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.

Daily integrals of photosynthesis by a cyanobacterial bloom in the Baltic Sea, during the summer of 1993, were calculated from the vertical distributions of light, temperature and the organisms in the water column and from photosynthesis/irradiance curves of picoplanktonic and diazotrophic cyanobacteria isolated from the community. The distribution of chlorophyll a in size-classes < 20 μm and > 20 μm was monitored over 9 days that included a deep mixing event followed by calm. Picocyanobacteria formed 70% of the cyanobacterial biomass and contributed 56% of the total primary production. Of the filamentous diazotrophs that formed the other 30%, Aphanizomenon contributed 28% and a Nodularia-containing fraction 16% of the primary production. For the whole population there was little change in standardized photosynthetic O2 production, which remained at about 31 mmol m−2 before and after the mixing event. There were differences, however, between the classes of cyanobacteria: in picocyanobacteria primary production hardly changed, while in Aphanizomenon it increased by 2·6 and in Nodularia it fell below zero. Total phytoplankton photosynthesis was strongly dependent on total daily insolation with the compensation point at a photon insolation of 22·7 mol m−2 d−1. Similar analyses of N2 fixation showed much less dependence on depth distribution of light and biomass: Aphanizomenon fixed about twice as much N2 as Nodularia their; their fixation exceeded their own N demand by about 12%. Together, these species contributed 49% of the total N demand of the phytoplankton population. Computer models based on the measured light attenuation and photosynthetic coefficients indicate that growth of the cyanobacterial population could occur only in the summer months when the critical depth of the cyanobacteria exceeds the depth of mixing.

Morphological characters and growth rates of Ascophyllum nodosum were compared on fronds collected from different shore levels at one site in Strangford Lough, Northern Ireland. Both the bladders and axes of thallus tips were smaller and less variable on the upper shore than on the middle and lower shores, and the proportion of biomass invested in the production of bladders was smaller. The axes of upper shore plants were wider and flatter than on the lower shore, and the bladders were also relatively flat on the upper shore but more rounded on the lower shore. The maximum age of unbroken fronds, as estimated from the number of air bladders, was 6 years on the upper shore and 17 years on the lower shore, indicating the higher probability of breakage of plants caused by stress on the upper shore. In situ growth rates of individually marked plants along a vertical shore transect were monitored at 2- to 4-week intervals for 31 months. Length increase was highest (16 cm yr−1) in the middle of the Ascophyllum nodosum zone, and lowest (10 cm yr−1) on the upper shore. Growth was strongly seasonal with low (but not zero) growth rates during November and December, and highest growth rates in late spring and early summer. A decline in growth in mid-summer was observed at all shore levels. Growth was positively correlated with sunshine hours and total solar irradiance in winter and spring but there was no correlation with these factors during summer months. Maximum daily temperatures had a positive influence on growth in late spring, but no effect in the rest of the year. In transplantation experiments conducted in summer and winter, 80% of plants moved from the lower to the upper shore died within 3 months, whereas all transplants from the upper to the lower shore and all controls survived. Growth rates of surviving transplants at both shore levels were similar to those of control plants at the same shore level in the summer experiment. The pigment content and photosynthetic capacity of surviving plants acclimated to ambient conditions and, after 3 months, were not significantly different from those of control plants at the same shore level. It is suggested that the phenotypic acclimation of physiological characteristics and the genetic adaptation of morphological features contribute to the ability of this species to dominate such a wide band in the intertidal zone of sheltered rocky shores in the North Atlantic.

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.

In this paper we quantify the interactive effects of wave exposure and intraspecific density on the survivorship and growth of Sargassum muticum in northern Spain. Juveniles settled onto slate plates were experimentally thinned to two densities and transplanted to exposed and sheltered shores. Initially, plants grew faster at the exposed sites but final lengths were similar between exposures after 5 months, largely because of breakages at the top of the main primary lateral of plants at exposed sites. Mean weights of plants did not significantly differ between exposures. The results indicate that S. muticum juveniles growing at high density were longer and thinner but similar in weight to those at low density. Patterns of growth of larger plants transplanted between sheltered sites similarly suggested changes in morphology of S. muticum in response to differences in density. Survivorship of juveniles did not differ between exposures but was significantly poorer at the higher density irrespective of wave exposure. The results of this and previous studies suggest that the abundance of S. muticum in the low intertidal area of exposed shores in northern Spain is limited at several life-history stages. The relative importance of these potential bottlenecks compared with the availability of propagules remains unknown.

