Hematodinium is a parasitic dinoflagellate of numerous crustacean species, including the economically important Atlantic snow crab, Chionoecetes opilio. The parasite was cultured in vitro in modified Nephrops medium at 0°C and a partial characterization of the life stages was accomplished using light and transmission electron microscopy (TEM). In haemolymph from heavily infected snow crabs two life stages were detected; amoeboid trophonts and sporonts. During in vitro cultivation, several Hematodinium sp. life stages were observed: trophonts, clump colonies, sporonts, arachnoid sporonts, sporoblasts and dinospores. Cultures initiated with sporonts progressed to motile dinospores; however, those initiated with amoeboid trophonts proliferated, but did not progress or formed schizont-like stages which were senescent artefacts. Plasmodial stages were associated with both trophonts and sporonts and could be differentiated by the presence of trichocysts on TEM. Macrodinospores were observed but not microdinospores; likely due to the low number of Hematodinium sp. cultures that progressed to the dinospore stage. No early life stages including motile filamentous trophonts or gorgonlocks were observed as previously noted in Hematodinium spp. from other crustacean hosts. All Hematodinium sp. life stages contained autofluorescent, membrane-bound electron dense granules that appeared to degranulate or be expelled from the cell during in vitro cultivation.

Following the ‘Volgoneft-248’ oil spill, phytoplankton distribution within the affected area was investigated for two years. Simultaneously measured physical variables such as salinity, temperature, Secchi disc, current speed and direction, and total petroleum hydrocarbons (TPH) were evaluated together with phytoplankton data. At the time of the accident, the TPH concentration in surface water was measured as 2.17 mg l−1 and decreased to 88.5 µg l−1 after five days. In the first sampling period, no diatoms were detected in surface water, while dinoflagellates were dominant in the phytoplankton community. The species composition of phytoplankton changed rapidly in two months and the diatoms increased in terms of abundance and diversity. This indicated that the diatoms might be more sensitive to oil pollution than the dinoflagellates. In comparison with the historical datasets, the low phytoplankton abundance following the oil spill should be considered as the small effect of oil on the phytoplankton rather than natural variability of the ecosystem. High oil concentration in the water column caused stress on the phytoplankton and influenced the species composition negatively depending on the sensitivity of groups and the natural variability of the ecosystem.

Viable diatom and dinoflagellate resting stages were recovered from sediments in Koljö Fjord on the west coast of Sweden. To determine the maximum survival time of buried resting stages, samples from sediment depths down to 50 cm were incubated at temperatures of 3, 10 and 18 °C. Sediment cores were dated by 210Pb and the age of samples containing viable resting stages was determined using the constant rate of supply model. Dilution cultures of surface sediments allowed semiquantitative estimates of the potential seed bank. Dinoflagellate cysts from species such as Diplopsalis sp., Gymnodinium nolleri, Oblea rotunda and Protoceratium reticulatum were viable down to 15 cm depth, or 37 years old. Spores and resting cells of the diatoms Chaetoceros spp., Detonula confervacea and Skeletonema costatum were viable to over 40 cm depth, and may have been buried for many decades. The seed bank of living resting stages in surficial sediments was found to be rich (c. 57000 diatom resting stages g−1 wet weight and c. 200 dinoflagellate cysts g−1 wet weight), and the percentage of viable resting stages was higher for spore- and cyst-forming species. The oxygen-deficient sediments in Koljö Fjord appear to be a natural conservator of cell viability, a condition not easily simulated in laboratory studies. These results are ecologically important since spores and cysts are a repository of genetic material able to repopulate waters if resuspended and exposed to suitable light, temperature and nutrients.

Three sand-dwelling species of the marine dinoflagellate genus Sinophysis were examined from intertidal and subtidal North German Wadden Sea sand and are illustrated by light and scanning electron microscopy. Two are described as new: S. stenosoma sp. nov. and S. grandis sp. nov. Sinophysis stenosoma sp. nov. is compressed laterally with a cell size of 37–56 μm long and 21–33 μm wide, a length/width ratio of 1·43–1·89, an epitheca width (dorsoventrally) of 5·5–8·0 μm, and a sulcus length of about half the cell length. Sinophysis grandis sp. nov. is compressed laterally with a cell size of 50–59 μm long and 35·0–41·5 μm wide, a length/width ratio of 1·29–1·61, an epitheca width (dorsoventrally) of 12–17 μm, and a sulcus length of about three-quarters the cell length. The third species, Sinophysis ebriolum (Herdman) Balech, is the most common species in the Wadden Sea. All species occur throughout the year and are all sand-dwelling, non-photosynthetic, with a smooth theca. They can be distinguished by size, length/width ratio, epitheca size, relative sulcal length and thecal pore pattern. A key to the five known Sinophysis species is provided.

