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.

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

The effect of copper on carbohydrate production in the diatom Cylindrotheca fusiformis and in the dinoflagellate Gymnodinium sp. was examined in batch cultures. Copper was shown to inhibit the growth of the two species to different extents: in particular the dinoflagellate was highly sensitive to the metal when metal chelators were absent. Analysis of the carbohydrate content showed that C. fusiformis produced a much higher total amount than Gymnodinium sp. and cells of the diatom which were exposed to toxic copper concentrations displayed a higher carbohydrate production which paralleled the increase in copper concentrations. The increased production could be attributed to extracellular rather than to intracellular carbohydrate and it occurred after 12 and 16 days of growth, respectively, for cells exposed to 0·2 and 0·5 mg l−1 Cu. The response of carbohydrate production by Gymnodinium sp. to the presence of copper was much smaller and occurred only in late stationary phase of growth (21st day). An analysis of the copper content showed that the amount of metal accumulated by Gymnodinium sp. was similar to that absorbed by C. fusiformis, but it was a larger fraction of the quantity supplied. The results presented indicate that carbohydrate extrusion is one of the mechanisms which may prevent toxic effects due to the presence of copper in the culture medium.

Seventeen species of the mainly sand-dwelling genus Amphidinium are reported from south-eastern Australian waters. Three new species are described: A. boggayum, A. mootonorum and A. yuroogurrum. Additional features from previously described species are presented, including non-motile cell stages. Nine of these species are new records for Australia; however, these species are probably widespread and common. Two potentially ichthyotoxic species of Amphidinium were commonly found: A. carterae and A. cf. operculatum. A table of morphological characters is compiled as a step towards recognizing new characters with which to group species of this presently artificially defined unarmoured dinoflagellate genus.

Secondary structure analysis of 34 internal transcribed spacer 2 (ITS-2) sequences showed that the current model for the green algae Scenedesmus and Desmodesmus is not accurate. In particular, helix I of the currently used model showed considerable deviations from our new model. The newly proposed model is supported by many two-sided compensated base pair changes and fully compensated insertions in all four helices. Phylogenetic analysis by maximum parsimony based on the new alignment confirmed the recent division of the old genus Scenedesmus into the new genera Scenedesmus and Desmodesmus. However, the analysis was not able to show phylogenetic relationships within these two genera. Hence, the ITS-2 region alone is not suitable for clarifying the phylogeny of Scenedesmus and Desmodesmus and new regions have to be found for future sequence analyses.

The utility of rDNA internal transcribed spacer (ITS) sequences for separating species of Ulva along the North Brittany coast of France was investigated. Particular attention was paid to the Ulva species responsible for ‘green tides’. Floating thalli are difficult to identify due to fragmentation and it was not clear at the outset whether one or more species of Ulva might be contributing to the green tide phenomenon. Results show that ITS sequences are good markers for Ulva species and that the Lannion Bay green tide taxon is a previously unrecognized species that can also be identified on morphological grounds. We found that ITS type did not necessarily correspond to the initial identification of a specimen based on morphological features, due to the lack of good diagnostic characters. This survey highlights the need for a more intensive survey of Ulva populations along European coasts. Once ITS groups can be recognized, quick screening assays can be developed to aid morphological identification.

We report here the complete sequence of the mitochondrial genome of the brown alga Laminaria digitata (Hudson) J.V. Lamouroux. L. digitata mtDNA is a circular molecule of 38,007 bp (64·9% A+T), encoding 63 genes and 3 ORFs and with only 6·7% of non-coding sequences. Based on gene content and order, its overall organization is very similar to that of the mitochondrial genome of Pylaiella littoralis, another brown alga belonging to a different sublineage of the Phaeophyceae. In particular, the two genomes share unusual features, which hence could be unique to brown algae among the heterokont lineage, namely the presence of a rn5 gene, a short nad11 gene, a cox2 gene with a large in-frame insertion and α-proteobacterial-like promoter sequences. On the other hand, L. digitata lacks the sequences which are thought to have been transmitted horizontally to the P. littoralis genome, that is, the group-II introns in the rnl and cox1 genes, and it features only traces of an ancestral T7-like RNA polymerase. Distance phylogenetic trees inferred from concatenated mitochondrial genes confirm that speciation of brown algae occurred recently compared to other heterokonts.

