Single coccoliths of Emiliania huxleyi grown in mesocosm enclosures (60°16′N, 05°14′E, May–June 1991) under different N[ratio ]P regimes were analysed in a scanning electron microscope. The results indicate that only E. huxleyi with Type A coccoliths was present in the enclosures. Approximately 80–90% of the total coccolith assemblages had developed normally, whilst the remainder were malformed, incompletely grown or dissolved. Severely under-calcified specimens were rare and dissolution and breakage less than 5%. The coccoliths were of larger size than normal, as has been found previously in fjords of southwestern Norway, supporting the conclusion that a local population of E. huxleyi has developed, specific to these waters. Both phosphorus and nitrogen stress caused significant changes in coccolith size and evidence of malformation was clear, particularly in the low-phosphate enclosure. Although the observations presented here concern only Type A coccoliths and it is not known how nutrient stress may affect the coccoliths of the other types of E. huxleyi, they do serve to stress the fact that environmental conditions may possibly obscure genetically determined features. Following our observations on coccolith morphology in relation to nutrient status in enclosures, it will be of interest to test whether a similar correlation can be detected in the natural environment.

In this study we tested the hypothesis that iron limitation suppresses photoacclimation in cultures of the Antarctic flagellate Pyramimonas sp. The cultures were exposed to two different irradiances under iron-rich and iron-poor conditions. Light-harvesting capacity was determined by assessing the pigment composition and measuring in vivo absorption spectra. Light utilization efficiency (α) was determined from photosynthesis versus irradiance curves. The quantum yield of photosynthesis (ϕm) was calculated using α and the absorption spectra. Iron limitation led to commonly observed changes in cells of Pyramimonas, that is, a decrease in cellular pigment content and a reduction in cellular carbon and nitrogen quota. A reduction in αcell followed a decrease in ϕm and light-harvesting capacity. Interpretation of the effects of iron limitation was different when considered on a carbon basis. Because iron limitation resulted in a decrease in cellular carbon content, the carbon-specific absorption coefficient was not affected. Consequently, the observed decrease in αC was mainly due to the decrease in ϕm, showing that iron limitation did not control light utilization via pigment synthesis but exerted control on energy transfer. This is supported by the findings that at high irradiance a shift in pigment ratios within the total pool of violaxanthin, antheraxanthin and zeaxanthin towards zeaxanthin, which is indicative of photoacclimation to high irradiance, was observed for iron-replete cells as well as for iron-depleted cells. In contrast to what is generally hypothesized, the effects of iron limitation were not enhanced at low irradiance. Low irradiance led to an increase in the cellular light-harvesting pigment content. This increase was less pronounced in iron-depleted cells than in iron-replete cells. However, looking at the light-harvesting capacity of the cells on a carbon basis, it was found that iron-depleted cells responded similarly to iron-replete cells. We therefore conclude that the light-harvesting capacity was governed by light conditions and not by iron limitation. In addition to the increase in absorption capacity at low irradiance, an increase in light utilization efficiency was measured, again under both iron-rich and iron-poor conditions. Notably, the relative increase in αC was strongest in iron-depleted cells. Photoacclimation was clearly demonstrated by normalizing α to chl a. For iron-replete cells, αchl was highest at high irradiance. In contrast, for iron-depleted cells αchl was highest at low irradiance. We argue that iron-depleted cells can photoacclimate to low irradiance by a reduction in the ‘package effect’ and reducing growth rates.

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.