Light microscopy and scanning electron microscopy were used to study Amphidinium glabrum sp. nov., a new dinoflagellate species from tidal sand flats in the North German Wadden Sea and from the surface water and the lowermost layer of first-year ice in the European Arctic. Cells are strongly flattened dorso-ventrally, with nearly parallel sides in ventral view. The distal region of the strongly displaced cingulum is not connected with the sulcus. There is no surface striation. The sulcus extends from the antapex, where it forms a large excavation, to the apex and further onto the dorsal side of the epicone. The new species is compared with two morphologically similar dinoflagellates: A. scissum Kofoid & Swezy and A. scissoides Lebour. Characters that distinguish the three taxa are: cell shape and size, shape of epicone and hypocone, cell surface, cingulum displacement, distal region of the cingulum and antapical notch.

The effect of N- and P-limitation on the growth and paralytic shellfish toxin content of Alexandrium fundyense was studied in a series of batch cultures in which the N[ratio ]P supply mass ratio was varied from less than 1 up to 160 (cf. Redfield ≡ 7·2). N- and P-limitation of growth was observed at the lower and higher ratios respectively, with dual limitation between. Cellular parameters were similar during the exponential phase of growth, regardless of external N[ratio ]P ratio. Upon nutrient exhaustion cell yields and internal pools were affected, although these also varied according to the N-source (nitrate vs. ammonium). Generally N-limitation alone led to a higher C[ratio ]N ratio, lower C[ratio ]P and N[ratio ]P ratios and a decreased toxin content in stationary-phase cells. P-limitation led to increased cell size and cell quotas, lower C[ratio ]N ratios, and higher C[ratio ]P and N[ratio ]P ratios (to maxima of 350 and 35 respectively). Complex internal P-fractionation schemes were found unnecessary to determine the P-status of cells and extraction using potassium persulphate, cold water and cold HCl alone were adequate. Severe P-limitation led to increased toxin content but only when N was also limiting, suggesting a synergistic effect of N and P availability on toxin synthesis and turnover. A positive relationship was found between toxin content and the intracellular concentration of arginine, but this varied with the nutrient status (in particular P-status) of the cells.

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 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.

The elemental composition of Ceratium hirundinella was determined in mixed phytoplankton samples collected over a 2-month period (late June to early September 1995). Electron probe X-ray microanalysis spectra of single cells routinely showed clear peaks of monovalent (Na, K) and divalent (Mg, Ca) cations, plus Si, P, S and Cl. Considerable variation in elemental concentrations occurred both within and between samples (20 cells). The overall ratio of monovalent to divalent cations was relatively constant at about 1.3. Intracellular concentrations of anions/cations and electronegative/electropositive elements were significantly correlated in most samples, suggesting a controlled internal balance of these ionic groups. Correlation analysis of elemental concentrations revealed clear patterns of statistical association within individual samples, with significant positive correlations between particular pairs of elements (Mg–P, K–Cl and K–P). Some pairs of highly correlated elements (particularly Mg–P) occurred in defined ratios throughout the samples, while others (e.g. K–Cl, Na–Mg) were variable. Factor analysis showed that elemental associations were determined by two Principal Factors in most samples, possibly related to insoluble and soluble components of cells. Decrease in the level of available P in lake water was associated with a sharp decrease in the intracellular P concentration and the concentration of other correlated elements. The estimated C/P ratio markedly differed from the classical (Redfield) value at times of low P availability. The concentration of P in cells of Ceratium was approximately 104 times greater than in the surrounding water medium (total P) compared with values of 102–103 for K.

The effects of toxic and non-toxic strains of Alexandrium sp. on the initial feeding responses of the Pacific oyster Crassostrea gigas were determined by continuous monitoring of the clearance rate of individual oysters. This was determined fluorometrically by loss of fluorescence of live microalgae introduced as food. Feeding oysters with toxic or non-toxic A. tamarense and toxic A. fundyense resulted in stop/start clearance behaviour. In contrast, control oysters fed a reference microalga, Isochrysis sp., known to support their growth, did not exhibit this behavior. Pacific oysters acclimated to Isochrysis sp., fed mixtures of Alexandrium/Isochrysis, showed further evidence of stop/start clearance. Exposure for periods up to 48 hours with non-toxic A. tamarense did not enhance clearance of either Alexandrium or Isochrysis.

Dinoflagellates are common and often important parasites of aquatic organisms, but their developmental cycles are poorly known and have not been established in in vitro culture. The parasitic dinoflagellate (Hematodinium sp.) associated with mortality of the Norway lobster (Nephrops norvegicus) in British waters has been cultivated in vitro in 10% foetal calf serum in a balanced Nephrops saline. In culture the parasite undergoes a characteristic cycle of development. Circulating sporoblasts from the host's haemolymph in vitro generate 2 kinds of flagellated uninucleate dinospore, macrospores and microspores, either of which will, after 5 weeks in fresh medium, germinate to produce multinucleate unattached filamentous trophonts. These trophonts multiply by fragmentation and growth and may be serially subcultured in this form, at 2 week intervals, indefinitely. If not subcultured, the filamentous trophonts give rise to colonies of radiating filaments (‘gorgonlocks’) which subsequently attach to the substratum to form flattened web-like ‘arachnoid’ multi-nucleate trophonts. Arachnoid trophonts become arachnoid sporonts when they synthesize trichocysts and flagellar hairs and may give rise to secondary arachnoid sporonts or to dinospores which initiate a new cycle.