Use of isozymes (including allozymes) in studies of population genetics and systematics of seaweeds has increased sufficiently in the last decade to allow some generalization. Only a single locus has been observed for about half the enzymes analysed in seaweeds, compared with 29% in vascular plants. Compared with higher plants, macroalgal species generally have low amounts of electrophoretically detectable genetic variation; the lowest levels of genetic variation found in natural populations are those reported for seaweeds. Nonetheless, seaweeds show an association between levels of genetic diversity as revealed by isozymes and species-specific attributes, such as mating system and predominance of asexual versus sexual reproduction. In systematic studies, isozymes have revealed cryptic species and identified pairs of sibling taxa. The quaternary structure of enzymes appears to be conserved at the phylum level. With the current availability of improved techniques for enzyme electrophoresis and for data interpretation, we expect future studies utilizing isozyme electrophoresis to provide further insight into population and evolutionary processes in seaweeds.

This paper continues a series of studies of the allogamous raphid diatom Achnanthes longipes, which has a complex reproductive system combining unisexual, bisexual and monoecious behaviour. Following earlier work on the effects of inbreeding in the progeny of crosses between two unisexual clones, we studied the progeny of clones that are capable of a high degree of selfing in monoclonal culture (‘monoecious clones’). Three generations of selfed progeny were examined. In addition, we investigated the F1 generation obtained after crossing two different monoecious clones. Monoecious clones produced monoecious or, more rarely, bisexual progeny, but did not give rise to unisexual progeny. As in inbred lineages made by crossing closely related unisexual clones, inbreeding in monoecious lineages leads to a reduction in the number of gametes formed by the gametangia, from two to one. Inbred clones exhibit marked inbreeding depression and only three inbred generations were possible in monoecious lineages. In the third, final inbred generation, monoecious sexual reproduction was initiated in monoclonal cultures but gametes rarely fused and none of the auxospores and initial cells that were formed were viable; this also occurred when the inbred clones were crossed with any of the other clones available. The significance of inbreeding and other aspects of the breeding system in A. longipes is discussed.

Presidential addresses pose problems. Should one review some area or report a new piece of research; or should one be less predictable? I have chosen the latter, inspired by a BBC radio talk given by Sir Peter Medawar (1964). The talk, ‘Is the scientific paper a fraud?’, introduced a series about how scientific work is really done. Medawar, a biologist and Nobel Laureate, concluded that the scientific paper is a fraud because it misleads the reader, indeed generally lies about the making of scientific discoveries, which are usually presented as well-planned, objective, logical and dispassionate. Scientists, he wrote ‘should not be ashamed to admit, as many of them apparently are ashamed to admit, that hypotheses appear in their minds along uncharted byways of thought; that they are imaginative and inspirational in character; that they are indeed adventures of the mind.’

There followed a series of talks by the likes of Otto Frisch, Edward Bullard, Tom Cottrell and R. V. Jones which amply demonstrated Medawar's conclusions. Finally there was a summary by a historian and philosopher, J. W. N. Watkins (1964), which commented on the conventional style (‘didactic dead-pan’) of scientific papers: ‘if natural scientists … took to writing in a candid, uncensored, autobiographical way, setting out their ideas in their natural order, didactic dead-pan would gradually fall into discredit outside science too. A gratuitous barrier to mutual comprehensibility would have faded away.’ We should heed these words at a time when science has never been so successful in developing understanding of natural phenomena; but a time also when it has abysmally failed to retain public confidence, partly through alienation with its jargon, partly through the arrogance of some of its practitioners, and partly through the suspicion which harnessing of science for exploitative interests naturally brings.

I have a story to tell about how ideas have developed in understanding the role of algae in shallow freshwater ecosystems and I shall tell it in a way that Medawar and Watkins would have approved of. Recently I received a questionnaire asking me which of several things determined what research I do. It had much of the standard terminology of bureaucrat-driven management: Foresight exercise; Competitiveness; Research assessment exercise; Patents; Grant income. It was redolent with the terminology of money, power and influence, none of which have much relevance to the research I do or why I do it. I think that for me, at least, doing research is one way of understanding myself, and my needs, and therefore, possibly, the needs of others. What I do, how I do it, and how I interpret the data are functions of my past experience and of lucky opportunities that have arisen. They have little to do with forward planning and I do not believe that I am unusual in any of this.

