This work attempts to identify growth conditions for maximal productivity of cell mass and of eicosapentaenoic acid (EPA) in ultrahigh cell density cultures of Nannochloropsis sp. Using flat plate reactors with a narrow (1–2 cm) light path and rigorous stirring exposed to high photon flux densities (1000–3000 μmol photons m−2 s−1), record population densities (1·2–1·4×1010 cells ml−1) were obtained. Consequently, the EPA content of the culture (mg l−1) was higher by some two orders of magnitude than reported hitherto for cultures of much lower cell concentrations. In continuous cultures, highest culture EPA yield coincided with maximal output rate of cell mass. The very high population densities and output rates of cell mass and of culture EPA were possible provided culture medium was replaced at least every 48 h. Inhibitory activity, for which a bioassay was developed, was thereby removed. When nutrients were added frequently in order to prevent nutrient limitation without removing the inhibitory activity in the cultures, cell proliferation ceased after reaching some 30% of the attainable maximal cell number, and the culture gradually deteriorated. Inhibitor-induced culture deterioration was fully reversible when the growth medium was replaced with fresh medium.

How are microphytobenthic biofilms adapted to the high incident irradiances and temperatures, low inorganic nutrient concentrations and high desiccation stresses on intertidal flats present in tropical environments? This study investigated biofilms subject to different environmental conditions in a range of tropical sites in Suva lagoon, Fiji. PAM fluorescence was used to measure photophysiological responses to the light climate. Biofilm colloidal carbohydrate, extracellular polymeric substances (EPS) and low molecular weight (MW) carbohydrate concentrations and diel carbohydrate production patterns were measured. Average biomass (Chl a) ranged from 15 to 36 mg m−2, and was highest in seagrass bed sediments, but biomass was not correlated with water column or sediment porewater nutrient concentrations. Biofilm photophysiology differed significantly along a combined gradient of light and nutrient availability, with Fv/Fm, relative ETRmax and Ek of biofilms highest in mangrove and intertidal main island sites and lowest in subtidal coral reef flats. Subtidal biofilms showed photoinhibition at irradiances >1000 μmol m−2 s−1. Significant correlations between Chl a and colloidal carbohydrate concentrations were present (except on intertidal sandflats), and tropical biofilms had higher ratios of colloidal carbohydrate and EPS to Chl a than temperate estuarine biofilms, probably due to a combination of high irradiance and low nutrient availability leading to the production of excess photoassimilates. The percentage of EPS present in the colloidal fraction was highest in coral sand biofilms (42%), which had the lowest nutrient concentrations, compared with other sites (25–32%). Intertidal biofilms predominantly consisted of large motile taxa and showed strong rhythms of vertical migration. During tidal emersion, high sediment temperatures (41 °C), irradiance (>2300 μmol m−2 s−1) and salinity (49‰) stimulated downward migration. In silty sediments, migration resulted in a reduction in photosynthetic activity during the midday period but, in sands with high light penetration (to a depth of >1700 μm), high production rates of EPS (18.2 μg carbo. μg Chl a−1 h−1) and low MW carbohydrate exudates (40.2 μg carbo. μg Chl a−1 h−1) occurred. Vertical migration, high Ek and high rates of photoassimilate dumping are all adaptations to living in the tropical intertidal zone. Seagrass and reef flat biofilms consisted of a diverse non-migratory flora of motile and non-motile taxa that were not subject to such extreme temperature and irradiance conditions. Low values of photosynthetic parameters and high colloidal and EPS content indicated that these biofilms were nutrient-limited.