Laurencia Lamouroux subgenus Chondrophycus Tokida et Saito was recently raised to generic status as Chondrophycus (Tokida et Saito) Garbary et Harper (Ceramiales, Rhodophyta). The previously unknown morphology and anatomy of two Chondrophycus species, C. undulata (Yamada) Garbary et Harper and C. parvipapillata (C.K. Tseng) Garbary et Harper, were studied in specimens from Korea, Japan and Hawaii. These species share some features, such as a strongly compressed thallus, vegetative axes with two pericentral cells, tetrasporangial production from pericentral cells and spermatangial development of the trichoblast type. However, they differ from each other in the position of the first pericentral cell relative to the trichoblast in axial segments and in the position of the tetrasporangial pericentral cell. In C. undulata, the first pericentral cell is always produced at one side of the basal cell of a trichoblast, whereas in C. parvipapillata it is formed underneath this cell. While tetrasporangia in C. undulata are produced only from three (occasionally four) additional pericentral cells, in C. parvipapillata they are formed by the existing second pericentral cell and two (occasionally three) additional pericentral cells, so the resulting tetrasporangial axial segment has only one sterile pericentral cell rather than two as in C. undulata. C. undulata produces spermatangial branches from two laterals on the suprabasal cell of trichoblasts but one of the two remains partly sterile, whereas in C. parvipapillata a spermatangial branch develops from only one of the two laterals. These two species also differ distinctly from each other in some vegetative features, such as presence or absence of (1) secondary pit connections between epidermal cells, (2) a palisade structure of epidermal cells with conical projections and (3) corps en cerise. The taxonomic implications of these vegetative and reproductive features of Chondrophycus and those of other genera of the Laurencia complex necessitate changes to the generic delineations of Osmundea Stackhouse, Laurencia and Chondrophycus. The required new combinations in Chondrophycus are made, mainly for species from the western Pacific. An infrageneric classification scheme is also proposed for Chondrophycus including Kangjaewonia subgen. nov., Palisada (Yamada) subgen. stat. nov., Yuzurua subgen. nov. and Parvipapillatae sect. nov.

Volcanic areas with highly acidic solfatara soils and temperatures of up to 56 °C are inhabited by the red algal genus Galdieria. We examined three highly acidic but non-volcanic habitats in the western part of the Czech Republic for the occurrence of this red alga. In soil samples from the National Nature Reserve of Soos we found, together with Euglena mutabilis, Pseudococcomyxa simplex and species of Chlorella, a new strain of Galdieria. In contrast to all other Galdieria strains described so far, the strain from Soos exhibited a low temperature optimum for growth of about 30 °C. Other properties, such as the substrate spectrum for heterotrophic growth, ultrastructure, fatty acid composition, thermostability of enzymes and the nitrogen source, showed no obvious differences from other strains of Galdieria. Within a phylogenetic tree based on 18S rRNA sequence data, the strain from Soos occupied a position at the base of the ‘Galdieria’-branch. Our findings indicate that the genus Galdieria is not restricted to volcanic and mining areas and that strains of Galdieria are able to compete successfully with green algae in habitats like Soos.

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.

The ultrastructure of Peridinium cinctum, was examined by serial sectioning with particular emphasis on the detailed construction of the flagellar apparatus. The pusular system of P. cinctum included two sac pusules in open connection with the flagellar canals; disorganized material was found inside the pusules and near the flagellar pores, indicating excretory activity of the pusules. Several cells had replicated basal bodies, which were oriented toward the cell apex. The functional basal bodies formed an angle of about 65° and were linked by a layered connective, a structure so far seen only in peridinioids. A transverse microtubular root looped around the transverse flagellar canal and nucleated several rows of microtubular extensions that lined most of the transverse sac pusule. A single-stranded root was associated with the surface of the longitudinal basal body almost at a right angle to the basal body triplets. A fibrous connective between the transverse striated root and the longitudinal microtubular root was absent. The striated collars encircling the flagellar pores had a complex structure and were linked by a large connective; a smaller fibrous connective was also found in one cell. An extension of the longitudinal striated collar lined part of the longitudinal sac pusule; it showed a tubular substructure and was perhaps contractile. Bacteria were present in the peripheral cytoplasm of the cell, enveloped by several unit membranes and surrounded by vacuoles; near the sac pusules they appeared disorganized with aggregated ribosomes, possibly the result of digestion.

