INFLUENCE OF PHOSPHORUS LIMITATION ON TOXICITY AND PHOTOSYNTHESIS OF ALEXANDRIUM MINUTUM (DINOPHYCEAE) MONITORED BY IN‐LINE DETECTION OF VARIABLE CHLOROPHYLL FLUORESCENCE1

The effects of phosphorus (P) limitation on growth, toxicity, and variable chl fluorescence of Alexandrium minutum were examined in batch culture experiments. Cell division was greatly impaired in P‐limited cultures, but P spiking of these cultures after 9 days stimulated high levels of cell division equivalent to P‐replete cultures. The cellular concentration of paralytic shellfish toxins was consistent over the growth cycle of control cultures from lag phase into logarithmic growth phase, with toxins repeatedly lost to daughter cells during division. The low level of cell division in P‐limited cultures resulted in a 10‐fold increase of cellular toxin compared with controls, but this dropped upon P spiking due to increased rates of cell division. The history of phosphorus supply had an important effect on toxin concentration, with the P‐limited and the P‐spiked cultures showing values 2‐fold higher than the P‐replete cultures. Toxin profiles of the A. minutum strain used in these experiments were dominated by the N₁‐hydroxy toxins, gonyautoxins (GTX) GTX1 and GTX4, which were approximately 40 times more abundant than their analogues, GTX2 and GTX3, in P‐limited cultures. The dominance of the N₁‐hydroxy toxins increased significantly in control cultures as they advanced through logarithmic growth. In‐line measurements of the variable chl fluorescence of light‐adapted cells indicated consistent photochemical efficiency under P‐replete conditions. P limitation induced a drop in fluorescence‐based photochemical efficiency that was reversible by P spiking. There was an inverse linear relationship between in‐line fluorescence and cell toxin quota (r = ?0.88). Monitoring fluorescence in‐line may be valuable in managing efficient biotechnological production of toxins.     

Toxic Alexandrium minutum (Dinophyceae) from Vietnam with new gonyautoxin analogue

Clonal cultures of Alexandrium species collected from a shrimp pond on the northern coast of Vietnam were established and morphologically identified as Alexandrium minutum. Nucleotide sequences of domains 1 and 2 of the large subunit ribosomal (LSU) rRNA gene showed high sequence similarity to A. minutum isolates from Malaysia. Paralytic shellfish toxin profile of the clones was characterized by the dominance of GTX4, GTX1, and NEO. GTX3, GTX2, and dcSTX were also present in trace amount. Toxin content varied among the strains and growth stages, ranged from 3.0 to 12.5 fmol cell⁻¹. In addition to these known toxin components, a new gonyautoxin derivative was detected by HPLC, eluting between GTX4 and GTX1. The peak of this compound disappeared under non-oxidizing HPLC condition but unchanged either after treated with 0.05 M ammonium phosphate/10% mercaptoethanol or 0.1N HCl hydrolysis. LCMS ion scanning showed a parental ion of [M + H]⁺ at m/z 396, [M − SO₃]⁺ at m/z 316, and [M − SO₄]⁺ at m/z 298. Based on these results, the derivative was identified as deoxy-GTX4-12ol, and this represents the first report of this toxin analogue.     

The Stream Inlet to a Shallow Bay of a Drinking Water Reservoir,a ‘Hot‐Spot’ for Microcystis Blooms Initiation

Stream inlets into shallow bays of reservoirs and lakes may be ‘hot‐spots’ for toxic cyanobacterial bloom initiation. These ‘hot‐spots’ may be connected with the permanent inflow of high nutrient concentrations from the catchment, optimal physical conditions (wind protected areas) that occur in shallow areas and/or ineffective top‐down control. Four sampling sites along a transect from stream to reservoir in a shallow bay of Sulejow Reservoir (Poland) were studied to test the above hypothesis, comprising a transition zone between lotic and pelagic habitats. Investigations showed that stream inlet into shallow bay acted as incubator for Microcystis blooms. The nutrient level, especially phosphorus, was identified as the major cause of cyanobacterial bloom growth. The increase of Microcystis biomass strongly correlated with increasing microcystin concentrations, however, a relationship with microcystin content was not observed. Toxicity of bloom demonstrated seasonal variability, reaching its maximum at the initial phase of bloom. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Warm temperature acclimation impacts metabolism of paralytic shellfish toxins from Alexandrium minutum in commercial oysters

