The algal vegetation of five diving profiles situated at exposed sites of the outer Öregrund archipelago, southern Bothnian Sea, Sweden, was investigated by SCUBA diving in 1996. The vegetation of the same profiles had been described earlier in 1943–4 and 1984. In the present study, special attention was paid to the occurrence of the structurally important belt-forming brown algae Fucus vesiculosus and Sphacelaria arctica in comparison with the situation 52–53 and 12 years earlier. Prominent differences between the 1940s and 1996 were found. The weighted average depth of the F. vesiculosus belt in 1996 was about 1·7 m shallower than in the 1940s, and the lower distribution limit of this species was about 2·5 m shallower. At its lower end the Fucus belt was replaced by epilithic red algae, mainly Furcellaria lumbricalis, Rhodomela confervoides and Polysiphonia fucoides. These results were similar to those of the 1984 study and show neither an improvement nor a deterioration of the belt during the past 12 years. In four of the five diving profiles, a conspicuous belt of S. arctica occurred in the lower sublittoral, similar to that observed in the 1940s, but in one of the five profiles the S. arctica belt was heavily impoverished. These results contrast with the 1984 study which reported that S. arctica had practically disappeared from all profiles. The epiphytic cover of annual filamentous algae, dominated by Pilayella littoralis and Ceramium gobii, was higher in 1996 than in 1943–4. The results of this comparative study are discussed in relation to the general eutrophication of the Baltic Sea.

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.

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 green alga Chlamydomonas reinhardtii can use the ureides allantoin and allantoate as sole nitrogen sources. Once the uptake systems for allantoin and allantoate were induced, the uptake and growth rates were identical for the two ureides. However, the enzymatic activities involved in the degradation of the two ureides (allantoinase and allantoicase) were regulated differently. Allantoinase seems to be constitutive, since it was detected in all the nitrogen sources studied, while allantoicase behaved as an inducible enzyme, since it was present only in cells cultured in ureides or any metabolic precursor of these compounds. Neither allantoinase nor allantoicase activities were repressed by ammonium in the presence of ureides. Allantoicase activity was not induced under nitrogen starvation conditions, while it was induced in cells that had been cultured with allantoin or allantoate in the dark. Allantoin uptake showed a pattern similar to that of allantoate under all nutritional and environmental conditions tested. Inhibition of allantoin and allantoate uptake by N-ethylmaleimide suggests that thiol (SH–) groups are involved in both uptake systems. The use of both allantoin and allantoate was similarly inhibited by the metabolic poisons tested (cyanide, azide, 2,4-dinitrophenol and 3′-(3,4-dichlorophenyl)-1′,1′-dimethyl urea) but only at very high concentrations. The possibility that uptake of allantoin and allantoate might take place through two independent systems is discussed.

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.

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.

The brown algal family Chordaceae contains the single genus Chorda with two terete unbranched species, C. filum and C. tomentosa. They share a similar superficial morphology, but differences in anatomy and reproductive characters have made assignment to a single genus controversial. Comparison of DNA sequences of variable parts of the small subunit of the nuclear ribosomal cistron, and of relatively conserved areas of both internal transcribed spacers, of several taxa of the Sporochnales–Desmarestiales–Laminariales complex revealed that the two species of Chorda are not closely related and do not form a clade. This is taken as support for recognition of Halosiphon tomentosus (Lyngbye) Jaasund, although it was originally based on the erroneous observation of a Streblonema-like gametophyte in the life history of H. tomentosus.

Detailed studies on the sporophytes and gametophytes of Dictyopteris australis and Dictyopteris muelleri from Australia have demonstrated the usefulness of several reproductive characters in species discrimination. In D. australis, spherical sporangia that project above the thallus surface and are clustered around reflexed bundles of paraphyses contrast markedly with the angular sporangia of D. muelleri, which are embedded in the thallus and are scattered in broad fertile zones on the upper branches. In D. muelleri, tetrads of released spores enveloped by the inner sporangial wall are temporarily retained above the thallus surface on the ends of mucilaginous stalks. Sporangial stalks have not been reported in any other species of the brown algae, although egg stalks are produced by several fucalean species. Differences in oogonial structure can also be used to distinguish D. australis and D. muelleri. The spherical oogonia of D. australis, which project above the thallus surface, are conspicuously different from the angular embedded oogonia of D. muelleri. Detailed comparative studies on other species of Dictyopteris are now required to ensure that reproductive characters are used not only to define species of Dictyopteris but also to effectively circumscribe the genus.

