The taxonomic status of three closely related species of the brown algal genus Elachista, E. tenuis Yamada, E. sargassicola Noda and E. nipponica Umezaki (Elachistaceae, Ectocarpales sensu lato) was reassessed on the basis of morphological observations including laboratory culture experiments and molecular phylogenetic analyses. These species share characteristic assimilatory filaments of constant width throughout their length except for slightly constricted bases and slightly tapering apices. Although E. sargassicola has been characterized by the presence of phaeophycean hairs, our culture experiments revealed that the presence or absence of such hairs is not a stable taxonomic feature in E. tenuis and E. sargassicola. Furthermore, molecular analyses showed that the rRNA ITS1 and ITS2 regions of E. tenuis and E. sargassicola were nearly identical and grouped them in a strongly supported monophyletic clade. Thus, E. sargassicola should be reduced to synonymy with E. tenuis. On the other hand, E. nipponica, which has been characterized by the production of cylindrical cells in a basal hemispherical cushion, formed cylindrical cells under experimental culture conditions, indicating that the production of such cells is a specific feature of E. nipponica. However, another reported feature of E. nipponica, the production of intercalary plurizoidangia in assimilatory filaments, was rejected, because reexamination of type material revealed that filaments bearing such reproductive structures are referable to Leptonematella fasciculata (Reinke) Silva. Molecular phylogenetic analyses support the distinction of E. tenuis and E. nipponica.

The taxonomy of Vitreochlamys species (Volvocales, Chlorophyta) was studied with light and electron microscopy; DNA sequence data were obtained for nine strains from various localities in Japan, the Czech Republic, Slovak Republic and Germany. The strains could be delineated clearly into six species – V. fluviatilis (Stein) Batko, V. gloeocystiformis (Dill) Nakazawa, comb. nov., V. ordinata (Skuja) Nakazawa, comb. nov., V. nekrassovii (Korshikov) Nakazawa, comb. nov., V. aulata (Pascher) Batko, and V. pinguis Nakazawa, sp. nov. – on the basis of differences in cell and protoplast shape, numbers of contractile vacuoles and pyrenoids, form and position of the stigma, location of the nucleus, degree of longitudinal striations on the chloroplast surface, and ultrastructure of the pyrenoid and stigma. Although V. pinguis and V. aulata share common chloroplast morphology, including stigma and pyrenoid ultrastructure, these two species can be distinguished clearly by cell shape, the number of contractile vacuoles and location of the nucleus. In addition, phylogenetic sequence data of the rbcL (large subunit of Rubisco, ribulose-1,5-bisphosphate carboxylase/oxygenase) gene from all of the Vitreochlamys strains strongly suggest that V. pinguis from Japan is robustly separated from the clade composed of four strains of V. aulata from the Czech Republic, Slovak Republic and Japan. The sequence data also showed that Vitreochlamys is composed of three clades, which are largely consistent with the ultrastructural features of the stigma and pyrenoids.

A new benthic marine dinoflagellate, Bysmatrum granulosum Ten-Hage, Turquet, Quod & Couté, sp. nov., was obtained from sediment and coral samples from sites of La Réunion Island (SW Indian Ocean). This new species is described and illustrated by light and scanning electron micrographs. Cells are 40–50 μm long and 40–46 μm wide. The epitheca is conical and smaller than the hypotheca, which is trapezoidal with convex sides. Plate tabulation is typical for the genus (P0, X, 4′, 3a, 7′′, 6c, 5s, 5′′′, 2′′′′); epithecal plates 3′ and 4′′ separate the intercalary plates 2a and 3a. Thecal plates are perforated by pores and covered by both small and minute wart-like projections, linearly arranged, radiating from the apical pore. This new species differs from the three others of the genus Bysmatrum in the following characters: cell shape and size, size of the apical pore complex and features of thecal plates (plate shapes and ornamentations).

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.

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.

Experiments were conducted during October 1998 in Lake Titicaca, Bolivia (16° S, 68° W, 3810 m a.s.l), to determine the effects of solar ultraviolet radiation (UVR) on phytoplankton photosynthetic rates and DNA damage. Water samples were taken daily and incubated in situ or in simulated in situ conditions using sharp cut-off filters to eliminate various portions of the UVR spectrum. The total inhibition of photosynthesis due to UVR in surface waters was 85%; the greatest part of this inhibition (65%) was due to UVAR (315–400 nm), the rest (20%) being due to UVBR (280–315 nm). The inhibition of photosynthesis decreased with depth so that there were no significant differences among treatments at 1·3 optical depths (KPAR). The loss of carbon assimilation in the integrated production over the euphotic zone (4·6 optical depths) was 17·4%, with 14% due to UVAR and an additional 3·4% due to UVBR. Lake Titicaca phytoplankton had a threshold for inhibition of photosynthesis at about 0·3 W m−2 for UVBR and 5 W m−2 for UVAR, below which no inhibition was detected. Above this threshold, photosynthetic inhibition increased steadily, with UVAR having the greatest effect. Analysis of biological weighting functions (BWFs) indicated that phytoplankton from Lake Titicaca was less sensitive to UVR than phytoplankton from other regions. DNA damage (evaluated through the formation of cyclobutane pyrimidine dimers, CPDs) was observed for a simulated worst-case situation (i.e. samples incubated in full sunlight) and significant CPD accumulation was found as a result of UVBR exposure, but not with UVAR. However, absolute levels of damage were relatively low when compared with results obtained at other locations, also suggesting the low sensitivity of Lake Titicaca phytoplankton to UVR. It seems that UVBR stress in these organisms acts via at least two cellular targets: the photosynthetic apparatus and nuclear DNA. Our results suggest that an eventual enhancement of UVBR, due to ozone depletion, would have little impact on the phytoplankton of Lake Titicaca.

