The sublittoral red alga Delesseria sanguinea was pre-cultivated in the laboratory in a predominantly green light field at 10 μmol m−2 s−1 (10 °C), with an approximately 0·5% daily increase in blade area. Such pre-cultivated blades were exposed horizontally in flow-through chambers for 5–6 days in April and May to solar radiation reduced to 19% and 11%, respectively, by neutral density screens. In all three experiments, the full solar spectrum (UVB+UVA+PAR) reduced growth rate significantly to 0–50% of values obtained in PAR alone, while this occurred with UVA+PAR in only one experiment. The growth rate of a Delesseria blade may thus be used as a sensitive and reliable biological indicator of UVB in natural solar radiation at a pre-chosen, neutral reduction level. Rapid measurements of growth rate of apical parts of Delesseria blades during and after UVB+UVA pulses of 2, 3 or 6 h duration were performed in the laboratory by measuring thallus area every 2 min by means of a CCD camera coupled to an on-line, computer-aided image analysis system. A single pulse of 2 or 3 h duration administered during the light phase caused a temporary drop in growth rate during and after the pulse, with recovery starting 2·5 h after the end of the pulse and completed by the end of the light phase. A single 6 h pulse at a biologically effective UVB dose (BEDDNA300 nm) of only 0·5 kJ m−2 reduced growth rate by 55% if administered around noon, but halted growth almost completely if supplied at night, when no photoreactivation was possible. The UVB-sensitive behaviour of Delesseria compares well with the highly sensitive phytoplankton alga Emiliania huxleyi whose growth was reported to be halted at a daily, weighted BEDDNA300 nm of 0·4 kJ m−2 administered during 4 days for 3 h in the middle of the light period.

Eighteen collections of red-coloured Audouinella from Central Mexico and southeastern Brazil detected three species. The most common species, A. eugenea, is characterized by macroscopic thalli, the erect system consisting of filaments with cylindrical cells, undifferentiated into proximal and distal parts, and relatively large monosporangia ([ges ] 12·0 μm long). Spermatangia and possible propagules were observed in some Mexican populations. This is the third Audouinella species observed to have gametangia and the first member of the Acrochaetiales with putative propagules. The second species, from Central Mexico, was characterized by the following features: macroscopic thalli, the erect system differentiated into proximal parts with cylindrical cells, unbranched or rarely branched, and distal parts with barrel-shaped cells, abundantly branched to form dense fascicles, with alternate or dichotomous branching, some at right-angles to the axis, and relatively large monosporangia ([ges ] 12·0 μm long). The morphologically distinct proximal and distal portions of the erect system, the latter forming dense fascicles, was a consistent character so far unknown in Audouinella; thus, we propose a new species, A. huastecana sp. nov. The third species is a microscopic epiphyte, A. meiospora, with a well-developed prostrate system composed of creeping and loosely aggregated filaments, and a short homogeneous erect system ([les ] 15 cells) of filaments with cylindrical or barrel-shaped cells and small monosporangia ([les ] 13·0 μm long). A. eugenea and A. meiospora are characterized for the first time from the Southern and Northern Hemispheres, respectively, both occurring mostly in areas of tropical or subtropical rainforests. A. meiospora is reported from new macroalgal hosts. A. eugenea and A. huastecana tended to occur in warm, alkaline waters with a high ion content that were moderate to fast flowing, whereas A. meiospora was not associated with particular habitats.

An image analysis system was used to count and measure acetoorcein-stained mitotic chromosomes of the acidothermophilic unicellular red algae Galdieria maxima, G. partita, G. sulphuraria and Cyanidium caldarium (Cyanidiophyceae). Chromosome numbers fell into two groups: n = 2 for all three species of Galdieria and n = 5(7) for C. caldarium. It seems that a separation of C. caldarium from Galdieria is karyologically justified. A chromosome number of 2 appears to be indicative of the genus Galdieria and could be used as a marker to distinguish this taxon from Cyanidium. The two smaller chromosomes in the karyotype of C. caldarium were about 0·4 μm long whereas the other three were 0·5–0·7 μm long. In karyotypes of Galdieria species, the two chromosomes differed in length, the smaller chromosome ranging from 0·8 to 1·8 μm and the larger one from 1·2 to 2·3 μm. The visualization of these extremely small chromosomes was possible due to pretreatment of the cells with the DNA intercalator 9-aminoacridine. The mean absolute length of each chromosome of the three members of Galdieria had statistically significant interspecies differences. Nuclear 1C DNA contents were estimated in the algal cells by the Feulgen technique. All species investigated had genome sizes of 1·50–2·25×10−2 pg. Thus it seems that the members of Cyanidiophyceae have the smallest known genomes of all photosynthetic eukaryotes.

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.