Chlamydomyxa labyrinthuloides is a heterokont alga known since the last century. It lives on Sphagnum and other water plants as aplanospores or plasmodia. We have investigated the taxonomic position of Chlamydomyxa labyrinthuloides by combining results from morphological studies, pigment analyses and a molecular phylogenetic analysis of the small subunit (SSU) rRNA gene. Chlamydomyxa labyrinthuloides shares morphological features with xanthophytes and chrysophytes, whereas pigment composition indicates a grouping with the phaeophytes, raphidophytes and chrysophytes. The sequence of the SSU rRNA gene and its phylogenetic reconstruction unambiguously demonstrate that Chlamydomyxa labyrinthuloides is related to the chrysophytes.

Drying of cells leads to damage resulting from crowding of cytoplasmic components, condensation of the nucleoid, increases in the Tm of membrane phase transitions, and imposition of stress upon cell walls. Prolonged desiccation leads to oxidation of proteins, DNA and membrane components through metal-dependent Fenton reactions, while Maillard reactions generate cross-linked products between the carbonyl groups of reducing sugars and the primary amines of nucleic acids and proteins. Although such damage restricts many organisms to aqueous environments, some, including many cyanobacteria, can tolerate the air-dried state for prolonged periods. Cyanobacteria in the Tintenstrich communities of exposed rock faces, Microcoleus and Lyngbya spp. in intertidal mats, chasmoendolithic Chroococcidiopsis spp. in the rocks of hot and cold deserts, and terrestrial epilithic crusts of Tolypothrix and Nostoc are examples that show a marked capacity to withstand the removal of their cellular water. For Nostoc commune, the mechanisms of desiccation tolerance reflect both simple and complex interactions at the structural, physiological and molecular levels.

As a basis for inferring phylogenetic relationships between Pelvetia and Pelvetiopsis in the family Fucaceae, the complete sequences of the plastid-encoded RuBisCo spacer region were determined for all four species of Pelvetia, for the type species of Pelvetiopsis, P. limitata, and for three other fucacean species (Ascophyllum nodosum, Fucus gardneri and F. vesiculosus). All trees based on the sequences of the RuBisCo spacer region showed that Pelvetia is not monophyletic and consists of two clades, one including P. babingtonii, P. compressa, and P. siliquosa, the other comprising only the type species, P. canaliculata. P. canaliculata is not closely related to any of the other Fucaceae studied, and it may represent a monotypic genus. RuBisCo spacer sequences support the establishment of a new genus for the three Pacific Pelvetia species: P. babingtonii, P. compressa and P. siliquosa. The congruence of the RuBisCo spacer data with reported nuclear rDNA 18S and ITS sequences, and with biogeographical and morphological data, indicates that the RuBisCo spacer region, including its flanking areas, is useful for inferring phylogenetic relationships within the Fucaceae.

If the depletion of the stratospheric ozone shield continues, the influx of solar UV-B radiation (280–320 nm) will increase in the near future. In photosynthetic organisms there are several targets for the deleterious UV-B radiation, such as proteins, DNA and membranes. Cyanobacteria use three different types of strategies to counteract UV damage: (i) stress avoidance by gliding mechanisms, (ii) stress defence by synthesis of UV-absorbing compounds, antioxidants and extracellular polysaccharides, and (iii) repair mechanisms including DNA repair and resynthesis of UV-sensitive proteins. In the past, most studies concentrated on the physiological aspects of UV tolerance whereas the molecular basis of UV tolerance in cyanobacteria is poorly understood. We will summarize the effects of and responses to UV-B at the physiological and molecular levels and present data on the influence of UV-B irradiation on the proteome of the terrestrial cyanobacterium Nostoc commune. SDS-PAGE and high-resolution two-dimensional gel electrophoresis were used to analyse the influence of UV-B on the proteome of N. commune. The resolution of SDS-PAGE turned out to be far too low to monitor the UV acclimation process. In contrast to the latter technique, two-dimensional electrophoresis showed that the UV-B response is extremely complex, involving the induction and the repression of a large number of proteins.

The affinity for HCO3− and carbonic anhydrase activity (CA; EC 4.2.1.1) were determined in the red macroalga Bostrychia scorpioides. The affinity for HCO3− was assessed by using three independent methods: the effect of a high pH on photosynthetic rates, photosynthetic conductance for CO2 estimated from the initial slope of photosynthesis rate versus inorganic carbon concentration curves, and the CO2 compensation point. The results obtained from the three methods were consistent in demonstrating that B. scorpioides has a very low affinity for HCO3−, although a certain capacity for its use must not be ruled out. High activities of both external and internal CA were found. Internal CA activity was 10-fold higher than external. External and internal CA were necessary for photosynthesis at pH values higher than 7·0 because O2 evolution was inhibited after adding acetazolamide and ethoxyzolamide (inhibitors of CA). The effect of changing O2 concentration on photosynthesis was also examined. Bostrychia scorpioides exhibited a high sensitivity to O2, demonstrating a C3-like photosynthetic gas exchange physiology. Therefore, the high level of CA activity in B. scorpioides was not enough to support a high affinity for HCO3− and to prevent photorespiration.