Twenty-one marine and freshwater specimens of Hildenbrandia from Europe were compared by analyses of morphometric data and sequences of the rbcL chloroplast gene (which codes for the large subunit of the ribulose-1,5-bisphosphate carboxylase/oxygenase enzyme) and the nuclear 18S ribosomal RNA (rRNA) gene. Eleven freshwater specimens, all corresponding to H. rivularis, were collected from the British Isles, Germany, France, Austria, Spain and Italy. Six marine specimens, representing H. rubra, were obtained from Northern Ireland, Wales, France, Norway, Sweden and the Netherlands, while four marine specimens, corresponding to H. crouanii, were collected from Scotland and Germany. Morphometric analyses of vegetative and reproductive characters distinguished three groups of specimens, which correspond to the three species. Parsimony and distance analyses of the rbcL and 18S rRNA genes were performed on these samples and sequences of North American representatives were included to determine their inter-relationships. The rbcL gene sequence analyses separated the marine and freshwater specimens, with the H. rivularis and H. angolensis representatives forming a well- supported monophyletic clade. The rbcL sequence analyses did not resolve the groupings of marine specimens determined in the morphometric analysis. Analyses of the 18S rRNA gene sequences also supported separation of the marine samples from freshwater samples, although the bootstrap and decay support was not as strong as for the rbcL gene. H. rubra formed a monophyletic clade that was weakly supported. In terms of biogeographic trends, the fairly low intraspecific divergence of H. rivularis (0–1·9% for the rbcL gene and 0–3·6% for the 18S rRNA gene) and the positioning of these samples in the gene trees supports the concept that they are derived from marine populations.

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 ultrastructure of male gametes of Ectocarpus siliculosus is described and discussed in relation to the information available on other brown algal zoids. In general, the fine structure and the organelle associations agree with those of other brown algal cells. In particular, the male gametes typically contain a single chloroplast with a pyrenoid and a prominent concave eyespot, into which the swelling of the posterior flagellum (the photoreceptor) fits. The continuity of the chloroplast endoplasmic reticulum and nuclear membrane, as well as the presence of a perinuclear Golgi consisting of several dictyosomes, is shown. The fine structure of microbodies, lipid bodies and different types of vesicles, including physodes and coated vesicles, is also discussed. Several specializations of cellular elements and their interactions are unique and have not been reported before. These features include the connection between the nuclear envelope, the Golgi and the flagellar bases mediated by fibres resembling intermediate filaments, and the organization of the Golgi as well as the association of mitochondria and a microtubular flagellar root.

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).

Adenocystis and Utriculidium share many morphological characters. They both possess a hollow, bladder-like thallus, made of a solid cortex and a fluid-filled medulla penetrated by a network of longitudinal filaments, a trichothallic apical meristem responsible for their multiaxial structure, and cryptostomata. There are two somatic phases in their life history: a haplostichous macrothallus and a polystichous microthallus. However, Adenocystis has unilocular sporangia associated with unicellular paraphyses resembling those of the Laminariales, whereas Utriculidium has plurilocular sporangia resembling those of the Scytosiphonales. Adenocystis has been classified either in the Laminariales or in different families of the Ectocarpales sensu lato, or suggested to be close to the Scytothamnales. Utriculidium has also been classified in different groups within the Ectocarpales sensu lato, depending on the authors. The two genera were either considered as closely related and even to be phases of the same complex life history, or placed in separate orders. The life histories obtained in culture have suggested that Adenocystis and Utriculidium are independent taxa. The taxonomic positions of the two genera Adenocystis and Utriculidium, which are currently unresolved, were explored in the present study, using phylogenetic analysis of combined partial LSU and SSU rDNA sequences. A data set of 20 species included Chorda, Chordaria, Dictyosiphon, Laminaria, Punctaria, Scytosiphon and Scytothamnus, the type genera of the families in which Adenocystis and/or Utriculidium were sometimes previously placed. Adenocystis and Utriculidium grouped together in all analyses within Ectocarpales sensu lato but failed to group with the ectocarpalean genera Chordaria, Dictyosiphon, Punctaria or Scytosiphon, as previously hypothesized. In fact they did not show any clear affinity with any other ectocarpalean taxa. On the basis of this result, and morphological data, we propose a new family, Adenocystaceae, to include these two genera. It is hypothesized that their current life cycles derive from an ancestral isomorphic life cycle.

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.

A new method of releasing cellular soluble organic matter from microalgae is reported. This method, which could be used to help characterize the production and taxonomic composition of a phytoplankton bloom, was developed in the laboratory to determine the transition temperature, Tm, for planktonic algae. The Tm of these algae is defined as the temperature at which half the cellular soluble carbon is found extracellularly under standard conditions, by analogy with the definition of Tm in bacteriology. Values of Tm in the range of 23–46·5 °C are reported for six species of Bacillariophyceae (diatoms) and two species of Prymnesiophyceae. Species-specific Tm values are highly reproducible and are regarded as an intrinsic property of the species and its physiological races. Possible field uses of the method are discussed.