Species of Alexandrium produce potent neurotoxins termed paralytic shellfish toxins and are expanding their ranges worldwide, concurrent with increases in sea surface temperature. The metabolism of molluscs is temperature dependent, and increases in ocean temperature may influence both the abundance and distribution of Alexandrium and the dynamics of toxin uptake and depuration in shellfish. Here, we conducted a large‐scale study of the effect of temperature on the uptake and depuration of paralytic shellfish toxins in three commercial oysters (Saccostrea glomerata and diploid and triploid Crassostrea gigas, n = 252 per species/ploidy level). Oysters were acclimated to two constant temperatures, reflecting current and predicted climate scenarios (22 and 27 °C), and fed a diet including the paralytic shellfish toxin‐producing species Alexandrium minutum. While the oysters fed on A. minutum in similar quantities, concentrations of the toxin analogue GTX1,4 were significantly lower in warm‐acclimated S. glomerata and diploid C. gigas after 12 days. Following exposure to A. minutum, toxicity of triploid C. gigas was not affected by temperature. Generally, detoxification rates were reduced in warm‐acclimated oysters. The routine metabolism of the oysters was not affected by the toxins, but a significant effect was found at a cellular level in diploid C. gigas. The increasing incidences of Alexandrium blooms worldwide are a challenge for shellfish food safety regulation. Our findings indicate that rising ocean temperatures may reduce paralytic shellfish toxin accumulation in two of the three oyster types; however, they may persist for longer periods in oyster tissue.     

Growth and toxin production of tropical <Emphasis Type="Italic">Alexandrium minutum</Emphasis> Halim (Dinophyceae) under various nitrogen to phosphorus ratios

Effects of nitrogen to phosphorous (N/P) ratios of two nitrogen sources (nitrate and ammonium) on growth and toxin production of a tropical estuarine dinoflagellate, Alexandrium minutum Halim, were examined using a strain isolated from a bloom at Tumpat Estuary, Malaysia in September 2001. Experiments were carried out in batch cultures, using either nitrate (N-NO₃) or ammonium (N-NH₄) as the nitrogen source at a constant amount, and with initial N/P ratios ranging from 5 to 500. Cell density, residual N and P in the medium, cellular toxin quota (Q _t), and toxin composition were analyzed throughout the growths. Our results showed that cell densities and growth rates of A. minutum were severely suppressed under high N/P ratios (>100) in both N-NO₃ and N-NH₄ treatments. Cells tended to be larger at lower growth rate and P-limited cultures. Toxin profile was relatively constant throughout the experiments, with GTX4/GTX1 as the dominant toxin congeners. Cellular toxin quota (Q _t) increased with elevated N/P ratios in both N-NO₃ and N-NH₄ treatments. Toxin production rate, R _tox, however was enhanced in N-NH₄-grown cultures when P was limited, but showed no difference between N-NO₃- and N-NH₄-grown cultures when P was replete. Our results clearly showed that N/P ratios as well as the nitrogen compounds not only affected the growth of A. minutum, but also the cellular toxin quota and its toxin production rate.     