The coenocytic green alga Caulerpa racemosa colonized the Mediterranean some time after the opening of the Suez Canal in 1869. For most of the past century it has remained confined to the southeastern Mediterranean, but over the past several years the species has been reported in abundance along the western coasts of Italy, Sardinia and the Marseille area of southern France. Whether this constitutes a natural range expansion or a possible new introduction is under discussion. The purpose of this study was to establish the ITS signatures of populations inside and outside the Mediterranean. ITS1 sequences were compared among 78 clones from 21 individuals representing 11 populations of C. racemosa, collected from the Western Mediterranean, the Canary Islands, Panama and Western Australia. Intra-individual polymorphism of ITS1 was found to be as high or higher than inter-individual polymorphism across all samples tested. Polymorphism parsimony analysis, which takes into account intra-individual variation, revealed strong separation between individuals from Panama, Fuerteventura (Canary Is.) and the Mediterranean. In contrast, none of the six Mediterranean populations could be distinguished from one another. In addition, individuals and their clones collected from Perth (Australia) and Gran Canaria were spread throughout the Mediterranean clade. Possible reasons for the lack of homogenization of ITS arrays in C. racemosa under the mechanisms of concerted evolution and implications for phylogeographic interpretation are discussed and compared with Caulerpa taxifolia.

Haslea ostrearia, the peculiar diatom that develops in oyster-ponds and synthesizes a water-soluble blue pigment (marennine), was grown in a semi-continuous mode over a wide range of irradiances (20–750 μmol; m−2 s−1). Growth, photosynthesis and pigment content were determined for algae maintained in exponential growth phase by regular dilution with fresh medium. Increasing the growth irradiance resulted in a decrease in the chloroplast length, but had no clear influence on the size of the cellular compartments pigmented by marennine accumulation. Growth rates increased with irradiance from 20 to 100 μmol; m−2 s−1 and were constant from 100 to 750 μmol; m−2 s−1. Increasing growth irradiance caused a decrease in the cellular content of chlorophylls a and c and fucoxanthin, in contrast to diadinoxanthin. Algae acclimated to high irradiance had lower maximum photosynthetic rate (Pnm) and maximum light utilization coefficient (α) when expressed on a per cell basis. On a chlorophyll a basis, the higher the growth irradiance, the lower the maximum light utilization coefficient and the higher the maximum photosynthetic rate. No photoinhibition was observed at irradiances up to 1500 μmol; m−2 s−1 whatever the growth irradiance. In vivo chlorophyll a fluorescence showed that cells grown at high irradiance had effective photosystem II quantum efficiency (measured at the growth irradiance) considerably lower than that of cells grown at low irradiance. Thus H. ostrearia withstands high light exposure, consistent with the observation that this alga can outcompete other diatoms encountered in oyster-ponds characterized by low turbidity and shallow depth.

Photoinhibition of photosynthesis in the red alga Chondrus crispus from different shore levels was investigated under laboratory and field conditions. The underwater light climate at Roscoff (French Atlantic coast), characterized by transmittance spectra, was shown to be intermediate between Jerlov coastal type 1 and oceanic type III. Chondrus crispus thalli were collected at four depths (3·5–8·5 m below high tide level) and exposed to daily courses of artificial and natural light. Filters were used to discriminate between the effects of photosynthetically active radiation (PAR) and ultraviolet radiation (UVR) under the photoinhibitory treatments. In the presence of natural UVR, photoinhibition at midday was increased by up to 60%. Recovery from photoinhibition was measured at different times throughout the light stress. Recovery kinetics differed between morning and early afternoon in all treatments, and were dependent on the light dose. Whereas biphasic kinetics were observed in all treatments in the morning, the recovery in early afternoon was significantly slower. The influence of UVR on recovery was apparent after exposure to higher light doses. In all investigations, sensitivity to photoinhibition corresponded to zonation of the algae, with deeper-growing algae showing a greater depression of fluorescence yield, and slower recovery (indicating acclimation to the growth irradiance). An increase in the phycoerythrin content and increasing photosynthetic efficiency with increasing growth depth were observed.