Fourier-transform infrared (FTIR) spectroscopy was carried out on single colonies of Pediastrum duplex present in air-dried preparations of mixed phytoplankton samples isolated from a eutrophic freshwater lake. FTIR absorption spectra had 12 distinct bands over the wavenumber range 3300–900 cm−1 which were tentatively assigned to a range of chemical groups, including -OH (residual water, wavenumber 3299 cm−1), -CH2 (lipid, 2924), -C=O (cellulose, 1739), amide (protein, 1650 and 1542), >P=O (nucleic acid, 1077) and -C-O (starch, 1151 and 1077). Measurement of band areas identified residual water, protein and starch as the major detectable constituents. Areas of single bands and combined bands of -CH2, -C-O and >P=O species normalized to protein (to correct for differences in specimen hydration and thickness) showed wide variation between colonies, indicating environmental heterogeneity. Correlation analysis demonstrated close statistical associations between different molecular species. Particularly high levels of correlation between bands 3/4 (CH2), 6/7 (amide) and 8/9 (-CH3) was consistent with their joint origin from the same molecular species. The isolation of bands 11 and 12 in the correlation pattern was confirmed by factor analysis, suggesting that variation in the level of starch is statistically unrelated to other macromolecules being monitored. The use of FTIR spectroscopy to characterize an algal micro-population within mixed phytoplankton has potential for future studies on biodiversity and environmental interactions at the species level.

The dependence of the cellular (biogenic) and frustule-associated (mineralized) silica content of the diatoms Navicula salinarum and Thalassiosira weissflogii on salinity and aluminium conditions was studied in order to make it possible to manipulate silicification in vitro and maximize it to levels required for physico-chemical frustule characterization by physisorption, X-ray scattering analysis and NMR, which is our ultimate objective. Enrichments with AlCl3 increased growth and the final cell density of the pennate N. salinarum, but not of the centric species T. weissflogii. Aluminium additions did not, however, result in a significant increase in the biogenic or mineralized silica content per cell and could not be detected in the silica matrix of the frustule. In contrast, lowering the salinity from 28 practical salinity units (PSU) to 20 and 15 resulted in a significant increase in the biogenic silica content per cell of both species, which is in line with an increase in density of the chemically derived silica under low salt conditions. The silica content per cell was variable during culture growth; increase in cell densities (during exponential growth) was accompanied by a decrease in contents of biogenic silica per cell. Electron microscopy and energy dispersive X-ray analysis (EDXA) support the chemical analyses and also suggest higher biogenic silica contents at lower salinities. The results indicate that besides silicate concentration and pH, the concentration of salts is an important inorganic factor that affects the silica polymerization inside the silica deposition vesicle of diatoms.

Phylogenetic analyses, based upon nuclear small-subunit ribosomal RNA gene sequences, of four ‘chlorosarcinoid’ species referred to Planophila Gerneck show that the genus is polyphyletic. The type species, P. laetevirens Gerneck, is closely related to species in the Ulotrichales, Ulvophyceae. The monotypic sarcinoid genus Pseudendocloniopsis is the closest relative of Planophila; the two genera represent the addition of a new morphological type to the Ulotrichales. Planophila microcystis (Dangeard) Kornmann & Sahling forms a clade at the base of the Ulvophyceae with Oltmannsiellopsis, and thus belongs to the Oltmannsiellopsidales. This result is also supported by the Oltmannsiellopsis-like ultrastructure of P. microcystis zoospores. Planophila sp. B from Antarctica, which has Trebouxia-like pyrenoid structure, is a trebouxiophyte closely related to Chlorella-like unicellular coccoids, Stichococcus bacillaris and Prasiola species. This is the first robustly supported molecular phylogenetic analysis that places Prasiola in the Trebouxiophyceae. As shown previously, P. terrestris Groover & Hofstetter belongs to the Chaetopeltidales, Chlorophyceae. Dangemannia gen. nov. (type species: D. microcystis (Dangeard) comb. nov.), Floydiella gen. nov. (type species: F. terrestris (Groover & Hofstetter) comb. nov.) and Pabia gen. nov. (type: P. signiensis sp. nov.) are proposed.