There is increasing evidence that bacterial–algal interactions play a role in Harmful Algal Bloom (HAB) ecology. Bacteria that are associated with bloom-forming algal species, specifically toxic dinoflagellate algae, have been implicated in the production and biotransformation of paralytic shellfish toxins (PSTs). To clarify the role that these bacteria may play in the production of PSTs, it is desirable to identify and localize the bacteria associated with the dinoflagellates and enumerate them during the course of the algal blooms that the toxic dinoflagellates produce. Because 16S rRNA-targeted probes offer the possibility of both, we previously made and tested probes for some putatively toxigenic bacteria isolated from cultures of the PSP-related dinoflagellates Alexandrium tamarense, A. affine and A. lusitanicum. The bacteria isolated from the dinoflagellates belong primarily to the alpha-proteobacterial group of Roseobacter and the gamma-proteobacterial group of Alteromonas. Here, we report the successful application of these probes to Lugol's-fixed seawater samples. We detected these bacteria in high numbers in the water column when Alexandrium spp. were both present and absent, and during periods when mussels contained PSTs.

The stimulating effect of blue light on the carbon-concentrating mechanism of Ectocarpus siliculosus was investigated by measuring the intracellular pools of inorganic carbon (Ci) in red light (low photosynthetic rates) and in red light plus blue light (high photosynthetic rates). Ci accumulated in red light to about twice the levels found in the presence of blue light, but the permeability of the cell membranes for Ci, measured as the rate of influx of tracer carbon, was similar in both light conditions. This was also true after the seawater pH was adjusted to pH 9·5, when bicarbonate should be the only inorganic carbon species to enter the cells. Activation of photosynthesis after prolonged red light caused the accumulated Ci to decline to levels similar to those observed in blue light. The time course of this decline was rapid and coincided with the time course that was expected for the emptying of a carbon pool whose existence had been demonstrated earlier in measurements of photosynthetic oxygen evolution in the absence of external carbon. The accumulation of Ci in red light required active photosynthesis, but it also occurred in the presence of inhibitors of carbonic anhydrase activity. It is suggested that blue light mobilizes the Ci pool by causing changes in intracellular pH and that the size of the pool depends on the activity of metabolic CO2-sink activities that are also under the control of blue light.

Marked seasonal reproduction is a widespread phenomenon in seaweeds in temperate waters strongly influenced by seasonal variations. In the Baltic Sea, however, the perennial brown alga Fucus vesiculosus exhibits two periods of reproduction: early summer (May–June) or late autumn (September–November). In this study, we compared the geographical distribution, the reproductive biology and the recruitment success for F. vesiculosus that reproduce during either of these two periods on the east coast of Sweden. Both monocultures and mixed populations of summer- and autumn-reproducing F. vesiculosus occurred along the mainland coast from the southern parts of the Stockholm archipelago to the southernmost part of Sweden. F. vesiculosus reproduced only during summer around the coasts of the large islands of Öland and Gotland. After reproduction, in July and January respectively, plants that reproduced in summer abscised their receptacles and part of their branches, while plants reproducing in autumn abscised only their receptacles. In laboratory experiments, short-day treatments (light:dark 8:16 h) were shown to initiate receptacles in summer-reproducing plants, whereas plants reproducing in autumn initiated receptacles independently of short- or long-day (light:dark 16:8 h) treatment. Plants reproducing during summer produced more eggs (21·0×104 eggs/g−1 frond mass) of smaller size (0·067 mm) than plants reproducing during autumn (8·9×104 eggs/g−1 frond mass, egg size 0·070 mm). However, recruitment success in the field was similar irrespective of the period of reproduction. The differences in the photoperiodic response, the differences in reproductive output and egg size between summer and autumn plants, and the observation that a single individual kept the same pattern of reproduction over a period of at least three reproductive seasons, may indicate that the two strategies of reproduction in F. vesiculosus are expressions of two distinct genotypes.

The only eukaryotes found in highly acidic environments (pH 0·5–3) with elevated temperatures (up to 56 °C) are three species of unicellular red algae: Cyanidioschyzon merolae, Cyanidium caldarium and Galdieria sulphuraria. These habitats are scattered all over the world and are usually very small. Because all three species are strictly acidophilic and will not tolerate desiccation, distribution by wind or water seems very unlikely. The populations in the various habitats might have been isolated for very long times, providing a unique opportunity to observe a significant degree of independent evolution under strong selective pressure. We investigated the biogeography of 18 isolates of these red algae by comparison of partial sequences of the 18S rRNA. A gene tree based on 18S rRNA assigns 15 strains to one branch with high bootstrap values. These isolates share the feature of facultative heterotrophy, whether or not they were originally placed in the genus Galdieria. The remaining three strains – Galdieria maxima, C. merolae and C. caldarium – form a sister clade to this group. The exact position of these two groups in relation to other red algae remains unresolved. The evolutionary distance between individual Galdieria strains is high, indicating that within this genus several races have developed significantly altered 18S sequences. Our comparison of 18S sequences from thermo-acidophilic red algae indicates that even within a seemingly homogeneous group of eukaryotic organisms the limits of phylogenetic analysis may be reached.