In continuing studies on the taxonomy of non-geniculate, coralline algae from South Africa, stipes of the kelp, Ecklonia maxima, in the subtidal zone of Western Cape Province, were frequently observed to be covered with rosy-pink encrusting coralline algae. The reproductive morphology and anatomy of these plants show that they belong to the subfamily Melobesioideae and the genus Synarthrophyton. The specimens agree closely with the holotype of Lithothamnion capense f. eckloniae described by Foslie on the basis of South African material. Synarthrophyton eckloniae is described in detail; the species appears to be endemic to Western Cape Province. Another crustose coralline alga from the subtidal zone of South Africa was found to be conspecific with a syntype of Lithothamnion magellanicum and the lectotype and isolectotype of Lithothamnion muelleri f. neglecta. These are now shown to conform to the generic concept of Synarthrophyton on the basis of their concordance with the characters of that genus. South African material of S. magellanicum is compared with the type specimen of Lithophyllum schmitzii with which it had been synonymized and it is concluded that the two species are distinct. It can be distinguished from type specimens of Lithothamnion lamellatum and L. chatamense, with which previous authors had suggested it might be conspecific, on the basis of anatomical characters, despite similarity in habit. The last two species have not been recorded in South Africa.

A minute parasite of Neosiphonia poko (Hollenberg) Abbott from a shallow lagoon on the central-Pacific Johnston Atoll is described as Neotenophycus ichthyosteus Kraft et Abbott, gen. et sp. nov. The infective parasite cell first connects to a central-axial cell of the host, then emerges from between host pericentral cells at a node before dividing into a three- or four-celled primary axis. Epibasal cells of the parasite divide to form three pericentral cells whose derivatives produce a globular head on the basal cell and on which reproductive structures differentiate almost immediately. Trichoblasts on any life-history stage are completely lacking. Spermatangia are borne on mother cells across the whole thallus surface. Procarps consist of four pericentral cells that encircle a subapical fertile-axial cell in an ampullar configuration, one of the pericentral cells serving as the supporting cell and bearing a four-celled carpogonial branch and a single sterile cell. Diploidization results in a longitudinal/concave division of the auxiliary cell and formation of an arching linear series of inner gonimoblast cells, each dividing toward the thallus surface into gonimoblast filaments of very narrow, horizontally aligned cells terminated by initially monopodial, later by sympodial, carposporangia, the whole of the mature female gametophyte consisting of an amalgam of several cystocarps within a lax jacket of sterile gametophytic tissue. Tetrasporophytes are composed of lobes of pericentral-cell-derived filaments, each axial cell of which is ringed by three pericentral cells producing tetrahedral tetrasporangia enclosed by two pre-sporangial cover cells. Affinities of the new genus are discussed and comparison is made particularly to the enigmatic parasite Episporium centroceratis Möbius. It is concluded that relationships with any previously described tribe are so remote or obscure that the new tribe Neotenophyceae should be proposed for it.

The allogamous raphid diatom Achnanthes longipes C. A. Agardh possesses a complex breeding system involving interactions between three types of clone: monoecious, unisexual and bisexual. Previous studies showed that these three types can be crossed with each other, with a tendency for sexual characteristics to be inherited: inbred monoecious lineages gave rise to monoecious or, very rarely, to bisexual clones, while inbred unisexual lineages yielded unisexual and bisexual clones. The current paper reports on the progeny of crosses between monoecious and unisexual clones and their inbred offspring. All three types of clone appeared in the F1 and F2, although unisexual clones of opposite sex to the parental clone were not found. Inbreeding depression was observed and also a tendency for ‘normal’ auxosporulation (producing two auxospores per pair of gametangia) to be replaced by ‘reduced’ or ‘intermediate’ auxosporulation (producing one auxospore per pair). In addition, patterns of incompatibility were observed that were not seen during earlier studies of clones isolated directly from nature. These included the inability of some F1 clones to mate with each other, in spite of compatibility with all other clones examined (unisexual, bisexual and monoecious).