Autotrophic picoplankton (APP) abundance, primary production and vertical distribution were studied in the oligotrophic Lake Stechlin (northeastern Germany) in 1994 and 1995. Within the euphotic zone APP contributed 34% of phytoplankton biomass and 35% of primary production. Annual average APP cell number was 209×103 cells ml−1, of which 95% were unicellular cyanobacteria, 2% were colonial cyanobacteria and 3% were eukaryotes. Three ecologically and/or morphologically different groups of APP were recognized: (i) unicellular cyanobacteria belonging to the genus Cyanobium, (ii) eukaryotic species growing in early spring under isothermal conditions and (iii) cyanobacteria, partly colonial species, growing in the stratified period in the euphotic zone. Three species of eukaryotic green algae were identified: Choricystis minor, Neocystis diplococca and Pseudodictyosphaerium jurisii, the latter two being colonial. This is the first record of the occurrence of colonial eukaryotes potentially of APP size in fresh waters. In summer picocyanobacteria were highly productive so the low net increase rates indicate that losses must be high. The dominant, Cyanobium population started growing in February with maximum abundance in late April, contributing significantly to the spring peak in phytoplankton biomass. During this growth period, the population was evenly distributed in the 60 m water column. By the time the maximum biomass occurred, inorganic nutrients had decreased below analytically detectable levels. Parallel to the onset of stratification a part of the population was grazed, most probably in the microbial loop and primarily in the upper 10–15 m. The rest of the Cyanobium population accumulated in a narrow layer in the upper hypoliminon. The APP remaining from the spring was persistent for much of the summer in this cold, high-nutrient (especially nitrate)/low-light environment. Short phosphorus-turnover times suggest that APP is probably phosphate-limited. The stability of the thermocline and the pattern of thermocline development in May affected the accumulation of the APP cells in the upper hypolimnion. Thus, this process is sensitive to the physical stability of the water column.

Growth parameters of Mesophyllum alternans and Lithophyllum frondosum were studied in the northwestern Mediterranean. Growth and shrinkage rates, in terms of area gained or lost per month, were measured for both crustose corallines over a 2 year period by photographic and computer-assisted image analysis. No seasonal pattern in growth or shrinkage was found for either species. M. alternans grew and shrank at significantly higher rates than L. frondosum. Growth rates for both species were over an order of magnitude lower than those previously reported for other Mediterranean and tropical species, and were similar to reports for crustose corallines in Arctic and temperate waters. Almost 50% of monitored M. alternans thalli underwent at least one fission or fusion event over the 2 year monitoring period, while in L. frondosum these events were rarely observed. Interspecific differences in rates of growth, shrinkage, fission and fusion appear to depend on differences in thallus thickness (M. alternans is thin and L. frondosum is thick). These differences were interpreted as distinct biological strategies of persistence and the occupation of primary substratum.

Enteromorpha intestinalis grows along the Swedish west coast in rockpools which are isolated from the open seawater for long time periods and where, therefore, the inorganic carbon content is low and the pH is high during the day. In order to investigate how E. intestinalis could grow under such apparently CO2-constraining conditions, we measured its photosynthetic responses to inorganic carbon in the presence of an inhibitor of external/surface-bound carbonic anhydrase (acetazolamide) as well as an inhibitor of HCO−3 transport via anion exchange (4,4′-diisothiocyanatostilbene-2,2′-disulfonate). The results show that both HCO−3 dehydration via surface-bound carbonic anhydrase and HCO−3 transport via a 4,4′-diisothiocyanatostilbene-2,2′-disulfonate-sensitive mechanism were present in E. intestinalis, but only HCO−3 uptake via the putative transporter was operative in rockpool water during most of the photic period (pH > 9·4, inorganic carbon < 0·45 mol m−3 and CO2 < 0·05 mmol m−3). The advantage of such a mechanism, rather than extracellular HCO−3 dehydration, is discussed with regard to photosynthesis of marine macroalgae under in situ conditions conducive to high pH values adjacent to the thalli.

