A compilation of data on the elemental composition of marine phytoplankton from published studies was used to determine the range of C[ratio ]N[ratio ]P. The N[ratio ]P ratio of algae and cyanobacteria is very plastic in nutrient-limited cells, ranging from <5 mol N[ratio ]mol P when phosphate is available greatly in excess of nitrate or ammonium to >100 mol N[ratio ]mol P when inorganic N is present greatly in excess of P. Under optimal nutrient-replete growth conditions, the cellular N[ratio ]P ratio is somewhat more constrained, ranging from 5 to 19 mol N[ratio ]mol P, with most observations below the Redfield ratio of 16. Limited data indicate that the critical N[ratio ]P that marks the transition between N- and P-limitation of phytoplankton growth lies in the range 20–50 mol N[ratio ]mol P, considerably in excess of the Redfield ratio. Biochemical composition can be used to constrain the critical N[ratio ]P. Although the biochemical data do not preclude the critical N[ratio ]P from being as high as 50, the typical biochemical composition of nutrient-replete algae and cyanobacteria suggests that the critical N[ratio ]P is more likely to lie in the range between 15 and 30. Despite the observation that the overall average N[ratio ]P composition of marine particulate matter closely approximates the Redfield ratio of 16, there are significant local variations with a range from 5 to 34. Consistent with the culture studies, lowest values of N[ratio ]P are associated with nitrate- and phosphate-replete conditions. The highest values of N[ratio ]P are observed in oligotrophic waters and are within the range of critical N[ratio ]P observed in cultures, but are not so high as to necessarily invoke P-limitation. The C[ratio ]N ratio is also plastic. The average C[ratio ]N ratios of nutrient-replete phytoplankton cultures, oceanic particulate matter and inorganic N and C draw-down are slightly greater than the Redfield ratio of 6·6. Neither the analysis of laboratory C[ratio ]N[ratio ]P data nor a more theoretical approach based on the relative abundance of the major biochemical molecules in the phytoplankton can support the contention that the Redfield N[ratio ]P reflects a physiological or biochemical constraint on the elemental composition of primary production.

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 population of Stephanodiscus rotula in a temperate eutrophic lake was studied over a 2 month period (January to early March). Although during the study period nutrient concentrations in the lake water remained far in excess of phytoplankton requirements, no notable increase in chlorophyll levels was recorded. This suggests that algae were limited by shortage of light and low temperatures. Frequency distribution analysis of cell diameters showed a dramatic size reduction at the end of winter, followed by restoration of higher values by early spring. Electron probe X-ray microanalysis spectra from Stephanodiscus cells routinely showed peaks of Ca, K, Si, P, S, Fe, Al, Mn, Mg, Na and Cl, with substantial variation in elemental concentrations both between and within samples. End-of-winter reduction in the cell size coincided with a considerable depletion of intracellular chemical levels of Si, P, Cl and K and could be related to the concurrent decrease in dissolved organic C and increase in intracellular Al. Correlation and factor analysis of intracellular elemental concentrations showed that statistical elemental associations within Stephanodiscus cells were mainly determined by three factors, with P, Cl, Si and K showing higher loadings on the first, Ca, Mn and S on the second, and Fe, Ca and Al on the third factor. Significant correlations among the elements of the first association may indicate the importance of P (ATP), K (through involvement in P metabolism) and Cl (possibly charge balance) in the active Si uptake during the study period.

The excretion of extracellular polymeric substances (EPS) by an axenic culture of the benthic diatom Cylindrotheca closterium was investigated. Two sequential extraction steps proved to be sufficient to remove the bulk of the EPS present. Soluble EPS was recovered by a simple centrifugation step and represented a fraction that was not or was only loosely associated with diatom cells. For the extraction of bound EPS, different procedures were compared. The best results were obtained using distilled water as extraction solvent (1 h, 30 °C). The sugars that were recovered using this procedure were typically associated with aggregates of diatoms. In addition to the distinct differences in localization of the different types of EPS, their temporal dynamics differed in relation to the light–dark cycle. Soluble EPS were continuously released into the medium at a rate of 1·6 pg cell−1 day−1. In contrast, the production of bound EPS was highly light-dependent. In the dark, this bound EPS rapidly disappeared, probably as the result of its utilization by the diatoms.

