Cells of the potentially toxic dinoflagellate Alexandrium catenella have a complement of features typical of dinoflagellates, including dinokaryon, pusule and amphiesma. No endosymbiotic bacteria were found in the Californian strain examined, which is weakly toxic. The chloroplast consists of a central pyrenoid complex with radiating chloroplast lobes, an arrangement found also in certain other gonyaulacoid dinoflagellates. Cells are often arranged in few-celled chains and a cytoplasmic connection interconnects adjoining cells. Striated fibres line the attachment canal and also subtend the apical pore, making up an ‘apical fibrous complex’. The flagellar apparatus basically resembles that of other gonyaulacoids. However, Alexandrium catenella, Gonyaulax spinifera and Protoceratium reticulatum share the presence of two striated collar connectives and a single-stranded microtubular root associated with the longitudinal basal body, in addition to the multi-stranded root characteristic of dinoflagellates in general. Ultrastructural features indicate that these three species are closely related while Ceratium furcoides, another gonyaulacoid dinoflagellate, apparently lacks these features.

The coldwater dinoflagellate Peridiniella catenata has been examined by light and electron microscopy. The fine-structure resembles that of other dinoflagellates with regard to the dinokaryon, the chloroplast enveloped by three membranes, and the pusule. The flagellar apparatus also resembles that of most other dinoflagellates. The main difference is a missing or reduced striated root connective between the longitudinal microtubular flagellar root and the transverse striated flagellar root. The amphiesma includes a scale-like layer on the outside of the plasmalemma. Another unusual feature is the presence of two distinct size classes of trichocysts, measuring c. 0.2×1 μm and c. 0.7×4 μm, respectively. In their detailed construction they resemble those of other dinoflagellate trichocysts. Peridiniella catenata differs from other gonyaulacoid dinoflagellates in the presence of chloroplasts with single-stalked pyrenoids and in details of the pusular complex. The presence of two size categories of trichocysts and the outer scale-like layer have not been observed in other gonyaulacoid dinoflagellates, indicating that P. catenata is not closely related to these dinoflagellates. However, the presence of two striated collar connectives in P. catenata, a feature hitherto observed only in gonyaulacoids, implies affinity to this group.

Carbon and nitrogen contents of two intertidal fucoid species, Fucus serratus and Himanthalia elongata, were investigated with respect to variations in seasonal resource availability, growth and reproductive requirements. The linear growth rate of F. serratus peaked in spring at 2·3 cm 28 d−1, compared with <0·1 cm 28 d−1 in the winter. In H. elongata, the button diameter increased slowly throughout the year (<0·22 cm 28 d−1) ; in contrast, the receptacle had an elongation rate of up to 7·8 cm 28 d−1 in the spring months. There was no difference in the nitrogen content (% dry weight, dwt) of the vegetative tissue of both non-reproductive and fertile thalli and receptacle tissue of F. serratus, but the nitrogen content of all three tissue types varied seasonally. Reproductive development was initiated in May when nitrogen content was at its peak (3 % dwt). Tissue nitrogen content decreased rapidly through reproductive development to a minimum of less than 1·5% dwt in August; this decrease also occurred in non-reproductive thalli. Tissue nitrogen varied between 0·5 and 1·75% dwt in the vegetative buttons on both non-reproductive and fertile H. elongata, but not in a distinct seasonal manner. Receptacle development in H. elongata was initiated in October/November. The nitrogen content of the receptacle tissue increased rapidly in the first two months of reproductive development (up to 2·5% dwt) then progressively decreased throughout the remaining period of reproductive development. There was no evidence of carbon storage in the vegetative tissues of either F. serratus or H. elongata.