Bacteria associated with toxic algae in culture have been implicated in the enhancement of algal toxin production and auto-toxigenesis. Toxigenic and non-toxigenic bacterial isolates from Alexandrium spp. have been determined to belong predominantly to the α- and γ- subclasses of the class Proteobacteria. Within these subclasses, the isolates were further classified into two clades that were phylogenetically affiliated with (1) the genus Roseobacter, a newly identified group that is of major significance within the α-Proteobacteria and (2) the genus Alteromonas. Specific 16S rRNA sequence signatures were identified for these clades as well as for three pairs of isolates and for one subcluster within the Roseobacter clade and for three clusters representing eight isolates in the Alteromonas clade. Oligonucleotide probes complementary to these regions were designed and their specificities were tested using dot-blot and whole-cell in situ hybridizations of target and non-target strains. The empirically determined dissociation temperatures of the probes ranged between 55 and 65 making them applicable as a set for screening environmental samples. In situ hybridization of bacteria in cultures of Alexandrium spp. with the clade-specific probes showed a loose association of these bacteria within the phycosphere. In addition, the fluorescent signal of the probes was bright and easily distinguishable from autofluorescent bacteria and the dinoflagellates.

The identity of Dinophysis sacculus Stein has proved to be problematic in recent years, during which this species has been associated with diarrhoetic shellfish poisoning (DSP) events along European coasts. To complement the scarce and at times contradictory existing information, we provide details of morphological variation in D. sacculus throughout its geographical range, which includes the Mediterranean Sea and European Atlantic coasts. Our data clarify its relationship with D. pavillardii Schröder. This species differs from D. sacculus only by the presence of a concavity along the dorsal margin, but transitional morphotypes are frequent in almost all the samples examined. We therefore propose merging the two species and classifying morphotypes with a dorsal concavity as D. sacculus f. reniformis (Pavillard) comb. nov. Despite the high variability of Dinophysis sacculus, it was generally possible to separate it from D. acuminata Claparède & Lachmann. The only character distinguishing the two species is the shape of the large hypothecal plates, which in D. sacculus are elongate, almost rectangular or sac-like, whereas in D. acuminata they are shorter, more convex dorsally and often more slender towards the antapex. Thecal areolation and sulcal list ornamentation are more pronounced in D. acuminata, although these characters are somewhat variable. Other thecal details, such as the shape of sulcal platelets and the structure of the apical pore area, were not useful for circumscription of the two taxa. In a few samples from the Galician Rias and from the Spanish Mediterranean coast, we observed morphotypes intermediate between D. sacculus and D. acuminata, which indicates that the two species can have slightly overlapping ranges of variability.

Macroalgal assemblages of Posidonia oceanica rhizomes of the western Mediterranean have been studied, in order to describe the structure of this community and to evaluate changes due to recent macroalgal invasions. To achieve these objectives, P. oceanica rhizomes were sampled from 21 beds distributed throughout the western Mediterranean Sea and macroalgal assemblages were studied using both species and functional groups as descriptors. Moreover, modifications linked to temporal fluctuations and depth were evaluated in an insular and in a continental bed. A total of 74 macroalgal species were found, among them 7 Chlorophyta, 8 Fucophyceae and 59 Rhodophyta. The species number varied from 5±0 at Vada to 18±0·58 at Panarea Island. The total percentage cover ranged from 19·5±1·8 at Cabo de Creus to 77·2±13·3 at La Maddalena Island. Filamentous species were dominant in the localities colonized by Acrothamnion preissii or Womersleyella setacea, while a high functional diversity occurred where the two introduced species were not present or they did not constitute dense turfs; the importance of crustose and foliose species was remarkable, while low cover of articulate and corticated-terete species was found at all localities. Localities where turfs were not developed were grouped together, even if they appeared more dispersed than those dominated by filamentous algae. The two beds studied over a 1 year period showed higher values of macroalgal cover in March and December, although significant differences were not detected with ANOVA in relation to either depth or season. The development of turfs, which occurs widely in western Mediterranean seagrass beds, seems to modify strongly the structure of macroalgal assemblages of rhizomes, mostly via the decrease in species and functional diversity.

