The development of weighted averaging models for diatoms and lake-water temperature is reviewed in relation to other factors controlling diatom abundance in lakes. It is argued that diatom–temperature models are weaker than those developed for salinity, pH and phosphorus. Moreover, even where a statistically significant model is developed for water temperature, its application over long time periods requires caution. For example, over long time periods (such as the Holocene), soil and vegetation will have changed considerably, altering lake-catchment hydrochemistry and hence the lake biota. Applications of diatom-temperature models in these instances may result in inferred temperatures that are merely artefacts of changing lake-water chemistry. However, palaeolimnological studies using variance partitioning analysis of diatom profiles in sediment cores and independent climate data show that climate signals are recorded in lake sediments. It is suggested, therefore, that the link between changing climate and diatoms be addressed via an alternative method than that of temperature-inference models. The situation demands a more complete understanding of the interactions between lake hydrodynamics and nutrient inputs from catchments over a variety of timescales.

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 chemical composition, biosynthesis and ultrastructural organization of the cell wall of cultures of Koliella antarctica (Klebsormidiales, Chlorophyta), a green microalga obtained from samples of sea water taken near the Italian Station of Terra Nova (Ross Sea) during the austral summer 1989–1990, have been studied. Purified cell walls of the microalga were sequentially treated with chemicals which, in higher plants, solubilize matrix polysaccharides (pectins and hemicelluloses) and leave an insoluble residue considered to be α-cellulose. CDTA plus Na2CO3- and KOH-solubilized polysaccharides were made up of glucosyl residues (more than 90 mol%), as well as some minor sugars (mannose and rhamnose). Linkage analysis and enzymic hydrolysis of the matrix polysaccharides indicated the presence of β-1,4-linked glucans with minor amounts of other uncharacterized polysaccharides. The insoluble residue was composed of a small amount of crystalline α-cellulose associated with mannan or glucomannan chains. The biosynthesis of cell wall polysaccharides was studied by incubating the microalgae in the presence of D-[U-14C]glucose or myo-[U-14C]inositol. The radioactive glycosyl residues incorporated into the polysaccharides solubilized from purified cell walls of the cultured microalga corresponded to those detected in the chemical analysis of the cell wall. The myo-inositol oxidation pathway was demonstrated to be functional in the microalga. Cell wall ultrastructural observations showed a loose network of cellulose microfibrils in an extended matrix.

The first spindle formation in karyogamy-blocked zygotes in the isogamous brown alga Scytosiphon lomentaria was studied by electron and immunofluorescence microscopy using anti-centrin and anti-β-tubulin antibodies. Zygotes blocked in karyogamy by incubation at high temperature (22 °C) were compared with normal zygotes incubated at 14 °C. In normal zygotes, after the disappearance of female gamete centrioles, centrioles from the male gamete duplicated and migrated to both poles in the metaphase, and a bipolar spindle was formed. The nuclear envelope was almost intact except at the poles. In karyogamy-blocked zygotes of S. lomentaria, both DNA synthesis and chromosomal condensation occurred in the male and female nuclei. A bipolar mitotic spindle with a pair of centrioles at each of two poles could be observed in the male nucleus, but not in the female nucleus. In some cases, after a pair of centrioles derived from the male gamete duplicated and separated, one of the two pairs migrated towards the female nucleus. In this case, a monopolar spindle was formed independently in each of the female and male nuclei. In addition to the monopolar spindle, a bipolar spindle was formed lying across the unfused male and female nuclei. Male and female chromosomes were intermixed and some of them were incorporated into the spindle. After cytokinesis of the normal and karyogamy-blocked zygotes, two daughter cells, each with one nucleus and one chloroplast, were formed.

The coenocytic green alga Caulerpa racemosa colonized the Mediterranean some time after the opening of the Suez Canal in 1869. For most of the past century it has remained confined to the southeastern Mediterranean, but over the past several years the species has been reported in abundance along the western coasts of Italy, Sardinia and the Marseille area of southern France. Whether this constitutes a natural range expansion or a possible new introduction is under discussion. The purpose of this study was to establish the ITS signatures of populations inside and outside the Mediterranean. ITS1 sequences were compared among 78 clones from 21 individuals representing 11 populations of C. racemosa, collected from the Western Mediterranean, the Canary Islands, Panama and Western Australia. Intra-individual polymorphism of ITS1 was found to be as high or higher than inter-individual polymorphism across all samples tested. Polymorphism parsimony analysis, which takes into account intra-individual variation, revealed strong separation between individuals from Panama, Fuerteventura (Canary Is.) and the Mediterranean. In contrast, none of the six Mediterranean populations could be distinguished from one another. In addition, individuals and their clones collected from Perth (Australia) and Gran Canaria were spread throughout the Mediterranean clade. Possible reasons for the lack of homogenization of ITS arrays in C. racemosa under the mechanisms of concerted evolution and implications for phylogeographic interpretation are discussed and compared with Caulerpa taxifolia.