Nitrogen (N) and phosphorus (P) limitation affect the photosynthetic apparatus of Dunaliella tertiolecta in markedly different ways. When grown at 0·25 d−1 (18 % of the resource-saturated maximum rate, μmax=1·39 d−1) in chemostat cultures, N- and P-limited cells were chlorotic relative to nutrient-replete controls. The lutein-to-chlorophyll a ratio increased under both N and P limitation, whereas the neoxanthin-to-chlorophyll a ratio increased only under P limitation. The ratio of accessory photoprotective pigments (α- and β-carotene) to chlorophyll a increased under N-limited conditions. Despite differences in accessory pigment complement, chlorophyll a-specific light absorption coefficients of N- and P-limited cultures did not differ significantly, and were greater than in nutrient-replete conditions. In contrast, the initial slope of the photosynthesis–irradiance (PE) response curve (αChl) declined under nutrient-limiting conditions. There were slight reductions in the maximum quantum efficiency of photosynthesis (ϕm) in N- and P-limited cells. Reductions in ϕm were accompanied by reductions in the ratio of variable to maximum fluorescence (Fv/Fm), and the ratio of the photosystem II reaction centre protein D1 to the large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). Differences in light-saturated gross photosynthesis rate, as measured by light/dark oxygen exchange, could be accounted for by changes in the abundance of the carboxylating enzyme Rubisco. Oxygen exchange and 14CO2 assimilation appeared to measure different processes in P-limited and N- limited cultures. At light-saturation, 14C-bicarbonate assimilation approximated gross photosynthesis (as measured by light/dark oxygen exchange) in P-limited cultures. In contrast, 14C-bicarbonate assimilation approximated net photosynthesis in N-limited cultures. When all culture conditions were compared, there was linear covariation of the rates of reductant supply via light absorption and photochemical charge separation with the rates of reductant demand for CO2 fixation and NO3− reduction.

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.

Annual growth per plant and allocation of growth to the stipe were measured in 2- to 4-year-old plants of Laminaria hyperborea from five stations with different degrees of wave exposure and different amounts of canopy biomass. Low growth in plants with initial stipe lengths of less than about 40 cm suggested that the presence of canopy-forming plants suppresses growth of understorey plants, and this was supported by the high lamina growth rate of understorey plants after removal of the canopy-forming plants. Canopy biomass and wave exposure were found to exert a differential effect on the growth of the age groups examined. Average annual growth per plant in 2- to 3-year-old plants decreased with increasing canopy biomass; growth of 4-year-old plants was not significantly influenced by canopy biomass, but increased with increasing wave exposure of the sites, suggesting an influence of some factor connected with wave exposure. The allocation of annual growth to stipe and lamina was also found to be influenced by canopy biomass and wave exposure. In 2- to 3-year-old plants the amount of annual growth allocated to the stipe increased with increasing canopy biomass while a positive linear regression between allocation of growth to the stipe and wave exposure was found in 4-year-old plants. Individual measurements carried out at a wave-exposed locality showed that the maximum allocation of growth to the stipe in the intermediate-sized plants occurred simultaneously with a period of rapid stipe elongation. Thus, rapid stipe growth in L. hyperborea can be associated with high allocation of annual growth to the stipe when the plants are about to grow into the canopy-forming layer. We suggest that this is due to the combined effects of suboptimal light levels within the kelp forest and high wave exposure.

Detailed studies on the sporophytes and gametophytes of Dictyopteris australis and Dictyopteris muelleri from Australia have demonstrated the usefulness of several reproductive characters in species discrimination. In D. australis, spherical sporangia that project above the thallus surface and are clustered around reflexed bundles of paraphyses contrast markedly with the angular sporangia of D. muelleri, which are embedded in the thallus and are scattered in broad fertile zones on the upper branches. In D. muelleri, tetrads of released spores enveloped by the inner sporangial wall are temporarily retained above the thallus surface on the ends of mucilaginous stalks. Sporangial stalks have not been reported in any other species of the brown algae, although egg stalks are produced by several fucalean species. Differences in oogonial structure can also be used to distinguish D. australis and D. muelleri. The spherical oogonia of D. australis, which project above the thallus surface, are conspicuously different from the angular embedded oogonia of D. muelleri. Detailed comparative studies on other species of Dictyopteris are now required to ensure that reproductive characters are used not only to define species of Dictyopteris but also to effectively circumscribe the genus.

The Japanese endemic charalean species Nitella gracilens Morioka (=N. furcata subsp. furcata var. sieberi f. gracilens) was thought to be extinct until it was rediscovered at the type locality, Lake Ashinoko, Kanagawa Prefecture. Uni-charalean cultures of N. gracilens were established and sexual organs developed and matured. The morphology of this alga, examined by light microscopy, corresponds closely with the original description by Morioka, particularly with regard to the oospores. The mature oospore walls of N. gracilens are orange or yellowish-brown and the fossa wall of the oospore is smooth or has a finely granulate ornamentation. In addition, scanning electronic microscopic examination demonstrated that the fossa walls have minute granulate structures that are compactly arranged. These observations contrast with a previous report that the oospore wall ornamentation of this taxon is reticulate. Since oospore wall ornamentation and the form of the dactyls in N. gracilens are essentially different from those of other infraspecific taxa of N. furcata sensu Wood (1965), N. gracilens should be maintained as a distinct morphological species within the genus Nitella.