Sequence variation among 22 isolates representing a global distribution of the prymnesiophyte genus Phaeocystis has been compared using nuclear-encoded 18S rRNA genes and two non-coding regions: the ribosomal DNA internal transcribed spacer 1 (ITS1) separating the 18S rRNA and 5·8S rRNA genes and the plastid ribulose-1,5-bisphosphate carboxylase/oxygenase (RUBISCO) spacer flanked by short stretches of the adjacent large and small subunits (rbcL and rbcS). 18S rRNA can only resolve major species complexes. The analysis suggests that an undescribed unicellular Phaeocystis sp. (isolate PLY 559) is a sister taxon to the Mediterranean unicellular Phaeocystis jahnii; this clade branched prior to the divergence of all other Phaeocystis species, including the colonial ones. Little divergence was seen among the multiple isolates sequenced from each colonial species complex. RUBISCO spacer regions are even more highly conserved among closely related colonial Phaeocystis species and are identical in Phaeocystis antarctica, Phaeocystis pouchetii and two warm-temperate strains of Phaeocystis globosa, with a single base substitution in two cold-temperate strains of P. globosa. The RUBISCO spacer sequences from two predominantly unicellular Phaeocystis isolates from the Mediterranean Sea and PLY 559 were clearly different from other Phaeocystis strains. In contrast, ITS1 exhibited substantial inter- and intraspecific sequence divergence and showed more resolution among the taxa. Distinctly different copies of the ITS1 region were found in P. globosa, even among cloned DNA from a single strain, suggesting that it is a species complex and making this region unsuitable for phylogenetic analysis in this species. However, among nine P. antarctica strains, four ITS1 haplotypes could be separated. Using the branching order in the ITS1 tree we have attempted to trace the biogeographic history of the dispersal of strains in Antarctic coastal waters.

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.

Patterns of nuclear and organelle inheritance among artificial hybrids of the seaweeds Fucus serratus and F. evanescens were detected using single-strand conformation polymorphism (SSCP). Three alleles were identified in the 231 bp rDNA-ITS1 gene (nuclear): two in F. serratus and one in F. evanescens. Alleles differed by 1–2 bp and all hybrids possessed one allele from each parent. Two haplotypes were present in the 288 bp Rubisco spacer (chloroplast), differentiated by a 33 bp indel. Two haplotypes differing by a single nucleotide were found in a 135 bp region of nad11 gene (mitochondrion). Both organelles are maternally inherited, as all hybrids contained the haplotypes of the parent contributing the egg. Although laboratory hybrids among Fucus spp. have been produced previously, this is the first time that both nuclear and cytoplasmic genetic markers have been used to document inheritance patterns. SSCPs analysed on an automated sequencer offer a rapid and powerful approach for identifying suspected hybrids from field samples, as well as a screen for intraspecific and intra-individual variation in DNA regions prior to confirmation of variations by sequencing.

Cryopreserved Chlamydomonas reinhardtii cultures remained viable when frozen by cooling slowly to −55°C, then plunging into liquid nitrogen for at least 1 day of storage. High viability (>40%) was retained when cultures contained 2–10% (v/v) methanol as a cryoprotective agent prior to freezing, while dimethyl sulphoxide was ineffective. However, methanol was lethal to cells in the presence of light. Frozen cultures became non-viable within 24 h when stored at −80°C, whereas those stored below −130°C remained viable for at least several months. Highest viability was attained in cultures that were frozen and stored at a low cell density. High viability also required that frozen cultures be warmed rapidly and the cryoprotective agent removed immediately thereafter in preparation for culturing in liquid or on solid medium. Individual cell viability was determined by measurements of colony counts after cell plating and by the penetration of Evans blue dye into non-viable cells. Viability in bulk culture was conveniently measured by comparing the rates of photosynthetic oxygen evolution, corrected for dark respiration, in previously frozen cultures with the corresponding rates in unfrozen controls. Cultures that had lost viability as measured by a decline in whole-cell photosynthetic oxygen evolution after freezing and thawing retained functional Photosystem II activity for some time thereafter, indicating that the loss in photosynthetic activity was due to some process other than photoinhibition of Photosystem II.