Haslea ostrearia, the peculiar diatom that develops in oyster-ponds and synthesizes a water-soluble blue pigment (marennine), was grown in a semi-continuous mode over a wide range of irradiances (20–750 μmol; m−2 s−1). Growth, photosynthesis and pigment content were determined for algae maintained in exponential growth phase by regular dilution with fresh medium. Increasing the growth irradiance resulted in a decrease in the chloroplast length, but had no clear influence on the size of the cellular compartments pigmented by marennine accumulation. Growth rates increased with irradiance from 20 to 100 μmol; m−2 s−1 and were constant from 100 to 750 μmol; m−2 s−1. Increasing growth irradiance caused a decrease in the cellular content of chlorophylls a and c and fucoxanthin, in contrast to diadinoxanthin. Algae acclimated to high irradiance had lower maximum photosynthetic rate (Pnm) and maximum light utilization coefficient (α) when expressed on a per cell basis. On a chlorophyll a basis, the higher the growth irradiance, the lower the maximum light utilization coefficient and the higher the maximum photosynthetic rate. No photoinhibition was observed at irradiances up to 1500 μmol; m−2 s−1 whatever the growth irradiance. In vivo chlorophyll a fluorescence showed that cells grown at high irradiance had effective photosystem II quantum efficiency (measured at the growth irradiance) considerably lower than that of cells grown at low irradiance. Thus H. ostrearia withstands high light exposure, consistent with the observation that this alga can outcompete other diatoms encountered in oyster-ponds characterized by low turbidity and shallow depth.

Free-floating Ulva L. biomass in the eutrophic brackish ‘Veerse Meer’ lagoon (southwest Netherlands) consists of four morphologically identified species: U. curvata (Kützing) De Toni, U. lactuca L., U. rigida C. Agardh and U. scandinavica Bliding. U. curvata could be recognized easily because of the characteristic central cavity in the holdfast of the attached plants, the arrangement of cells in rows and the single pyrenoid in each cell. U. rigida was distinguished by the thick thallus and the large number of pyrenoids. The Veerse Meer isolate, however, was slightly different from the isolate from the Oosterschelde estuary (the Netherlands). U. lactuca and U. scandinavica showed a high degree of overlap in thallus thickness and cell size, but U. scandinavica usually possessed more pyrenoids. However, doubts have frequently been expressed about the use of some morphological characters in Ulva taxonomy. To determine the validity of such characters in the identification of Ulva species, the morphological variation within and between morphological species was recorded and a molecular data set generated. To detect possible ecophysiological differences between species, optimum temperatures and salinities for growth were determined experimentally. The sequences of the nuclear ribosomal DNA internal transcribed spacer 2 (ITS2) and flanking regions of U. lactuca, U. rigida and U. scandinavica from the Veerse Meer were all identical, but differed from that of U. rigida from the Oosterschelde estuary. Ulva species from the Veerse Meer were most closely related to U. armoricana and U. rigida from Brittany (2·9% and 3·5% divergence respectively); the difference between U. rigida from the Veerse Meer and from the Oosterschelde estuary was 7·5%. Rooted trees, based on a comparison of these sequences with sequences of other Ulva and Enteromorpha species obtained from the literature, using Monostroma arcticum as outgroup, suggested that Ulva is paraphyletic with respect to Enteromorpha. The optimum temperature for growth of U. curvata was 25 °C; for all other species it was 10 °C. The optimum salinity for growth was 30 °C for all isolates. It is concluded that U. lactuca, U rigida and U. scandinavica from the Veerse Meer are all members of one highly polymorphic species.