Toxin composition variations in cultures of Alexandrium species isolated from the coastal waters of southern China

The composition of the paralytic shellfish toxins (PSTs) of five Alexandrium tamarense strains isolated from the coastal waters of southern China and one Alexandrium minutum strain from Taiwan Island were investigated. A. tamarense CI01 and A. tamarense Dapeng predominantly produced C2 toxin (over 90%) with trace amounts of C1 toxin (C1), gonyautoxin-2 (GTX2) and GTX3; two strains of A. tamarense HK9301 maintained in different locations produced C1-4 toxins and GTX1, 4, 5 and 6; no PSTs were found in A. tamarense NEW, while A. minutum TW produced only GTX1-4. The toxin compositions of cultured A. tamarense strains did not vary as much during different growth phases as did the toxin composition of A. minutum TW. The toxin compositions of A. tamarense HK9301-1 did not change significantly under different salinity, light intensity, and nitrate and phosphate levels in the culture medium, although the toxin productivity varied expectably. Another strain HK9301-2 maintained in a different location produced much less toxins with a considerably different toxin composition. Under similar culture maintenance conditions for 3 years, the toxin profiles of A. tamarense HK9301-1 did not change as much as did A. tamarense CI01. Our results indicate that toxin compositions of the dinoflagellate strains are strain-specific and are subject to influence by nutritional and environmental conditions but not as much by the growth phase. Use of toxin composition in identifying a toxigenic strain requires special caution.     

Toxin profiles of natural populations and cultures ofAlexandrium minutum Halim from Galician (Spain) coastal waters

The toxin profiles of three isolates and natural populations of the PSP agentAlexandrium minutum from several Galician rías (NW Spain) was obtained by HPLC. The toxin content of cultures ofA. minutum is dominated by GTX4 (80–90%) and GTX4 (10–15%) with small amounts of GTX3 and GTX2 (less than 3% of each); similar results were obtained for natural populations ofAlexandrium from three different Galician rías, where a mixture ofA. lusitanicum Balech andA. minutum can occur. Important quantitative differences were found between the three isolates, one being highly and two weakly toxic. The results obtained from these isolates and natural populations ofAlexandrium were very similar to those obtained from HPLC analyses of mussels intoxicated during a PSP outbreak in Ría de Ares (Rías Altas) in 1984, confirming thatA. minutum (previously identified asGonyaulax tamarensis Lebour andAlexandrium lusitanicum) was the PSP agent during the toxic outbreak in May 1984. Toxin profiles obtained from natural populations during different PSP outbreaks in different rías and from cultures are fairly consistent and suggest that at least from the toxin point of view,A. lusitanicum andA. minutum are identical, and that the toxin profile ofA. minutum from Galicia can be used as a biochemical marker.     

A review of the global distribution of Alexandrium minutum (Dinophyceae) and comments on ecology and associated paralytic shellfish toxin profiles,with a focus on Northern Europe

Alexandrium minutum is a globally distributed harmful algal bloom species with many strains that are known to produce paralytic shellfish toxins (PSTs) and consequently represent a concern to human and ecosystem health. This review highlights that A. minutum typically occurs in sheltered locations, with cell growth occurring during periods of stable water conditions. Sediment characteristics are important in the persistence of this species within a location, with fine sediments providing cyst deposits for ongoing inoculation to the water column. Toxic strains of A. minutum do not produce a consistent toxin profile, different populations produce a range of PSTs in differing quantities. Novel cluster analysis of published A. minutum toxin profiles indicates five PST profile clusters globally. Some clusters are grouped geographically (Northern Europe) while others are widely spread. Isolates from Taiwan have a range of toxin profile clusters and this area appears to have the most diverse set of PST producing A. minutum populations. These toxin profiles indicate that within the United Kingdom there are two populations of A. minutum grouping with strains from Northern France and Southern Ireland. There is a degree of interconnectivity in this region due to oceanic circulation and a high level of shipping and recreational boating. Further research into the interrelationships between the A. minutum populations in this global region would be of value.     

