilms, which are usually dominated by epipelic (motile) diatoms. The distribution of different diatom taxa varies along estuarine gradients, but it is not clear what the causative factors are in determining these patterns. In many estuaries, salinity covaries with other environmental gradients, particularly with nutrient concentrations when the river is the main nutrient source. Autecological information is required to aid interpretation of these field distributions. In this study the maximum specific growth rate (μ) and stationary phase biomass of four common taxa of estuarine epipelic diatoms (Navicula phyllepta, N. perminuta, N. salinarum and Cylindrotheca closterium) were measured in axenic unialgal cultures grown under a range of nitrogen and salinity regimes. All three Navicula species and two different clones of C. closterium showed significant differences in their response to a range of ammonium (10–4000 μM) and nitrate (10–2000 μM) concentrations across a salinity range of 10–35‰. Growth rates of N. phyllepta were significantly lower at ammonium concentrations > 400 μM, but the other three taxa showed little evidence of ammonium toxicity, even at concentrations > 1 mM. On the basis of the response of each species, the following putative ranking of preferences for inorganic nitrogen concentrations (lowest to highest, with salinity optima in parentheses) was constructed: N. phyllepta (10–20‰) – N. perminuta (10–30‰) – N. salinarum (20–35‰)/C. closterium (clone 1, 10–25‰, clone 2, 25–35‰). Such a ranking should be interpreted cautiously, as interclonal differences and adaptation to local environmental conditions can alter the preferences of taxa. These autecological data are partially supported by previously published data on field distribution, and suggest that certain taxa may have value as trophic indicator species.

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.

The genus Polysiphonia Greville, nom. cons., has had a long and confused nomenclatural history. At present, Polysiphonia has a wide circumscription, including at least 200 species, but it is heterogeneous in many vegetative and reproductive developmental features. Central to any re-evaluation of the genus is a detailed examination of the type species of Polysiphonia, P. urceolata (Lightfoot ex Dillwyn) Greville, which is conspecific with P. stricta (Dillwyn) Greville. We here report on the vegetative and reproductive morphology of P. stricta, including P. urceolata, based on type and other material from the British Isles. Thalli consist of prostrate and erect ecorticate axes with four pericentral cells, attached by unicellular rhizoids remaining in open connection with pericentral cells. Prostrate axes lack vegetative trichoblasts; trichoblasts occur seasonally on erect axes. Branch initials are cut off from the subapical cell at intervals of four or five segments in dichotomous and alternating pairs rather than being formed from each axial cell in the spiral pattern typical of most species of Polysiphonia. Spermatangial branch initials, which are trichoblast homologues, are produced directly from each axial cell at the tips of erect branches, not subtended by trichoblasts, and have two- to five-celled sterile tips when mature. The mature carpogonial branch is four-celled with a two-celled first sterile group and a one-celled second sterile group. Following presumed fertilization, direct fusion apparently takes place between carpogonium and auxiliary cell; mature cystocarps are usually urceolate. Tetrasporangia are formed from the third pericentral cell, in straight series, and have two pre-sporangial cover cells. Previous accounts of a third, post-sporangial cover cell could not be substantiated. P. stricta and a small group of other Polysiphonia species differ in several important respects from most members of the genus, which have rhizoids cut off from pericentral cells by a cell division, abundant trichoblasts, spirally arranged tetrasporangia and a post-sporangial cover cell. The branching pattern of P. stricta highlights the difficulties of distinguishing between the tribes Polysiphonieae and Pterosiphonieae.

The effect of copper additions (Cu ranging from 0 to 30 μM) on the photosynthesis of three different microalgal biofilms was studied to identify the factors that cause sensitivity differences between benthic and pelagic algae. The response of biofilms which colonized artificial substrata in the River Meuse was compared with those of two laboratory-grown monospecific biofilms, one consisting of the diatom Synedra ulna, and the other composed of a filament-forming cyanobacterium, Oscillatoria sp. The photosynthetic yield ΦII (quantum efficiency of photosystem II) was studied with PAM (Pulse Amplitude Modulated) fluorimetry. S. ulna biofilms appeared to be the most sensitive to Cu, followed by the cyanobacteria, while natural biofilms, dominated by supposedly very sensitive diatom species such as Melosira varians and Diatoma vulgare, were the most resistant to Cu. In the highly productive biofilms, pH is suggested to play a role in lowering toxicity by helping the precipitation of cupric ions. Cu accumulation by the biofilms during the exposure period followed a linear relationship with Cu concentration, saturation not being observed; natural biofilms had an accumulation factor of 1–2·5 × 103 relative to the concentrations in the water, while the diatoms growing unattached to the substratum had a higher concentration factor, up to 4·9 × 103. It was concluded that the physical structure of the biofilm (package of cells and thickness), and not the species composition, was the main factor regulating the sensitivity of the biofilm to Cu toxicity during short-term exposures.