Vegetative and reproductive growth of individually marked plants of the brown alga Himanthalia elongata was monitored over 2·5 years at two sites with different wave exposures on the Irish west coast. Macro-recruits were first visible to the unaided eye in February/March. About 65% of all buttons produced receptacles during autumn of the same year, whereas others remained sterile. Growth of receptacles started between late August and late November, when vegetative plants were 9–14 months old, but no further plants became reproductive after December. At both sites, length increase of receptacles was greatest between February and April, but only longitudinal growth occurred and no more new dichotomies were produced. At the more wave-exposed site, growth was fastest in plants growing in red algal turfs and slowest in plants on open rock. Growth rates were maximal when seawater temperatures were 10–12 °C in early spring but decreased from May onwards with the maturation of receptacles aged 7–9 months in June. Release of viable gametes started in June and continued throughout the autumn and winter, until all plants disappeared from the population in February. Plant density was highest in March after the appearance of macro-recruits in the population, and declined during summer when the number of buttons decreased. Percentage plant cover was highest in June immediately before the onset of gamete release and this was followed by the decay and disintegration of receptacles. Since both survival and growth of young buttons was highest in red algal turfs and lowest on exposed rocks, the distribution of H. elongata on semi-exposed shores in Ireland may be limited by the availability of suitable micro-habitats for recruitment, and reduced by the early loss of fertile, adult plants from exposed sites.

The cyanobacterial fossil record is among the oldest for any group of organisms, possibly reaching back to 3500 Ma ago. The molecular phylogeny of cyanobacteria is complementary to the fossil findings, confirming the antiquity of the group, the role of cyanobacteria in the evolution of planetary primary production, and the symbiotic origins of plastids in algae and plants from cyanobacterial ancestors. The study of fossil cyanobacteria followed the discovery of Precambrian microbial fossils by S.A Tyler and E.S. Barghoorn in 1954, and is still developing. Most fossil cyanobacteria are preserved in permineralized conditions in cherts and phosphorites or as organic compressions in shales. The interpretation of fossil cyanobacteria is aided by the study of modern counterparts, preferably within their natural habitats. These comparisons include the post mortem degradation of cellular remains. The fortuitous preservation and fossilization of ancient cyanobacterial communities in growth position, i.e. in the synsedimentary context, allows one to draw conclusions about their palaeoenvironment, including interactions between cyanobacteria and ancient sediments. These relations are based on cyanobacterial ecological requirements, and they compare well with behavioural responses of modern cyanobacteria in microbial mats and modern stromatolites. The general trend in the evolution of cyanobacteria is one of gradually increasing complexity and diversity, but the group shows a conservative maintenance of morphological adaptations to successful ecological niches. Accordingly, a large proportion of ancient morphological types is still represented among modern cyanobacteria. Fossil to Recent counterparts are identified for several coccoid and filamentous cyanobacteria. Evidence for heterocystous cyanobacteria is indirect, through identification of fossil akinetes.

The nucleotides and nucleoside diphosphate monosaccharides (NDP-sugars), UDP-galactose, UDP-glucose, UDP, ATP, ADP, ADP-glucose, AMP and NAD, some of which are involved in carrageenan biosynthesis, were identified in the two carrageenophytes Calliblepharis jubata and Solieria chordalis and quantified by high-performance liquid chromatography (HPLC). Of several extraction procedures evaluated, a freeze-thaw step followed by formic acid (1 M) extraction was the preferred method. The pool size of nucleotides and NDP-sugars differed between the two algal species, which may be related to their growth state. Calliblepharis, which was not growing actively, had larger pools than Solieria, which was in an active growth phase. Using an HPLC method UDP-D-glucose-4-epimerase activity was measured in cell-free extracts of both algae, for the first time in a carrageenophyte.

The ultrastructural changes taking place in Dunaliella bioculata after chronic exposure to a sodium chloride-induced stress were examined. Hyperosmotic shock was induced by raising the sodium chloride concentration of the culture medium from 0·3 to 1·3 M, which affected a number of cellular organelles during the initial stages of the stress period, i.e. 24, 48 and 72 h. Changes in whole-cell volume were recorded, as well as alterations in the size of the following components: starch grains and sheath, lipid and plastoglobuli, chloroplast, pyrenoid, nucleus, mitochondria, cytoplasm, Golgi apparatus and endoplasmic reticulum. Cells were examined using transmission electron microscopy and changes to their fine structure quantified via image analysis of the electron micrographs. The image analysis program was designed to measure various geometric parameters for all the cell components within individual algal cells. Quantitative image analysis of cells subjected to a chronic salt stress revealed marked increases in the cross-sectional areas of the Golgi apparatus and the endoplasmic reticulum. The enhanced production of the Golgi apparatus within the algal cells was thought to be the direct result of a salt-stress-induced endoplasmic reticulum production within the cells. The increase in the endoplasmic reticulum was manifested as extensive networks of cortical endoplasmic reticulum. It is suggested that the endoplasmic reticulum serves both physiological and structural roles during chronic salt stress by providing the driving force behind increased synthetic/Golgi apparatus activities of the cells, and by providing a type of ‘cellular scaffolding’ to limit the degree of cell contraction in the face of long-term salt stress.