The toxic spill of acid wastes rich in heavy metals/metalloids (AWHM) from the Aznalcóllar mine in April 1998, threatening the Doñana National Park, is considered to be the worst environmental disaster related to acute pollution in Spanish history. The aim of this work was to study the adaptation of microalgae (which play an important role as primary producers) from AWHM sensitivity to AWHM resistance by using the alga Scenedesmus intermedius as an experimental model. The Malthusian parameter (m) and the carrying capacity (K) were reduced by mud and soil samples collected from the affected area. A dose–effect analysis showed that fitness progressively diminished with increasing sample concentration. A fluctuation analysis demonstrated that AWHM-resistant cells arose by rare spontaneous mutations that occurred randomly prior to the incorporation of the AWHM. The rate of spontaneous mutation from AWHM sensitivity to AWHM resistance was 2.12×10−5 mutants per cell division. A competition experiment between wild-type AWHM-sensitive cells and AWHM-resistant mutants showed that in small populations the AWHM-resistant mutants are driven to extinction in the absence of selection for AWHM resistance. The resistant phenotypes are maintained in the absence of AWHM as the result of a balance between spontaneous mutation and natural selection, so that about 43 AWHM-resistant mutants per million cells are present in the absence of AWHM. Our experimental model suggests that mutation is essential for adaptation of microalgal populations to environmental changes. Rare spontaneous pre-adaptive mutation is enough to ensure the survival of microalgal populations in contaminated environments when the population size is large enough.

Photosynthetic responses of rewetted Nostoc flagelliforme to CO2, desiccation, light and temperature were investigated under emersed conditions in order to characterize its ecophysiological behaviour in nature. Net photosynthesis increased to a maximum rate at about 30% water loss, then decreased, while dark respiration always decreased with the progress of desiccation. Light-saturated photosynthesis and dark respiration were significantly reduced at 8 °C, but remained little affected by changes of temperature within the range of 15–35 °C. Photosynthetic efficiency (α) was maximal at the beginning of desiccation and then reduced with increased water loss. Saturating irradiance for photosynthesis was about 194–439 μmol quanta m−2 s−1, being maximal at about 30% water loss. No photoinhibition was observed at irradiances up to 1140 μmol m−2 s−1. Light compensation points were about 41–93 μmol m−2 s−1. Photosynthesis of N. flagelliforme was CO2-limited at the present atmospheric CO2 level. The CO2-saturated photosynthesis increased with increase of irradiance (190–1140 μmol m−2 s−1) and temperature (8–25 °C) and decreased significantly with water loss (0–75%). Photosynthetic affinity for CO2 was sensitive to temperature and irradiance. The CO2 compensation point (Γ) increased significantly with increased temperature and was insensitive to irradiance. Desiccation did not affect Γ values before water loss exceeded 70%. Photorespiratory CO2 release did not occur in N. flagelliforme at the current atmospheric CO2 level.

Eight Cocconeis Ehrenberg taxa (species and varieties) epiphytic on the leaves of Posidonia oceanica (L.) Delile were studied by scanning and transmission electron microscopy. Samples of Posidonia oceanica were collected throughout the year from seagrass meadows around the island of Ischia (Gulf of Naples, Italy). On the basis of some peculiar ultrastructural characteristics of the valve areolation, a new species, Cocconeis multiperforata sp. nov., and two new varieties, C. neothumensis var. marina var. nov., and C. scutellum var. posidoniae var. nov., are described. Ultrastructural analysis also revealed new morphological characteristics in C. britannica Naegeli in Kützing and C. maxima (Grunow) Peragallo & Peragallo, and confirmed observations of other authors for C. molesta var. crucifera Grunow, C. pellucida Grunow in Rabenhorst and C. stauroneiformis (Rabenhorst) Okuno. Our observations on the abundance of the different species provide new information on their distribution and ecology.

