This is the fourth birthday of the European Journal of Phycology, and also the beginning of my fourth year as editor-in-chief. I would like to take this opportunity to thank the previous editor, Dr Roger Jones, for setting up the present structure of the journal and for initiating the present happy relationship with our publishers, Cambridge University Press. The first term of office for the Associate Editors has now ended, and many thanks are due to all of them for their contributions to the journal. We are very fortunate in that most of the Associate Editors have been able to continue in their posts, and that those retiring have been replaced by distinguished new editors. The important work done by editorial board members, new, retired and continuing, is also much appreciated. Communication between the editorial team and authors is being facilitated by wider use of e-mail and the journal now includes e-mail addresses for authors who supply them. Current instructions to authors are now available on the CUP world wide web site (see address inside journal back cover), and the contents of each issue will appear on the web site two weeks before publication.

The past decade has seen substantial breakthroughs in understanding the biochemistry, molecular biology and regulation of nitrate reductases (NR) in higher plants and green algae. In contrast, although there has been considerable interest in using various measurements of NR to provide ecophysiological information, comparable knowledge of NR is largely lacking in algal groups other than chlorophytes. Applying information about NR from chlorophytes and higher plants to other algae may be difficult. There is evidence that non-chlorophyte forms of NR are diverse and distinct in terms of biochemical characteristics and regulatory features. Key areas to be pursued in non-chlorophyte algae include the identification and adoption of model organisms for NR research in different algal groups; the creation of selected and engineered mutants; the purification, biochemical characterization and production of antibodies to different algal forms of NR; the identification of NR genes; and the undertaking of coordinated research on nitrate uptake proteins and other enzymes in pathways of nitrate assimilation.

Batch culture experime nts were conducted with Alexandrium ostenfeldii, a toxic, marine dinoflagellate common in Danish waters. Growth occurred at 11·3–23·7 °C and from 10 to 40 psu.Maximum division rates of more than 0·3 di visions d−1took place at 20 °C and 15–20 psu. Growth phase variations resulted in mean cell sizes from 12 × 103 to 20 × 103 μm3. Variations in cell size were observed at differ ent temperatures and salinities, and mean cell size was closely correlated with division rate for all temperatures investigated (11·3–23·7 °C) and for salinities between 10 and 30 psu. Sexual stages, fusing gametes and planozygotes were observed in nutrient-deficient cultures of A. ostenfeldii from New Zealand, but mixing of two Danish nutrient-deficient, clonal cultures did not result in mating. Sexual fusion did not lead to the formation of resting c ysts, which are presently known only from nature. Temporary cysts were very common in ageing cultures and in unfavourable environmental conditions that did not permit growth. These cysts showed a high degree of morphological variability. When st ained with calcofluor, the cysts revealed a surface pattern. Germination of temporary cysts caused the release of a naked, biflagellate stage. At germination, the transverse flagellum was located outside the cingulum, next to the longitudinal fl agellum. The transverse flagellum became positioned in the cingulum only after the cell was clear of the cyst wall.

The effect of low pH on growth and photosynthesis was compared in two strains of Chlorella isolated from symbiosis with Paramecium bursaria. One, 3N813A, releases large amounts of maltose at low pH; the other, NC64A, does not release maltose in culture. Maltose synthesis at low pH appeared to have a greater effect on cell growth than pH by itself. Growth of maltose-releasing 3N813A showed a direct relationship with pH; growth of non-maltose-releasing NC64A was reduced only as pH fell from 7·0 to 5·5. At pH 5·0, net photosynthetic capacity of 3N813A cells was reduced to 76% of controls at pH 7·0, but the specific growth constant (k) was reduced to 22%, and at pH 4·0 growth and nitrate uptake were inhibited. In 3N813A cells at pH 5·0, carbon (C) was diverted from cell growth, net chlorophyll synthesis, assimilation of nitrogen (N), and synthesis of protein and starch to maltose release, but C[ratio ]N ratios were unchanged. In NC54A cells, starch but not protein synthesis was inhibited at pH 5·0, and a reduction in accumulation of N led to an increase in C[ratio ]N ratios. Unlike N starvation, growth of 3N813A cells at pH 5·0 did not reduce chlorophyll content. When measured at pH 7·0 with excess bicarbonate, photosynthetic parameters of both 3N813A and NC64A cells grown at pH 5·0 were similar to those of cells grown at pH 7·0; however, net photosynthesis of 3N813A cells N starved at pH 7·0 was 22% of that of N-sufficient controls. In symbiosis, release of excess photosynthate as maltose may inhibit cell growth by inhibiting assimilation of inorganic N, but because C[ratio ]N ratios are unchanged, photosynthetic capacity of cells is not affected.