Molecular and breeding studies on two pan-tropical marine red algae reveal vastly different levels of genetic variation and reproductive isolation. Sequenced DNA regions from the nuclear, mitochondrial and plastid genomes (partial LSU rRNA, cox2-3 spacer, RuBisCo spacer, respectively) revealed high genetic variation among individuals of Spyridia filamentosa. An rbcL analysis shows that Spyridia is a monophyletic genus distinct from other Ceramiaceae sampled, suggesting that the Ceramiaceae could be paraphyletic. There is complete congruence between all data sets of S. filamentosa, showing a well-supported phylogeographic pattern with samples from the Pacific distinct from Atlantic and Indian Ocean samples. One western Mediterranean sample is associated with Atlantic specimens, while an eastern Mediterranean sample has closer affinities to Pacific samples, possibly indicating a recent cryptic introduction into the eastern Mediterranean. Limited breeding studies imply that these samples are mostly reproductively isolated, whereas a successful cross demonstrated maternal inheritance of organellar DNA. These data indicate that S. filamentosa exists as several cryptic species. Murrayella periclados exhibits low levels of genetic variation and no phylogeographic structure, and almost complete reproductive compatibility between isolates. This suggests that all M. periclados samples share a recent common ancestor that may have dispersed relatively rapidly, or that rates of base pair substitution between these two species vary greatly. Rapid long-distance dispersal of M. periclados is not indicated by what is known of the biology of M. periclados, especially in comparison with S. filamentosa, which appears to be a much better candidate for long-distance dispersal. These data demonstrate that red algal morphospecies are not equivalent units of diversity, with implications for our view of red algal biodiversity and evolution.

Repair of DNA damage induced by ultraviolet-B radiation (UVBR) was investigated in the sublittoral red alga Rhodymenia pseudopalmata at different temperatures, using immunofluorescent detection of thymine dimers. Photoreactivation of thymine dimers was completed within about 3 h at 6, 12 and 18 °C in the presence of ultraviolet-A radiation (UVAR) and photosynthetically active radiation (PAR) but no repair was found in dark-incubated fragments after 16–17 h. In plants previously exposed to a low UVBR dose (biologically effective dose: BEDDNA300 = 1·6 kJ m−2; unweighted irradiance = 0·72 W m−2 for 4 h), photoreactivation started within the first hour under UVAR+PAR at 18 °C but repair only started after 1–2 h at 12 and 6 °C. At 6 °C, repair was more efficient after exposure to a high UVBR dose (BEDDNA300 = 3·9 kJ m−2; unweighted irradiance = 0·78 W m−2 for 5 h) than to a lower dose (BEDDNA300 = 1·6 kJ m−2); no such difference was found at 18 °C. It is concluded that R. pseudopalmata is able to repair DNA damage induced by high UVBR doses efficiently.

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.

Thermal acclimation following changes from 6 °C to 15 °C and from 15 °C to 25 °C was investigated in the diatom Chaetoceros calcitrans. Cell division rate increased with temperature. Cellular carbon showed a slight decrease with an increase in temperature from 6 °C to 15 °C but showed no further change with an increase to 25 °C. Cells grown at 6 °C had low levels of light-harvesting components and a high carotenoid to chlorophyll a (Chla) ratio due to an increase in abundance of photoprotective pigments. The abundance of light-harvesting pigments increased with temperature and this was mirrored by a decrease in carotenoid:Chla ratio. All pigments showed an immediate change in abundance following each temperature shift. However, changes in photoprotective pigments reached a plateau after 12 h, in contrast to the light-harvesting pigments that took 4 days to become acclimated. Light-saturated rates of photosynthesis were at a minimum at 6 °C and increased twofold with temperature between 6 °C and 25 °C. Light-limited photosynthesis showed little change with temperature. It is suggested that, at low temperatures, the rate of carbon fixation is impaired due to a decrease in the activity of photosynthetic enzymes. This imparts an increase in excitation pressure due to an imbalance between light absorption and utilization. Cells respond to this by decreasing their light-harvesting capacity and increasing their ability to dissipate the excess energy. This fairly rapid regulation may be ecologically advantageous in areas where there are transient temperature changes.