The physiological adaptation of the phosphate uptake behaviour of the cyanobacterium Anacystis nidulans (Synechococcus leopoliensis) has been studied under phosphate-deficient conditions. We show that, during additions of pulses of phosphate, the individual cells of a population potentially develop a coherent behaviour with respect to the kinetic and energetic properties of the high-affinity phosphate uptake system. These adaptive responses are independent of the amount of stored phosphate and the absolute external phosphate concentration, but depend on the exposure time to elevated phosphate concentrations. We demonstrate that the response to additions of pulses of phosphate triggers further metabolic alterations to CO2 fixation, and the flow of fixed carbon into the pool of low-molecular weight-compounds or glycogen. These alterations may also affect subsequent growth. The ecological relevance of the adaptive phosphate uptake behaviour is discussed with respect to the establishment and stability of natural communities.

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.

Gelidium maggsiae sp. nov. is described from plants found in shallow subtidal maërl beds off the west coast of Ireland, where it attaches to detached coralline algae by peg-like rhizoids. Rhizines are more abundant in the medullary region than in the cortex and erect axes display a prominent central row formed by the axial and periaxial filaments. Gametophytes are bisexual and protandrous and were found only in culture. Post-fertilization and cystocarp development are similar to that of G. pteridifolium and cystocarps are biloculate. Tetrasporophytes are morphologically similar to gametophytes; tetrasporangia are irregularly arranged in pod-shaped terminally inserted stichidia, borne on erect axes and arranged unilaterally. Gametangial plants reproduced under short-day (8[ratio ]16 h) conditions at 20–25°C in enriched media, but gametangial formation was independent of photoperiod when plants were kept in unenriched medium. No tetrasporophytic plants were produced from germinated carpospores, but plants originally collected in a vegetative state formed tetraspongia at 20°C, 16[ratio ]8 h. The validity of several characters previously used in species delimitation within the Gelidiales is discussed, and only cystocarp structure and the bisexual nature of the gametophyte are considered to be reliable characters.

The polarized apical cells of Sphacelaria rigidula display a well-organized cortical F-actin cytoskeleton. This consists of bundles of actin filaments (AFs), assuming definite patterns of organization in different regions of the cell cortex. At the tip region of the apical dome the AFs appear randomly oriented, showing a diffuse fluorescence. Immediately below, at the base of the apical hemisphere, the AFs form a ring-like band around the plasmalemma transverse to the polar cell axis. The rest of the cell cortex is traversed by AFs showing an axial or slightly inclined or helical orientation. Examination of the apical cells of S. rigidula in appropriate thin sections revealed that the wall has a multi-layered structure. In the tip region of the apical dome the cell wall bears randomly oriented cellulose microfibrils (MFs), while in the basal part of the apical dome it is reinforced by a layer of densely arranged transverse MFs. As the cell grows at the apex, the transverse MFs are continuously displaced towards the cell base. Below the transverse MF layer, an additional layer with axial or slightly oblique MFs starts being depositing internally, on the tubular part of the cell. Externally to them, the layer of transversely oriented MFs remains visible. The above observations were confirmed in apical cells of S. tribuloides. MF orientation in the innermost wall layer of the apical cells coincides with that of the cortical AFs observed by fluorescence. This mutual alignment between AFs and MFs in a cell that lacks cortical microtubules (MTs) suggests that the AFs are involved in the oriented deposition of MFs. Experimental disruption of AFs with cytochalasin B caused abnormal MF deposition, a fact strongly supporting the above hypothesis. The transverse MFs forming at the base of the apical dome define the diameter and consequently the cylindrical shape of the apical cells. It is suggested that in the brown algal cells examined the AFs play a morphogenetic role similar to that of cortical microtubules in higher plant cells.