A comparative study of fertile gametophytes has been carried out on six species of the Dictyotales from Australia. Patterns of gametangial distribution and structure are similar in Zonaria angustata, Zonaria diesingiana, Zonaria spiralis and Zonaria turneriana, but there are some marked differences apparent between both Homoeostrichus olsenii and Homoeostrichus sinclairii and the Zonaria species. Sterile cortical cells and mucilage between the cylindrical oogonia are characteristic of the indusiate female sori of Zonaria, which differ markedly from the comparable structures of H. olsenii, in which all cortical cells have been transformed into oogonia and the walls of adjacent oogonia are contiguous. In contrast, the large spherical oogonia of H. sinclairii are unique in the Dictyotales, lacking a stalk cell and occurring among brown paraphyses in a large non-indusiate sorus on each terminal branch segment. Antheridial sori of the six species exhibit far less structural variation than the oogonial sori. Male sori are surrounded by undifferentiated cortical cells in H. olsenii, by tall brown paraphyses and short paraphyses in H. sinclairii and by sterile cells in Zonaria spp. Short paraphyses form only around the male sori of H. sinclairii in the Dictyotales; they differ in structure from the brown paraphyses but are similar to the antheridia, from which they may have been derived. Gametangial characters have proved invaluable in defining the genus Zonaria and in separating H. olsenii from H. sinclairii, but they cannot be used to delimit the species of Zonaria. Furthermore, the differences observed in the gametangia have provided new characters for phylogenetic analyses, as well as providing further supporting evidence for the recognition of Zonaria and Homoeostrichus as distinct entities.

Contemporary phytoplankton and palaeolimnological studies were made of the algal response to acidification and liming in three lakes in Hälsingland, central Sweden (Njupfatet, Sjösjön, Djuptjärn). Surveys and experimental studies of the phytoplankton response to liming were undertaken at Njupfatet, together with an experiment designed to determine the possible role of lake sediments as an inoculum for any new species arriving in the water column. Liming had little quantitative or qualitative effect on the phytoplankton diversity at Njupfatet, but did result in the loss of the dominant contributor to algal biomass, Merismopedia tenuissima. None of the four new species recorded in the lake following liming was hatched from the sediment inoculum experiment. A freeze core from Njupfatet was dated by 210Pb and carbonaceous fly-ash particle profiles were also determined for Njupfatet and Sjösjön, which provided an approximate chronology for the latter lake. Diatom analyses were made of the three lakes and pH and dissolved organic carbon inferred using weighted averaging methodology. Njupfatet had no planktonic diatoms over the last 200–300 years, and was dominated by benthic diatoms, but the diatom-inferred pH suggests that the lake was acidified to pH < 5 prior to liming in 1989. Both Djuptjärn and Sjösjön were dominated by planktonic diatoms, and were acidifying from (c. 1970) prior to liming, Sjösjön from pH 6 to ∼ 5 and Djuptjärn from 6·5 to ∼ 5·5. These pH inferences suggest that at least some lakes in this region are susceptible to atmospheric acidification. The response of the diatoms to liming is discussed, in particular the rapid expansion at Njupfatet, of Cyclotella glomerata a diatom which was also present in Sjösjön for a period prior to acidification, and at other lakes in south-west Sweden. Possible reasons for the expansion of this small centric diatom are discussed.

Enteromorpha intestinalis grows along the Swedish west coast in rockpools which are isolated from the open seawater for long time periods and where, therefore, the inorganic carbon content is low and the pH is high during the day. In order to investigate how E. intestinalis could grow under such apparently CO2-constraining conditions, we measured its photosynthetic responses to inorganic carbon in the presence of an inhibitor of external/surface-bound carbonic anhydrase (acetazolamide) as well as an inhibitor of HCO−3 transport via anion exchange (4,4′-diisothiocyanatostilbene-2,2′-disulfonate). The results show that both HCO−3 dehydration via surface-bound carbonic anhydrase and HCO−3 transport via a 4,4′-diisothiocyanatostilbene-2,2′-disulfonate-sensitive mechanism were present in E. intestinalis, but only HCO−3 uptake via the putative transporter was operative in rockpool water during most of the photic period (pH > 9·4, inorganic carbon < 0·45 mol m−3 and CO2 < 0·05 mmol m−3). The advantage of such a mechanism, rather than extracellular HCO−3 dehydration, is discussed with regard to photosynthesis of marine macroalgae under in situ conditions conducive to high pH values adjacent to the thalli.

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.

Phytoplankton studies in the North Atlantic have revealed coccoliths of Neosphaera coccolithomorpha and Ceratolithus cristatus occurring on the same cell. This may indicate that each of these species represents a stage of one coccolithophorid life cycle, in which each phase possesses a different heterococcolith type. However, definitive evidence for this is lacking.