Chrysochromulina and Prymnesium are important bloom-forming organisms in marine and brackish waters, respectively. Both genera include toxic species, which are primarily implicated in fish kills. Previous analyses of small subunit (SSU) rDNA sequences from Chrysochromulina and Prymnesium spp. indicate that Chrysochromulina is paraphyletic. C. polylepis, which produced a spectacular, harmful bloom in 1988, is more closely related to toxic Prymnesium species than to most other Chrysochromulina species based on rDNA sequence comparisons. Signatures were identified in the SSU rRNA gene specific for a clade that comprised primarily toxic taxa (C. polylepis, P. parvum, P. patelliferum and P. calathiferum) and that recognized C. polylepis alone. Oligonucleotide probes complementary to these regions were designed, and their specificity tested using dot-blot hybridization on PCR products of the SSU rRNA gene from 28 strains of Chrysochromulina and Prymnesium. Whole-cell hybridizations were performed with FLUOS- as well as Cy3-labelled probes on cultured species from both genera, and were detected with both epifluorescence microscopy and flow cytometry. The probes afforded easy identification of clonal isolates of C. polylepis and a cluster of closely related species including C. polylepis and Prymnesium spp. The feasibility of using these probes for species identification and studies of population dynamics in the field is discussed.

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.

Nucleotide gene sequences for both the nuclear-encoded small-subunit RNA (SSU) and plastid-encoded large subunit of RuBisCO (rbcL) were determined for 16 species classified in the red algal order Gelidiales. Sequence comparisons indicate that rbcL is evolving at a faster rate than SSU in these species and that there is a more even distribution of changes across the length of the rbcL gene compared with that observed for the SSU gene. The rbcL sequences also showed a marked anti-GC bias at synonymous third-codon base positions. Parsimony and maximum-likelihood analyses were used to generate phylogenetic trees from both separate and combined analyses of the two sequence data sets. Relationships among most taxa are resolved robustly; however, the relative order of branching for the Capreolia and Ptilophora clades remains uncertain. The molecular data provide unambiguous, independent support for recognition of the newly established genus Pterocladiella. Although the position of Pterocladiella within the Gelidiales was not resolved clearly by the rbcL data alone, analyses of both the SSU and combined data matrices indicate that this genus is one of the three earliest-diverging lineages within the order. These data also suggest that Gelidium as currently circumscribed is not monophyletic. Molecular and morphological evidence suggests that the origin and, perhaps, diversification of the major lineages of gelidialean algae is correlated with distinct, independently evolved nutritional strategies for the developing carposporophyte.

The temperature dependence of UV effects was studied for Arctic and temperate isolates of the red macrophytes Palmaria palmata, Coccotylus truncatus and Phycodrys rubens. The effects of daily repeated artificial ultraviolet B and A radiation (UVBR: 280–320 nm, UVAR: 320–400 nm) treatments were examined for all isolates at 6, 12 and 18 °C by measuring growth, optimal quantum yield of PSII (Fv/Fm) and cyclobutane–pyrimidine dimer (CPD) accumulation. Furthermore, possible ecotypic differences in UV sensitivity between Arctic and temperate isolates were evaluated. Large species-specific differences in UV sensitivity were observed for all parameters: the lower subtidal species C. truncatus and P. rubens were highly sensitive to the UV treatments, whereas P. palmata, which predominantly occurs in the upper subtidal zone, was not affected by these treatments. Only minor differences were found between Arctic and temperate isolates, suggesting that no differences in UV sensitivity have evolved in these species. Relative growth rates were temperature-dependent, whereas species-specific UV effects on growth rates were relatively independent of temperature. In contrast, the species-specific decrease in Fv/Fm and its subsequent recovery were temperature-dependent in all species. UV effects on Fv/Fm were lower at 12 and 18 °C compared with 6 °C. In addition, UV effects on Fv/Fm decreased in the course of the experiment at all temperatures, indicating acclimation to the UV treatments. CPDs accumulated during the experiment in both isolates of P. rubens, whereas CPD concentrations remained low for the other two species. CPD accumulation appeared to be independent of temperature. The results suggest that summer temperatures occurring in temperate regions facilitate repair of UV-induced damage and acclimation to UV radiation in these algae compared with Arctic temperatures. Because the differences in UV effects on Fv/Fm, growth and CPD accumulation were relatively small over a broad range of temperatures, it was concluded that the influence of temperature on UV effects is small in these species.

