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.

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

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.

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

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

Cryptomonas sp. Φ is an undescribed cryptomonad used for many studies into the endosymbiotic origin of plastids. Cryptomonas sp. Φ was characterized using electron microscopy, DNA sequencing and karyotyping. DNA sequence data show that Cryptomonas sp. Φ has been confused with the related cryptomonad, Guillardia theta, which is the organism actually used in most published studies on cryptomonad endosymbiosis to date. It is proposed that the strain Cryptomonas sp. Φ be recognized as a distinct species under the name Hanusia phi. Although Hanusia phi shares molecular and karyotypic features with G. theta, it cannot be assigned to Guillardia because it does not fit the morphological description of this genus. H. phi differs from G. theta in periplast structure, configuration of the furrow-gullet system, and cell size. Morphologically, however, H. phi is very similar to Teleaulax acuta, Teleaulax merimbula and the diplomorph of Proteomonas sulcata.

The elemental composition of Ceratium hirundinella was determined in mixed phytoplankton samples collected over a 2-month period (late June to early September 1995). Electron probe X-ray microanalysis spectra of single cells routinely showed clear peaks of monovalent (Na, K) and divalent (Mg, Ca) cations, plus Si, P, S and Cl. Considerable variation in elemental concentrations occurred both within and between samples (20 cells). The overall ratio of monovalent to divalent cations was relatively constant at about 1.3. Intracellular concentrations of anions/cations and electronegative/electropositive elements were significantly correlated in most samples, suggesting a controlled internal balance of these ionic groups. Correlation analysis of elemental concentrations revealed clear patterns of statistical association within individual samples, with significant positive correlations between particular pairs of elements (Mg–P, K–Cl and K–P). Some pairs of highly correlated elements (particularly Mg–P) occurred in defined ratios throughout the samples, while others (e.g. K–Cl, Na–Mg) were variable. Factor analysis showed that elemental associations were determined by two Principal Factors in most samples, possibly related to insoluble and soluble components of cells. Decrease in the level of available P in lake water was associated with a sharp decrease in the intracellular P concentration and the concentration of other correlated elements. The estimated C/P ratio markedly differed from the classical (Redfield) value at times of low P availability. The concentration of P in cells of Ceratium was approximately 104 times greater than in the surrounding water medium (total P) compared with values of 102–103 for K.

The requirements for efficient utilization of high light fluxes in cultures of Spirulina platensis have previously been elucidated. The most important of these was a short light-path coupled with a highly turbulent flow, facilitating ultrahigh cell densities (i.e. above 100 mg chl l−1). The present study shows that for each irradiance there is an optimal culture density, defined as the concentration that yields the highest output rate of cell mass under the prevailing conditions. In ultrahigh cell density cultures, a linear relationship was observed between the output rate and the irradiance, up to a photon flux density (PFD) of 2500 μmol m−2 s−1. Using a total PFD of 8000 μmol m−2 s−1, a maximal output rate of 16.8 g dry weight m−2 s−1 was obtained, which is the highest reported for a culture of photoautotrophic microorganisms exposed to direct beam radiation. Testing the effect of reduction in light-path on productivity, output rate per unit volume increased 50-fold as the light-path was reduced 27-fold, i.e. from 200 mm to 7.5 mm. Likewise, the output rate calculated on an areal basis was almost doubled, increasing from 2.5 to 4.6 g m−2 s−1, and the specific growth rate increased c. 20% as the light-path was reduced to 7.5 mm. The very significant effect of the length of the light-path on enhancing the output rate is interpreted as resulting from improvement in the light regime to which the individual cells are exposed, as reflected in the frequency and overall characteristics of the light–dark cycles.

Changes in relative abundance of estuarine epipelic microalgae along an estuarine gradient were investigated, and population densities of different species along a small-scale nutrient gradient generated by a sewage treatment outfall and in laboratory mesocosms enriched with ammonium were also studied. The relative abundance of certain species of epipelic diatoms was related to location along the estuarine salinity and nutrient gradient: Navicula gregaria and N. phyllepta were abundant at oligo- and mesohaline sites respectively, and Pleurosigma angulatum and Plagiotropis vitrea were abundant at polyhaline sites. On a smaller spatial scale, though there were no significant patterns in microalgal biomass in relation to nutrient enrichment, there were significant differences in the population densities of different epipelic species along a multivariate nutrient gradient (decreasing concentrations of ammonium, nitrite, silicate, organic content, and increasing salinity and pore-water nitrate concentrations) away from a sewage outfall along a saltmarsh creek. The diatoms Nitzschia sigma and Gyrosigma limosum and the cyanobacteria Oscillatoria limosa and O. princeps had significantly higher population densities near the outfall, and Navicula phyllepta, N. pargemina, Nitzschia frustulum, Cylindrotheca signata and Pleurosigma angulatum were significantly more abundant at the seaward end of the gradient. In laboratory tidal mesocosms, sediment cores from along the gradient had their pore-water ammonium concentrations increased to 380–450 μM NH4+. After 26 days, the population densities of Gyrosigma fasciola, G. littorale, P. angulatum, N. phyllepta, Cylindrotheca signata, C. closterium and Niztschia apiculata were significantly reduced, while those of G. limosum, N. sigma, Scolioneis tumida and O. limosa were unaffected, or were significantly higher compared with control cores. Laboratory manipulations of ammonium concentrations supported the observed field distributions, indicating that epipelic species do have different trophic preferences and ammonium concentration may be a significant factor in determining estuarine species composition of epipelic algae.