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.

The Japanese endemic charalean species Nitella gracilens Morioka (=N. furcata subsp. furcata var. sieberi f. gracilens) was thought to be extinct until it was rediscovered at the type locality, Lake Ashinoko, Kanagawa Prefecture. Uni-charalean cultures of N. gracilens were established and sexual organs developed and matured. The morphology of this alga, examined by light microscopy, corresponds closely with the original description by Morioka, particularly with regard to the oospores. The mature oospore walls of N. gracilens are orange or yellowish-brown and the fossa wall of the oospore is smooth or has a finely granulate ornamentation. In addition, scanning electronic microscopic examination demonstrated that the fossa walls have minute granulate structures that are compactly arranged. These observations contrast with a previous report that the oospore wall ornamentation of this taxon is reticulate. Since oospore wall ornamentation and the form of the dactyls in N. gracilens are essentially different from those of other infraspecific taxa of N. furcata sensu Wood (1965), N. gracilens should be maintained as a distinct morphological species within the genus Nitella.

Ulva armoricana sp. nov. is described from the coast of Brittany, France, using the taxonomic criteria established by Bliding, Koeman and van den Hoek for the European species of Ulva. Morphological evidence strongly suggests that Ulva armoricana is conspecific with the free-living Ulva populations responsible for the ‘green tide’ phenomenon that occurs at some eutrophicated sites in North Brittany. Blades of U. armoricana are variable in shape, fragile, easily torn, and 30–55 μm thick in middle and apical regions; they differ from those of U. olivascens by their pale green colour and from those of Ulva lactuca, U. rotundata, U. gigantea, U. pseudocurvata and U. curvata by their crumpled texture that creates an irregular light-reflecting surface, and by the presence of tooth-like protuberances at the margin of the blade. U. armoricana differs from U. scandinavica in having longitudinal ribs containing closely packed bundles of rhizoids, except in the youngest thalli. U. armoricana can be discriminated from U. rigida by the polygonal (never rounded) cells in the mid-thallus region, and quadrangular cells arranged in small longitudinal rows in rapidly growing parts. Pyrenoid number, 1–2 (3–4), overlaps with that of other species, and shape of non-rhizoidal cells of the basal region in transverse sections, either oval or with tapered ends, appears not to be a good taxonomic character. Herbarium data indicate that the species has been collected in northern France since at least 1869, but was previously unrecognized.

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.

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.

The utility of rDNA internal transcribed spacer (ITS) sequences for separating species of Ulva along the North Brittany coast of France was investigated. Particular attention was paid to the Ulva species responsible for ‘green tides’. Floating thalli are difficult to identify due to fragmentation and it was not clear at the outset whether one or more species of Ulva might be contributing to the green tide phenomenon. Results show that ITS sequences are good markers for Ulva species and that the Lannion Bay green tide taxon is a previously unrecognized species that can also be identified on morphological grounds. We found that ITS type did not necessarily correspond to the initial identification of a specimen based on morphological features, due to the lack of good diagnostic characters. This survey highlights the need for a more intensive survey of Ulva populations along European coasts. Once ITS groups can be recognized, quick screening assays can be developed to aid morphological identification.

Production of phytochelatins (PCs) in response to cadmium uptake in the benthic macroalgae Vaucheria compacta and V. debaryana (Xanthophyceae) was investigated. The algae synthesized thiol-containing peptides, identified by means of high-performance liquid chromatography as PC2, PC3 and PC4. In both algal species the level of PCs increased with time of cadmium exposure and was dependent on external cadmium concentration. V. compacta synthesized significantly more PCs than V. debaryana. Exposure of the algae to cadmium at low temperature and in darkness resulted in a significant decrease in PC content over the time interval tested (3 days).