Single-stranded conformational polymorphism (SSCP) analysis of Rubisco spacer plastid haplotypes was used to assess population differentiation in the mangrove-dwelling red alga Caloglossa leprieurii (Montagne) J. Agardh. Over 1000 samples from 16 populations in northern and eastern Australia were scored with SSCP. Seven haplotypes were discovered, three of which were only found in single populations. The haplotypes formed three phylogenetically distinct lineages. A haplotype found only in north Australia (haplotype N) has closer affinities with a haplotype previously found in Japan than with any other Australian haplotypes. One haplotype (B) was dominant in northern populations and another (C) was dominant in southern populations. Haplotype A was found in geographically intermediate populations but never in high abundance ([les ] 10%). Population analysis of haplotype frequencies revealed that many populations were significantly differentiated from each other. These data indicate that populations of C. leprieurii in Australia are genetically isolated from each other, as many individual populations, probably due to limited gene flow.

The early life stages of Hormosira banksii can be viewed as a series of distinct developmental events such as gamete release, fertilization, germination, adhesion, cell division, apical hair formation and growth. These developmental stages can be targeted for experimentation as well as used as a measure of health in bioassay tests. Three bioassays were devised and compared to determine which developmental events in H. banksii are most susceptible to effluent (40%) and/or reduced salinity (21‰ S). These treatments approximate conditions in the shore zone where H. banksii once occurred at Boags Rocks, Victoria, Australia. Reduced salinity and sewage effluent affected developing H. banksii differently. Damage caused by reduced salinity occurred within the first 48 h and affected fertilization and germination. Exposure to sewage effluent did not affect fertilization but reduced the number of healthy embryos that had formed a wall by 24 h, germinated by 48 h and divided by 72 h. Both sewage effluent (40%) and reduced salinity (21‰ S) significantly decreased the number of healthy developing embryos that had adhered by 24 and 48 h.

The composition (% relative abundance) of the benthic diatom community was studied in the littoral zone (0–5 m) of the NW and E coasts of the brackish, non-tidal Gulf of Riga, in the Baltic Sea. The samples were collected concomitantly with measurements of sediment primary productivity and chlorophyll a during three cruises, representing three seasons (autumn, spring, summer). At all depths, the living diatom community was dominated by epipsammic species, the most abundant taxa being Martyana atomus, a species of Fragilariaceae and Achnanthes delicatula. The community was characterized by a stable composition and a high species diversity throughout the study period (Shannon–Weaver, mean H′ = 4·4). Principal Component Analyses (PCA), together with Redundancy Analysis (RDA) based on 129 taxa, revealed both spatial (site and depth) and seasonal differences in the diatom communities. However, these differences were mainly caused by the varying proportions of taxa common in both sampling areas in all three seasons, rather than by actual major taxonomic changes in the species present in communities. The distribution of the typical epipsammic species along the depth gradient was not uni-directional. The dominance of attached life forms, and the absence of a well-developed epipelic community, reflects the physically dynamic substratum, particularly in the eastern part of the Gulf. As a result, primary productivity is kept rather low, decreasing rapidly with depth due to frequent turbidity of the water column.

The red algae Chondrophycus patentirameus (Montagne) Nam (‘patentiramea’) and L. paniculata (C. Agardh) J. Agardh were investigated on the basis of type material and recent collections. Both species show the following features: (i) production of two vegetative pericentral cells from each axial segment; (ii) absence of secondary pit connections between cortical cells; (iii) lack of projecting cortical cells near the apex; (iv) absence of lenticular thickenings in the walls of medullary cells; and (v) perpendicular arrangement of tetrasporangia, each of which is produced from the second pericentral cell in each fertile segment with no additional tetrasporangial pericentral cells. However, C. patentirameus has a stoloniferous holdfast, divaricate branching (with branches arising at angles up to 90°) and non-palisade-like superficial cortical cells, whereas L. paniculata has a discoid holdfast, non-divaricate branching and a palisade-like cortical layer. From this study it is concluded that C. patentirameus (here lectotypified) is distinct from L. paniculata. The latter species is here transferred to the genus Chondrophycus (Tokida & Saito) Garbary & T. Harper as follows: Chondrophycus paniculatus (C. Agardh) G. Furnari.

The effect of copper additions (Cu ranging from 0 to 30 μM) on the photosynthesis of three different microalgal biofilms was studied to identify the factors that cause sensitivity differences between benthic and pelagic algae. The response of biofilms which colonized artificial substrata in the River Meuse was compared with those of two laboratory-grown monospecific biofilms, one consisting of the diatom Synedra ulna, and the other composed of a filament-forming cyanobacterium, Oscillatoria sp. The photosynthetic yield ΦII (quantum efficiency of photosystem II) was studied with PAM (Pulse Amplitude Modulated) fluorimetry. S. ulna biofilms appeared to be the most sensitive to Cu, followed by the cyanobacteria, while natural biofilms, dominated by supposedly very sensitive diatom species such as Melosira varians and Diatoma vulgare, were the most resistant to Cu. In the highly productive biofilms, pH is suggested to play a role in lowering toxicity by helping the precipitation of cupric ions. Cu accumulation by the biofilms during the exposure period followed a linear relationship with Cu concentration, saturation not being observed; natural biofilms had an accumulation factor of 1–2·5 × 103 relative to the concentrations in the water, while the diatoms growing unattached to the substratum had a higher concentration factor, up to 4·9 × 103. It was concluded that the physical structure of the biofilm (package of cells and thickness), and not the species composition, was the main factor regulating the sensitivity of the biofilm to Cu toxicity during short-term exposures.