The unicellular, acido- and thermophilic red alga Galdieria sulphuraria is unique in its ability to grow heterotrophically on at least 27 different sugars and polyols. The enzymatic machinery necessary for metabolizing this variety of compounds is constitutively expressed in the alga. The uptake system, however, has to be induced. From in vivo studies we conclude that the uptake system consists of several transporters with a partly overlapping substrate specificity. These transporters can be grouped into hexose, polyol and pentose transporters. The mode of induction depends on the substrate supplied for heterotrophic growth. When autotrophic cells were supplied with hexoses, hexose and polyol transporters were induced from the onset of heterotrophic conditions. Depletion of substrate in the medium triggered the induction of other transporters. Dulcitol, as well as other polyols and pentoses, led to a co-induction of all transporters as judged from induction and competition experiments. The heterotrophic capabilities of Galdieria are intriguing, because the natural habitat of the alga contains only traces of organic carbon. The substrates for heterotrophic growth apparently originate from decaying cells releasing hydrolysed cell material. Trace amounts of glucose were sufficient for the induction of sugar uptake in Galdieria. The co-induction of transporters obviously enables the cells in endolithic mats to import a wide spectrum of organic carbon in order to survive periods of light limitation.

The combination of nitrogen deprivation and increased cultivation light intensity resulted in the synthesis of secondary carotenoids in flagellates of Haematococcus lacustris. The pigment pattern was characterized by high-pressure liquid chromatography analysis during the accumulation period and in response to inhibitors of carotenoid biosynthesis (diphenylamine, norflurazon and tetcyclacis). Diphenylamine treatment resulted in (i) a decrease in ketocarotenoids and (ii) an accumulation of β-carotene and zeaxanthin due to inhibition of the β-carotene oxygenase. Our results indicate that astaxanthin synthesis in H. lacustris follows the biosynthetic pathway elucidated in the marine bacterium Agrobacterium aurantiacum.

In the course of the cell cycles of synchronous cultures of the chlorococcal alga Scenedesmus quadricauda, the following were monitored: total protein and RNA accumulation as a measure of growth processes, the timing of the commitment points at which the cells trigger the sequence of reproductive processes (DNA replication, nuclear and cellular division) and the course of the reproductive processes. The synchronous cultures were grown either under various lighting regimes, or in the temporary presence of specific inhibitors of either proteosynthesis (cycloheximide) or DNA replication (5-fluorodeoxyuridine). By adjusting the length of the light period, the cell cycle could be manipulated. Cell cycle patterns could be altered to give different numbers of sequences of reproductive processes. The extent of their mutual overlap could be influenced and the number of daughter cells produced could be altered. Schematic illustrations of various cell cycle patterns and comparisons with those of higher plants and other algal species are presented.

Annual growth per plant and allocation of growth to the stipe were measured in 2- to 4-year-old plants of Laminaria hyperborea from five stations with different degrees of wave exposure and different amounts of canopy biomass. Low growth in plants with initial stipe lengths of less than about 40 cm suggested that the presence of canopy-forming plants suppresses growth of understorey plants, and this was supported by the high lamina growth rate of understorey plants after removal of the canopy-forming plants. Canopy biomass and wave exposure were found to exert a differential effect on the growth of the age groups examined. Average annual growth per plant in 2- to 3-year-old plants decreased with increasing canopy biomass; growth of 4-year-old plants was not significantly influenced by canopy biomass, but increased with increasing wave exposure of the sites, suggesting an influence of some factor connected with wave exposure. The allocation of annual growth to stipe and lamina was also found to be influenced by canopy biomass and wave exposure. In 2- to 3-year-old plants the amount of annual growth allocated to the stipe increased with increasing canopy biomass while a positive linear regression between allocation of growth to the stipe and wave exposure was found in 4-year-old plants. Individual measurements carried out at a wave-exposed locality showed that the maximum allocation of growth to the stipe in the intermediate-sized plants occurred simultaneously with a period of rapid stipe elongation. Thus, rapid stipe growth in L. hyperborea can be associated with high allocation of annual growth to the stipe when the plants are about to grow into the canopy-forming layer. We suggest that this is due to the combined effects of suboptimal light levels within the kelp forest and high wave exposure.