Different stages of the automortality in phytoplankton have been studied applying flow cytometry. These stages are, in order of expression: (1) compromised cell membranes, (2) degradation of the photosynthetic pigments and reduction of the photosynthetic activity, (3) fragmentation of the genomic DNA. The integrity test of the cell membranes is based on the inability of the DNA-specific stain SYTOX Green to pass into cells with intact plasma membranes. The reduction in photosynthetic activity was examined by sorting 14C-labelled phytoplankton cells differing in viability. Finally, DNA fragmentation was traced by measuring changes in genomic DNA. The different phytoplankton species tested showed a great variety in response when grown under the same conditions, but there was also considerable intraspecific variation. Unstained cells, fully stained cells (equivalent to full staining of genomic DNA in fixed cells) and cells with intermediate fluorescence signal occurred together within the same culture. The photosynthetic activity in cells with a reduced viability dropped by as much as 60% relative to that of the viable cells. In the subsequent stage, when photosynthetic pigments were fully degraded, this value dropped further to around 10%. Cells in this stage also showed subdiploidy as a result of genome fragmentation. Field tests using samples of phytoplankton collected in the North Atlantic Ocean (40° N, 23° W) during spring showed staining properties similar to those found in cultures grown at suboptimal growth conditions. The percentage of non-viable cells varied considerably (ranging from 5% to 60%) between the various phytoplankton groups present. The lowest value was observed for Synechococcus, but some pico-eukaryotes showed percentages as high as 60%. Moreover, the viability varied with depth (light level) and over a light–dark cycle. The present findings suggest the existence of a (genetically based) uniform process of automortality in phytoplankton. Non-viable cells are a substantial component of the oceanic phytoplankton, affecting the food-web structure and species succession.

Modern chemical residues from water pollution (such as herbicides, antibiotics and even chemical substances of military use) are a challenge to survival of microalgal populations. Adaptation of three microalgal species – Pseudanabaena planctonica (Cyanophyceae), Dunaliella tertiolecta (Polyblepharidaceae, Chlorophyceae) and Scenedesmus sp. (Chlorophyceae) – to growth and survival in the presence of erythromycin, 3-(3,4-dichlorophenyl)-1,1-dimethylurea, and 2,4,6-trinitrotoluene was analysed as an experimental model. Growth of these species was restricted even by micromolar concentrations of such xenobiotics. When such contaminants are added to a dense microalgal culture, the cell density will be reduced after a few days due to the death of sensitive cells. However, after further incubation for several days, the culture will sometimes increase in density again due to the growth of a cell variant which is resistant to the contaminants. A Luria–Delbrück fluctuation analysis was carried out to distinguish between resistant cells arising from rare spontaneous mutation and resistant cells arising from other mechanisms of adaptation. In all cases, the contaminant-resistant cells arise randomly by rare spontaneous mutation during replication of cells prior to the addition of the contaminant (pre-selective mutations). Since wild-type microalgal genotypes are unable to survive in the presence of such contaminants, spontaneous pre-selective mutation (i.e. mutation from herbicide sensitivity to herbicide resistance) offers insights into the evolutionary capabilities of microalgal populations in contaminated environments. The rate of spontaneous mutation from sensitivity to resistance ranged from 2·0×10−6 mutants per cell division for erythromycin sensitive [xrarr ] erythromycinresistantP. planctonica to 8·2×10−6 mutants per cell division for TNTsensitive [xrarr ] TNTresistantScenedesmus sp. Since contaminant-resistant mutants have a diminished fitness, the resistant variants are maintained in the absence of the contaminants as the result of balance between new resistant cells arising from spontaneous mutation and resistant cells eliminated by natural selection. Thus recurrence of rare spontaneous pre-selective mutations ensures the survival of microalgal population in suddenly polluted environments.

In a recently published examination of the newly re-discovered holotype of Leptophytum (Lithophyllum) laeve, the characters of the holotype specimen were judged to be taxonomically inadequate. Consequently, an epitype was selected which was determined to belong to Phymatolithon lenormandii, rendering Leptophytum and its type L. laeve junior synonyms of Phymatolithon and P. lenormandii, respectively. We have re-studied the holotype specimen in Stockholm, and in this paper we demonstrate that it is consistent with the protologue and exhibits features that are fully consistent with the modern circumscription of Leptophytum laeve, based on population studies. Our results demonstrate that the holotype specimen is taxonomically adequate and that the selection of an epitype was not necessary. Accordingly, we propose the re-instatement of Leptophytum Adey 1966, based on its type L. laeve (Foslie) Adey (basionym: Lithophyllum lenormandii f. laeve Foslie 1891). The genera Leptophytum and Phymatolithon Foslie are similar in some anatomical respects (such as in having diminutive sub-epithallial initials, i.e. meristem cells, a polystromatic non-coaxial hypothallium, and roundish to flattened epithallial cells in transverse section). The genera differ somewhat in morphology and markedly in most reproductive features (such as spermatangial systems, origin of gonimoblasts, position of conceptacle primordia, and the presence or absence of distinct asexual conceptacle pore cells). The taxonomic, ecological and biogeographic characteristics of the two genera lead us to conclude that the similarities between Phymatolithon and Leptophytum have very likely resulted from parallel evolution.