Differentiation in temperature responses (survival and growth) was investigated among isolates of two tropical to temperate green algal lineages: the Cladophora vagabunda complex and the C. albida/sericea complex. The results were analysed in relation to published data on 18S rRNA and ITS sequence divergence, which have shown that the overall degree of genetic divergence is similar in the two lineages but that very different patterns of radiation have occurred. In the C. vagabunda complex, the two main clades in the well-resolved phylogenetic tree differed mainly in their tolerance to low temperatures. Within-clade variation was no stronger in the Atlantic/Pacific than in the all-Pacific clade. In the C. albida/sericea complex, six distinctive ITS types indicated early radiation. Although distinctive differences were found between some of these types, the thermal responses of others were very similar, indicating physiological stasis. In both lineages there was evidence for some adaptation to local temperature regimes but phylogenetic constraints were generally more important. Isolates with the same ITS sequences showed similar temperature responses even though collected from different climate zones. Evidence was found for a physiological trade-off between growth at high and at low temperatures in the C. albida/sericea complex, whereas, in the C. vagabunda complex, one clade showed more eurythermal growth responses than the other. In the C. vagabunda complex, which is the ancestral lineage of the C. albida/sericea complex, major differentiation was found in cold tolerance but not in heat tolerance, whereas the reverse pattern was found in the derived C. albida/sericea complex. These findings suggest that an acquisition of cold tolerance preceded the loss of heat tolerance during adaptation to colder climates.

The temperature dependence of UV effects was studied for Arctic and temperate isolates of the red macrophytes Palmaria palmata, Coccotylus truncatus and Phycodrys rubens. The effects of daily repeated artificial ultraviolet B and A radiation (UVBR: 280–320 nm, UVAR: 320–400 nm) treatments were examined for all isolates at 6, 12 and 18 °C by measuring growth, optimal quantum yield of PSII (Fv/Fm) and cyclobutane–pyrimidine dimer (CPD) accumulation. Furthermore, possible ecotypic differences in UV sensitivity between Arctic and temperate isolates were evaluated. Large species-specific differences in UV sensitivity were observed for all parameters: the lower subtidal species C. truncatus and P. rubens were highly sensitive to the UV treatments, whereas P. palmata, which predominantly occurs in the upper subtidal zone, was not affected by these treatments. Only minor differences were found between Arctic and temperate isolates, suggesting that no differences in UV sensitivity have evolved in these species. Relative growth rates were temperature-dependent, whereas species-specific UV effects on growth rates were relatively independent of temperature. In contrast, the species-specific decrease in Fv/Fm and its subsequent recovery were temperature-dependent in all species. UV effects on Fv/Fm were lower at 12 and 18 °C compared with 6 °C. In addition, UV effects on Fv/Fm decreased in the course of the experiment at all temperatures, indicating acclimation to the UV treatments. CPDs accumulated during the experiment in both isolates of P. rubens, whereas CPD concentrations remained low for the other two species. CPD accumulation appeared to be independent of temperature. The results suggest that summer temperatures occurring in temperate regions facilitate repair of UV-induced damage and acclimation to UV radiation in these algae compared with Arctic temperatures. Because the differences in UV effects on Fv/Fm, growth and CPD accumulation were relatively small over a broad range of temperatures, it was concluded that the influence of temperature on UV effects is small in these species.

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.

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.

A new member of Delesseriaceae (Ceramiales, Rhodophyta) is described from Southern Taiwan and the Philippines. On the basis of comparative vegetative and reproductive morphology, and phylogenetic analysis inferred from nuclear-encoded large-subunit ribosomal DNA sequences (LSU rDNA), we conclude that it belongs in the genus Drachiella, tribe Schizoserideae, subfamily Phycodryoideae. The new taxon shares with other Drachiella species the absence of macro- and microscopic veins; diffuse growth by marginal and intercalary meristematic cells; a polystromatic, lobed thallus; abundance of rhizoidal marginal proliferations used for attachment; convoluted plastids in surface cells; abundant secondary pit connections among adjacent vegetative cells; large intercellular spaces between surface cells; procarps confined to the upper side of the thallus, circular in outline, consisting of a supporting cell bearing a strongly curved carpogonial branch and two sterile groups that remain undivided; vertical division of gonimoblast initial from auxiliary cell, and unilateral, monopodial branching of gonimoblasts; and mature cystocarps with a massive candelabrum-like fusion cell of fused gonimoblasts bearing carposporangia in branched chains. It is distinguished from the other members of the genus by thalli that consist of extensive tangled mats of prostrate and overlapping decumbent blades, procarps confined to the upper side of the thallus, and the lack of basal stalks or stipes. Whereas the Schizoserideae is predominantly a Southern Ocean tribe, one of the tribe's four genera, Drachiella, was known only from the eastern Atlantic and Mediterranean. We herein report the first record of the genus for the Indo-Pacific Ocean, and describe Drachiella liaoii, sp. nov., as a fourth species in the genus.