Phylogenetic relationships within the Sphacelariales sensu stricto were investigated using both a molecular and a morphological approach. Twenty species were included, representing all three families (i.e. Cladostephaceae, Sphacelariaceae and Stypocaulaceae) and six of the eight genera. The outgroup consisted of six species representing the Syringodermatales, Dictyotales, Choristocarpaceae and Onslowiaceae. DNA sequences of partial rbcL [1255–1375 nucleotides (nt)] and the adjacent RUBISCO spacer (40–842 nt) were determined in order to assess the molecular phylogeny. Only the 3′-end of the spacer (112 nt positions) was alignable for the ingroup taxa. Partition homogeneity testing showed that rbcL and RUBISCO spacer sequences could be combined. However, analysis of rbcL alone or in combination with the RUBISCO spacer gave the same results with only slight differences in support (bootstrap, jackknife, decay). Support was low at the base of the ingroup. Four basal clades could be discerned: (1) Stypocaulaceae, (2) Sphacelaria radicans, (3) Sphacelaria caespitula and (4) all other included taxa: (Sphacella subtilissima+the Sphacelaria subgenus Propagulifera) and (Cladostephus spongiosus+Sphacelaria nana+the Sphacelaria subgenera Battersia+Pseudochaetopteris). The independent morphological analysis (using 23 unordered morphological characters) revealed high homoplasy and an almost completely unresolved tree in which only the subgenus Propagulifera was supported. The morphological characters were subsequently mapped onto the rbcL tree in order to identify diagnostic or phylogenetically informative characters. Blackening in response to bleach and the presence of secondary segments were found to be basal synapomorphies for the Sphacelariales; presence of propagules with a lenticular central apical cell defines the Propagulifera; and strict acroblastic branching mode and axillary zoidangia define the Stypocaulaceae. The remaining characters have been gained or lost multiple times. This study highlights the problem of extreme morphological convergence and/or plasticity. Four options for a new circumscription including nomenclatural changes are discussed. It is concluded that none of the options will lead to greater clarity with respect to either identification or classification.

The marine red alga known as Laurencia obtusa var. snackeyi (Weber–van Bosse) Yamada (Rhodomelaceae, Ceramiales) is characterized as follows: (1) production of 4 periaxial cells from each axial cell; (2) a few, percurrent, terete, thick main axes arising from a single discoid holdfast without stolon-like branches; (3) alternate-spiral branching; (4) presence of longitudinally oriented secondary pit-connections between contiguous superficial cortical cells; (5) absence of a palisade-like layer; (6) absence of projecting superficial cortical cells; (7) absence of lenticular thickenings in the walls of medullary cells; (8) parallel arrangement of tetrasporangia; and (9) presence of one corps en cerise per superficial cortical cell and trichoblast cell. It differs from L. obtusa (Hudson) Lamouroux in the absence of stolon-like branches with secondary attachment discs and the presence of thicker axes. The following binomial is proposed: Laurencia snackeyi (Weber–van Bosse) Masuda, stat. nov. Halogenated secondary metabolites of this species were investigated for samples from Vietnam and Malaysia. The major metabolites of the Vietnamese sample are palisadin A and aplysistatin, both sesquiterpenoids, whereas the Malaysian samples contain these compounds along with another monocyclofarnesol-derived sesquiterpenoid, 5-acetoxypalisadin B. L. snackeyi is also characterized by this set of secondary metabolites.

Four populations of the newly described freshwater red algal species Batrachospermum spermatoinvolucrum were sampled from British Columbia on the west coast of North America and Labrador on the east. The rDNA internal transcribed spacer (ITS) 1 and 2 sequences, RUBISCO large subunit (rbcL) gene data for three of the populations and morphometric characteristics were compared with those of B. gelatinosum. In addition, the key feature distinguishing B. spermatoinvolucrum, spermatangia on the involucral filaments of the carpogonial branch, was investigated seasonally in one British Columbia population of this species. The ITS analysis suggested that the B. spermatoinvolucrum populations were more closely related to particular B. gelatinosum populations than to each other and did not form a monophyletic clade. Two populations of B. spermatoinvolucrum from Labrador and British Columbia had identical rbcL sequences that were distinct from that of B. gelatinosum. However, the rbcL sequence from the third population of B. spermatoinvolucrum differed by only one nucleotide substitution from the B. gelatinosum populations. The tree generated from the morphometric data showed two groupings, each containing populations of both taxa. The presence of spermatangia-bearing involucral filaments was a stable character throughout the year. On the basis of these findings, B. spermatoinvolucrum is reduced to a form of B. gelatinosum. This form would encompass variant populations with characteristic carpogonial involucral filaments bearing spermatangia.