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.

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.

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.

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.

Based on light and electron microscopical investigations, a new genus Craspedostauros is described for a group of marine biraphid diatoms previously placed in Stauroneis Ehrenberg. The genus Stauronella Mereschkowsky had been erected for one of these species, Amphiprora constricta sensu W. Smith, but Mereschkowsky's name cannot be used for nomenclatural reasons. Craspedostauros species can be recognized by the possession of cribrate areolae, a stauros that is usually narrower than the fascia, many girdle bands with double rows of cribrate areolae and two chloroplasts, fore and aft of the central cytoplasm, each with a central pyrenoid. The genus shows similarities in its pore structure and chloroplast type and arrangement to Mastogloia Thwaites ex W. Smith and Aneumastus Mann & Stickle, suggesting that it is more closely related to these than to other naviculoid genera with a stauros, i.e. Stauroneis, Staurophora Mereschkowsky, Meuniera Silva and Haslea Simonsen. The stauros is a feature that probably arose a number of times. A description of the genus and its currently recognized members is given, with a key to their identification. Four new species are described, the types of which have been deposited in the Natural History Museum, London. The status of Stauronella constricta var. linearis Mereschkowsky remains unclear in the absence of any material from the Black Sea. Some marine stauroneid diatoms that do not belong in Craspedostauros are briefly discussed.

A microalga was isolated from the pack-ice of Wood Bay (Antarctica) during austral summer 1993–4. By comparison with an authentic strain obtained from Sammlung von Algenkulturen at the University of Göttingen (SAG 860–3), its ultrastructural details and pigment composition were very similar to those of Pleurochloris meiringensis. However, sequence analysis of the entire 18S rRNA gene revealed substantial genetic divergence (57 nucleotide substitutions and 19 insertions/deletions) between SAG 860–3 and the Antarctic isolate. Phylogenetic analysis of complete 18S rRNA gene sequences from 18 microalgal species, including the two strains studied, rejected the hypothesis that the Antarctic isolate is the sister species to Pleurochloris meiringensis. Molecular evidence indicates that the Antarctic isolate is the sister group of a clade that comprises two other representatives of the Xanthophyceae (synonym Tribophyceae): Pleurochloris meiringensis and Botrydiopsis intercedens. This leads us to conclude that this microalga is a new species belonging to a new genus and the name Pseudopleurochloris antarctica is proposed.

The production and composition of extracellular polymeric substances (EPS) in axenic batch cultures of the benthic marine epipelic diatoms Navicula salinarum and Cylindrotheca closterium were investigated. EPS was secreted into the medium and the bulk was loosely associated with the cells. Neither N. salinarum nor C. closterium formed a well-defined polysaccharide capsule. EPS of both N. salinarum and C. closterium consisted predominantly of polysaccharide but small quantities of protein were present as well. EPS also contained uronic acids and SO42− groups. Analysis of monosaccharides using gas chromatography showed that for both species glucose and xylose were the main constituents, but several other monosaccharides were present in smaller quantities. Two fractions of EPS were distinguished: a small amount was secreted into the medium and a second fraction was extracted in water at 30°C. For both species the two fractions differed somewhat in composition, indicating that they represented two different types of EPS. The EPS produced by N. salinarum and by C. closterium differed in their composition. The rate of EPS production in batch culture was highest during the transition from exponential growth to stationary growth. Negatively charged groups such as uronic acids and sulphated sugars determine the adhesion capacity of EPS and probably play an important role in the stabilization of intertidal sediments on which these diatoms grow and produce biofilms.

Energy dispersive X-ray microanalysis (XRMA) in a scanning electron microscope (SEM) was used as a method to measure elemental silicon (Si) and phosphorus (P) in dinoflagellate cysts. Cysts were prepared by quick deep freezing and then freeze-drying, thereby avoiding the addition of preservatives. Cysts of Ceratium hirundinella collected from Lake Erken, Sweden and Esthwaite Water, UK, and Ceratium furcoides collected from Esthwaite Water, were analysed and compared. The hypothesis that cysts are able to assimilate P during dormancy was tested in the laboratory by incubating newly collected cysts of C. hirundinella in medium with and without phosphate. The analyses showed that there was no difference in P content between C. hirundinella and C. furcoides, suggesting that P content reflects differences in physiological status rather than species. C. hirundinella had a significantly higher Si content than C. furcoides, which agrees with earlier studies. Comparison of cysts of C. hirundinella from different years – 1995 (stored for 1 year), 1996 and 1997 – showed that the P content in cysts from 1995 was higher than that in cysts from the following 2 years, which indicates either that P was higher during encystment in 1995 or that cysts accumulated P during dormancy. The P uptake experiment showed a very slightly, but significantly, higher, P content in cysts incubated in P-rich medium.

The ultrastructure of Peridinium cinctum, was examined by serial sectioning with particular emphasis on the detailed construction of the flagellar apparatus. The pusular system of P. cinctum included two sac pusules in open connection with the flagellar canals; disorganized material was found inside the pusules and near the flagellar pores, indicating excretory activity of the pusules. Several cells had replicated basal bodies, which were oriented toward the cell apex. The functional basal bodies formed an angle of about 65° and were linked by a layered connective, a structure so far seen only in peridinioids. A transverse microtubular root looped around the transverse flagellar canal and nucleated several rows of microtubular extensions that lined most of the transverse sac pusule. A single-stranded root was associated with the surface of the longitudinal basal body almost at a right angle to the basal body triplets. A fibrous connective between the transverse striated root and the longitudinal microtubular root was absent. The striated collars encircling the flagellar pores had a complex structure and were linked by a large connective; a smaller fibrous connective was also found in one cell. An extension of the longitudinal striated collar lined part of the longitudinal sac pusule; it showed a tubular substructure and was perhaps contractile. Bacteria were present in the peripheral cytoplasm of the cell, enveloped by several unit membranes and surrounded by vacuoles; near the sac pusules they appeared disorganized with aggregated ribosomes, possibly the result of digestion.