An undescribed marine Pyramimonas, P. australis Andreoli et Moro, sp. nov., forming a bloom in a hole of Terra Nova Bay (Ross Sea, Antarctica) sea ice, was collected, but could not be cultured. Consequently, the description of this new species is based on light and electron microscope observations on samples that were fixed or stored at −80 °C, and its phylogenetic position inferred from nuclear-encoded small-subunit ribosomal DNA (SSU rDNA) and chloroplast-encoded rbcL gene sequences. This is the third Antarctic species described for this genus. The ultrastructure of the cell is consistent with species of the subgenus Trichocystis McFadden, but differs in that it has unique body and cyst scales, and a different encystment procedure. The outermost layer of body scales is formed by flat box scales with peripheral perforations oriented parallel to the four edges and with a further eight central perforations oriented perpendicular to the peripheral ones. Crown scales, which in many other species of the genus form the outermost layer over the entire cell body, were observed in this species in the flagellar pit over the box scales. The flagella are covered by a pentagonal underlayer of scales and by limuloid scales with two subsidiary spines, in addition to the central one. Encystment begins in the flagellate form resulting in a cyst with an irregular wall bearing spine scales. Ultrastructural and molecular data confirm that P. australis belongs to the subgenus Trichocystis.

In order to elucidate the phylogeny and evolutionary history of the Bacillariaceae we conducted a phylogenetic analysis of 42 species (sequences were determined from more than two strains of many of the Pseudo-nitzschia species) based on the first 872 base pairs of nuclear-encoded large subunit (LSU) rDNA, which include some of the most variable domains. Four araphid genera were used as the outgroup in maximum likelihood, parsimony and distance analyses. The phylogenetic inferences revealed the Bacillariaceae as monophyletic (bootstrap support [ges ]90%). A clade comprising Pseudo-nitzschia, Fragilariopsis and Nitzschia americana (clade A) was supported by high bootstrap values ([ges ]94%) and agreed with the morphological features revealed by electron microscopy. Data for 29 taxa indicate a subdivision of clade A, one clade comprising Pseudo-nitzschia species, a second clade consisting of Pseudo-nitzschia species and Nitzschia americana, and a third clade comprising Fragilariopsis species. Pseudo-nitzschia as presently defined is paraphyletic and emendation of the genus is probably needed. The analyses suggested that Nitzschia is not monophyletic, as expected from the great morphological diversity within the genus. A cluster characterized by possession of detailed ornamentation on the frustule is indicated. Eighteen taxa (16 within the Bacillariaceae) were tested for production of domoic acid, a neurotoxic amino acid. Only P. australis, P. multiseries and P. seriata produced domoic acid, and these clustered together in all analyses. Since Nitzschia navis-varingica also produces domoic acid, but is distantly related to the cluster comprising the Pseudo-nitzschia domoic acid producers, it is most parsimonious to suggest that the ability of species in the Bacillariaceae to produce domoic acid has evolved at least twice.

A new diatom (Bacillariophyceae) genus and two new species are described from the arid region of the North American southwest. The new genus, Playaensis, and new species, P. circumfimbria and P. furtiva, are distinguished by frustule morphology and autecology. Playaensis possesses unique, narrowly lunate longitudinal ribs bordering the raphe and spathulate spines, but their evolutionary relationship to known genera is unclear. In Payton Lake, New Mexico, P. circumfimbria and P. furtiva are rare in the diatom community, and their geographic and geological extent are not known, but they may be restricted to alkaline, slightly saline lakes of the region.

This is the first description of a combination coccosphere of the heterococcolithophore species Coronosphaera mediterranea (Lohmann 1902) Gaarder in Gaarder & Heimdal (1977) and the holococcolithophore species Calyptrolithophora hasleana (Gaarder 1962) Heimdal in Heimdal & Gaarder (1980) (Figs 1, 2). A single specimen of this new combination coccosphere was found within 53000 analysed cells in one of 189 samples collected at the JGOFS time series station ALOHA, Hawaii, during 1993 to 1996. The specimen was in a sample collected during autumn 1996 at a water depth of 5 m at a temperature of 26·1 °C, salinity of 35·0 psu, phosphate of 0·002 μmol/kg and in nitrate-depleted water (for details see Cortés, 1998; Cortés et al., 2001).