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.

Immunofluorescence assays using polyclonal and preadsorbed antibodies as well as FITC-labelled lectins were employed to characterize two morphospecies of the cyanophytes Pseudanabaena catenata and P. planctonica from laboratory cultures isolated from two reservoirs in Spain and one in Denmark. Binding of both antibodies and lectins was unaffected by phase of the cell division cycle, growth phase and environmental factors such as culture medium, light or temperature. Good-quality polyclonal antibodies were obtained for several strains of both morphospecies. As expected, different morphospecies from the same location do not share common antigens while strains of the same morphospecies grown in different reservoirs do share most of their surface antigens. However, P. catenata grown at La Pinilla (Spain) does not share common antigens with P. catenata from Bastrup (Denmark). Geographical barriers, in this case, seem to play an important role in determining surface antigen diversity. Similar results are obtained when lectins are used, and some lectins are found to be useful tools for differentiating clones of the same morphospecies. From a genetic point of view there may be no clear species boundary for some morphospecies of cyanobacteria. A ‘fuzzy species’ concept, i.e. a species that belongs in part to more than one species or has characteristics of more than one species, is speculatively considered to explain genospecies boundaries of cyanobacteria.

Nostoc caeruleum, N. commune, N. microscopicum, N. parmelioides, N. pruniforme, N. verrucosum and N. zetterstedtii are all cyanobacteria forming macroscopically visible colonies. They were selected for a nature conservation case study. Their specific identity is easily determined, and reliable historical records are available. Life conditions for these species in Europe in the ‘virgin’ postglacial biosphere, historical reports and the present-day situation are surveyed. Data concerning type materials, supplements to the protologues, and morphology are presented. The classic descriptions and diagnoses based only on herbarium material are supplemented by ontogenetic details. Global/regional changes in the biosphere (climate, regulation of lake levels and river flows, import of plant nutrients, water pollution, acidification, etc.) and their consequences for aquatic biocoenoses are reviewed. The analysis of man-made impacts on the environment enables us to evaluate the present state of habitats where these algae occur today or where they are now extinct. Documented changes in environmental conditions in the past serve as a basis for assessing the likely future developments of the biotopes and of the whole landscape where these cyanobacteria form part of the biocoenoses. However, there are few recent detailed ecological studies on benthic and terrestrial cyanobacteria. It is not yet clear which of the different components covered by the comprehensive term ‘eutrophication’ is the decisive factor for the changes in aquatic biocoenoses and the decline of cyanobacterial biodiversity.

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.

Phenolic compounds, packaged within vesicles known as physodes, are a major cytoplasmic constituent of eggs and zygotes of the Australasian fucoid Hormosira banksii. Physode movement in early life stages of Hormosira is described. We have used the cytoskeletal inhibitors cytochalasin B, latrunculin B and nocodazole added during different stages of development to investigate the role of the cytoskeleton in movement of these vesicles to regions of active wall formation in the growing rhizoid tip and the plane of cytokinesis prior to cell division. Actin inhibition prevented polarization, cross-wall formation and physode movement. When microtubules were disrupted polarization was still possible, but cross-wall formation and physode movement were prevented. Both actin microfilaments and microtubules are necessary to move physodes to regions of accumulation and active wall formation.

Effects of irradiance and temperature on the Mediterranean red algae Eupogodon spinellus and Eupogodon planus were tested. Growth of both species was saturated at an irradiance of 10–20 μmol m−2 s−1, which is in accordance with their sublittoral habitat. Eupogodon spinellus and E. planus survived permanently at temperatures between 8 and 30 °C. The temperature optimum for growth was 25 °C with suboptimal growth occurring at (10−)15 and 30 °C in both species. At their collection locality (Corsica), potential monthly growth yields would be highest in summer and in winter would be only about 20% of the maximum. Reproductive requirements could be determined only in E. planus. Gametophytes reproduced both in long and in short days but only at 20 °C. Tetrasporophytes reproduced at 15–20 °C but only in short days. Geographic distribution boundaries are not set by growth or survival limits. However, the reproductive requirements of E. planus did account for its restricted distribution in the Mediterranean and on the Canary Islands.