Plasmodesmata in photosynthetic eukaryotes are found in all embryophytes, in many members of the Chlorophyta, and in the Phaeophyceae. The Phaeophyceae and the Chlorophyta clearly developed cell walls and multicellularity independently, so that (in the absence of lateral gene transfer) plasmodesmata evolved independently in these groups. The minimum number of independent origins of plasmodesmata in the Chlorophyta based on molecular phylogenies is two (Chlorophyceae sensu lato, Charophyceae sensu lato). Other intercellular connections in members of the Chlorophyta (Ctenocladus, Smithsoniella, Volvox) are structurally very different from true plasmodesmata. Recently published taxonomies of the Chlorophyta have five classes (Chlorophyceae, Oedegoniophyceae, Trentepohliophyceae, Klebsormidiophyceae and Charophyceae sensu stricto) with plasmodesmata out of a total of thirteen. However, it is by no means clear that these classes all acquired plasmodesmata independently.

A continuous culture experiment was conducted with the marine diatom Ditylum brightwellii to assess the photo-oxidative effects of transition from dim light to high light at three successive levels. The focus was on temporary stress by ambient UVA at the water surface, via a simulation of the periodic ascent of diatoms caused by vertical mixing. Within a 14 h dim-light period, cells were exposed daily to 4 h of: (A) moderate PAR (100 μmol photon m-2 s-1), (B) high PAR (400 μmol photon m-2 s-1) and (C) high PAR (400–700 nm) plus 6·7 μmol photon m-2 s-1 (2·2 W m-2) UVA. Cell shape, life cycle and sinking rates were not affected by high PAR per se (mode B). The daily 4 h high-irradiance mode C, with additional UVA (UVA: PAR = 0·016), caused an increase in cell diameter, a decrease in length axes, and a production of vegetative resting stages. Superoxide dismutase (SOD) activities, oxidized glutathione (GSSG) pools and malondialdehyde (MDA) contents increased as well, which indicates that this biologically effective UVA dose (0·78 W m-2) promoted active oxygen production, oxidative stress and lipid peroxidation. Sinking rates in UVA-exposed D. brightwellii were higher than in those grown without UVA. A close correlation between sinking rates and MDA contents suggests that UVA-induced lipid peroxidation has altered the membrane functions which regulate buoyancy in D. brightwellii. Although UVA-induced formation of resting cells will contribute to accelerated sinking, it is not evident that this can be considered as a stress avoidance mechanism under adverse light (UVA) conditions. D. brightwellii proved to be sensitive to transitions from shade to natural surface irradiance conditions. In coastal waters, such large diatom species may experience oxidative stress after a few hours' residence near the water surface at ambient UVA levels.

Nostoc caeruleum, N. commune, N. microscopicum, N. parmelioides, N. pruniforme, N. verrucosum and N. zetterstedtii are all cyanobacteria forming macroscopically visible colonies. They were selected for a nature conservation case study. Their specific identity is easily determined, and reliable historical records are available. Life conditions for these species in Europe in the ‘virgin’ postglacial biosphere, historical reports and the present-day situation are surveyed. Data concerning type materials, supplements to the protologues, and morphology are presented. The classic descriptions and diagnoses based only on herbarium material are supplemented by ontogenetic details. Global/regional changes in the biosphere (climate, regulation of lake levels and river flows, import of plant nutrients, water pollution, acidification, etc.) and their consequences for aquatic biocoenoses are reviewed. The analysis of man-made impacts on the environment enables us to evaluate the present state of habitats where these algae occur today or where they are now extinct. Documented changes in environmental conditions in the past serve as a basis for assessing the likely future developments of the biotopes and of the whole landscape where these cyanobacteria form part of the biocoenoses. However, there are few recent detailed ecological studies on benthic and terrestrial cyanobacteria. It is not yet clear which of the different components covered by the comprehensive term ‘eutrophication’ is the decisive factor for the changes in aquatic biocoenoses and the decline of cyanobacterial biodiversity.