Two brown algae, Pelvetia canaliculata and Laminaria saccharina, from the higher and lower mediolittoral belts respectively, have been tested for their capacity to overcome high-light stress in water and in air (in both fully hydrated and desiccated states). When exposed to supersaturating light irradiance in water, the two species developed non-photochemical quenching of fluorescence (NPQ) which was correlated with an increase in the de-epoxidation ratio (DR) of the xanthophyll cycle carotenoids (violaxanthin, antheraxanthin and zeaxanthin) and was followed by a slower decrease in oxygen evolution. NPQ reached values of up to 9 in P. canaliculata but only 4·5 in L. saccharina, at DRs of 0·65 and 0·5, respectively. In air, the xanthophyll cycle was also operative but the efficiency of de-epoxidation decreased linearly with the degree of hydration of the thallus. Photoprotection capacities in air also appeared higher in P. canaliculata than in L. saccharina, probably due to the higher molar content of the xanthophyll cycle pool size relative to chlorophyll a (Chl a) in the former (nearly double of that L. saccharina at 19 carotenoid molecules per 100 Chl a), which may be associated with a higher DR at the same level of desiccation. The concomitant higher accumulation of zeaxanthin in P. canaliculata might divert a higher percentage of the incident energy from the reaction centres, as demonstrated by the levels of NPQ, with steady-state fluorescence reduced to below the initial F0 level. Such differences, together with the unequal resistance to desiccation of the operation of the xanthophyll cycle, should be considered as possible factors responsible for the distribution for these two species on the shore.

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.

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.

Systematics of the red algal order Acrochaetiales and related taxa was investigated using combined small- and large-subunit nuclear ribosomal DNA (SSU and LSU rDNA, respectively) sequence data. These data were subjected to distance, parsimony and maximum likelihood analyses. The resulting phylogenies were congruent with previously published SSU results in that all included orders (Balbianiales, Batrachospermales, Nemaliales, Palmariales and Thoreales) were resolved as monophyletic except the Acrochaetiales, which consisted of two lineages (Acrochaetiales I and II). The Batrachospermales and Thoreales occupied equivocal positions as early diverging lineages, while the Balbianiales generally resolved as sister to an Acrochaetiales–Nemaliales–Palmariales (ANP) complex. Relationships among the four lineages of the ANP complex were not completely resolved, but detailed analyses weakly positioned Acrochaetiales II as sister to the Nemaliales, whereas Acrochaetiales I displayed a moderate to strong affiliation with the Palmariales. Acrochaetiales I included representatives of the genera Acrochaetium,Audouinella and Rhodochorton, whereas Acrochaetiales II had a number of acrochaetioid species including a representative of the genus Colaconema. Compared with published SSU phylogenies, bootstrap values within the two Acrochaetiales lineages increased substantially in combined SSU/LSU analyses. Based on these results, emended generic descriptions are provided for Acrochaetium, Audouinella, Colaconema and Rhodochorton, and a new family of acrochaetioid algae is described, the Colaconemataceae J. T. Harper et G. W. Saunders. The Acrochaetiaceae now includes the genera Acrochaetium, Audouinella and Rhodochorton, while the Colaconemataceae is considered monogeneric at this time. It is quite likely that additional genera will be recognized within the Colaconemataceae pending further investigation. Acrochaetiaceae is retained as the sole family of the Acrochaetiales, although the tenuous recognition of the Palmariales as distinct from this order is discussed, whereas Colaconemataceae is transferred to the new order Colaconematales J. T. Harper et G. W. Saunders.