Monoecious, bisexual and unisexual clones of Achnanthes longipes were isolated from the Black Sea and studied in laboratory culture. Clones differed in their growth characteristics: in monoecious clones the cells formed tufted aggregations while in other clones they were more dispersed. Bisexual and unisexual clones exhibited intraclonal (monoecious) reproduction, but only at a very low frequency and usually within a more restricted size range than in monoecious clones. Interclonal crosses were made in all possible pairwise combinations. Abundant auxosporulation took place in all crosses, except where unisexual clones of the same sex were incubated together. Auxosporulation was more vigorous and occurred over a wider size range in interclonal crosses than during monoecious reproduction. Sexual reproduction is isogamous. In the commonest pattern of auxosporulation, two paired gametangia each produce two gametes, which fuse to give two auxospores. More rarely (9% of pairs), the gametangia produce only one gamete apiece, and hence only one auxospore. In addition, very small cells can enlarge vegetatively, although genetic or cytological damage sometimes compromises their long-term viability.

Nostoc punctiforme is the microsymbiont of the unique fungal endocyanosis Geosiphon pyriforme. During the establishment of this endosymbiosis fungal hyphae incorporate a specific stage of the N. punctiforme life cycle, formed during differentiation from the motile hormogonium to the non-motile primordium stage. The life cycle of N. punctiforme was synchronized by first inducing hormogonium differentiation by red light illumination for 36 h, followed by applying light/dark cycles for 96 h. Different developmental stages of N. punctiforme including hormogonia, primordia and vegetative colonies were analysed by fluorescein isothiocyanate (FITC)-conjugated lectins with sugar specificity to α-D-mannose/α-D-glucose, N-acetyl-β-D-glucosamine oligomers, α-L-fucose, β-D-galactose, α-D-galactose, N-acetyl-α-D-galactosamine and sialic acid. Lectin binding properties indicate that the slime produced by the motile hormogonia contains β-D-galactosyl and α-L-fucosyl residues, which disappear during further development. There is a clear correlation between the transition from the hormogonium to the non-motile primordium stage and the appearance of a large amount of α-D-mannosyl (or α-D-glucosyl) residues in the extracellular slime. This strongly Concanavalin A (Con A)-positive compound is lost in part during later differentiation into vegetative colonies. Consequently these significant changes in the Nostoc slime, occurring at the developmental stage involved in the establishment of the Geosiphon symbiosis, could play a role in the specific recognition between the symbiosis partners.

Response of Aphanizomenon ovalisporum to certain environmental parameters was studied to gain a better understanding of the conditions which may have stimulated its autumnal bloom in Lake Kinneret. Optimal temperature for A. ovalisporum growth was 26–30 °C, resulting in growth rates of 0·2–0·3 day−1, similar to those observed in the lake. Maximal rate of CO2 fixation (assimilation numbers of 6–8 μg C μg−1 Chl h−1) was obtained at low irradiances (Ik of 40–100 μmol photons m−2 s−1), 200 μM Pi and low N[ratio ]Pi ratios. Growth was strongly affected by phosphorus availability, reaching a maximum at Pi concentrations above 40 μM. The high demand for phosphorus was indicated by an increase in alkaline phosphatase activity. The relative abundance of Pi in the cells increased by 4-fold in Pi-rich compared with Pi-limited cultures. Uptake of Pi was faster in Pi-depleted compared with Pi-sufficient cells. Maximal photosynthetic rates and K1/2(HCO-3) were 140–220 μmol O2 mg−1 Chl h−1 and 10–24 μM, respectively. At pH 7·0 the K1/2(CO2) was 2·2 and fell to 0·04 μM at pH 9·0. These data indicated that A. ovalisporum is a HCO-3 user, and can explain its high photosynthetic rates during the bloom, under high pH and low dissolved CO2 conditions. Na+ concentrations of about 5 mM were essential for A. ovalisporum growth at high pH approaching values in the lake.

The influence of culture conditions on the biosynthesis and degradation of polysaccharides (starch and carrageenan) in the red alga Solieria chordalis was investigated. Following 1 week of incubation in the dark, the alga synthesized floridean starch at two irradiances, 50 and 480 μmol photons m−2 s−1 (400–700 nm), in nutrient-unenriched seawater. Upon transfer of these cultured algae to nutrient-enriched seawater at 50 μmol photons m−2 s−1, the stored floridean starch was found to break down. 14C labelling revealed that during floridean starch breakdown the tracer was transferred to carrageenan. These results are interpreted as carbon transfer from stored floridean starch for use in carrageenan biosynthesis.