Effect of salinity on growth and toxin production of <Emphasis Type="Italic">Alexandrium minutum</Emphasis> isolated from a shrimp culture pond in northern Vietnam

A clonal culture of a Vietnamese strain of Alexandrium minutum, AlexSp17, was subjected to different salinity treatments to determine the growth and toxin production of this strain that produces a novel toxin analogue, deoxy GTX4-12ol. The experiment was carried out in batch cultures without pre-acclimatization at seven salinity treatments from 5 to 35 psu, under constant temperature of 25°C, illumination of 140 μmol photon m⁻² s⁻¹, and 12:12 light/dark photoperiod. The strain grew in all salinity treatments, with optimum growth at 10–15 psu. However, the specific growth rate (0.2 day⁻¹) was lower than those reported in Malaysian strains and other strains from different geographical areas. The optimum range of salinity for the growth of this species agreed with field observations of the locality of origin. No significant change in toxin profiles was observed at different salinities. The cellular toxin quota, Qt, was not affected by the salinity-dependent growth rate. The toxin GTX4-12ol is presumed to be a transformation product of GTX4 from specific cellular reductase enzymes. Further investigation at the molecular level of toxin biosynthesis and subcellular enzyme activities is needed to provide insight in the production of this unique toxin analogue.     

Comparative study of the life cycles of Alexandrium tamutum and Alexandrium minutum (Gonyaulacales,Dinophyceae) in culture1

The microalgal genus Alexandrium includes species known to produce paralytic shellfish poisoning (PSP). Due to the importance of discriminating between HAB‐forming species, we compared the undescribed life‐cycle pattern of Alexandrium tamutum Montresor, Beran et U. John and of its toxic relative Alexandrium minutum Halim. Sexual stages, asexual and sexual division, mating type, and nuclear morphology were studied in both species. Sexual cysts are known to be morphologically identical. However, the relative size of the U‐shaped nucleus may be used to differentiate between the cysts of these species since DNA packaging in the resting cysts was lower in A. tamutum than in A. minutum, species in which the planozygote nucleus was reduced to half its volume prior to encystment. The dormancy period of the cysts was <20 d for A. tamutum, but longer than 1 month for A. minutum. In both species, cyst appearance needed to be explained by the existence of more than two sexual types (+/–), which indicates a complex heterothallic mating type. However, planozygotes of both species may divide instead of encysting. This characteristic was used for nutritional and heritage studies. Isolated planozygotes of both species encysted in larger percentages in medium deficient in both nitrates and phosphates (L/15) than in medium without phosphates added (L‐P), a medium in which most planozygotes neither divide nor encyst. Parental strains of A. minutum with and without the ventral pore formed planozygotes and, later, offspring with the ventral pore, although apparently smaller than usual. A synchronization–flow cytometry method for discriminating diploids formed by sexual fusion (planozygotes) from cells with 2C DNA content resulting from self‐duplication of DNA (dividing cells) was described. The results indicated that the maximum percentage of A. minutum planozygotes (20%) was achieved only 3 to 5 d after crossing the parental strains, and that light might not be needed for the sexual fusion and formation of planozygotes.     

Morphology, toxin composition and LSU rDNA phylogeny of Alexandrium minutum (Dinophyceae) from Denmark, with some morphological observations on other European strains

The morphology of Alexandrium minutum Halim from Denmark was studied and compared to the morphology of material from Portugal, Spain, France and Ireland. Strains from Denmark and the French coast of the English Channel differed from the typical minutum morphotype by the absence of a ventral pore. Cells without a pore also dominated field material from Ireland but a small fraction (6%) did have a pore. Many cells had a heavily areolated theca. In the exponential growth phase, the PSP-toxin profile of the Danish strain of A. minutum was dominated by C1 and C2 (up to 70%), whereas GTX2 and 3 made up more than 17%, and STX almost 13%. Cells entering the stationary phase contained 30% STX with a concomitant decrease of the other toxins. Partial large subunit rDNA sequences (664 bp) confirmed that the Danish A. minutum strain clusters together with other European strains of this species, and a strain from Australia. However, sequencing of this part of the gene did not resolve intraspecific relationships and could not differentiate populations with or without pore and/ or different toxin signatures. A strain from New Zealand had a remarkably high sequence divergence (up to 6%) compared to the other strains of A. minutum and its identity should be further investigated. A distribution map of A. minutum has been compiled and it is suggested that A. minutum and A. angustitabulatum Taylor are conspecific.     

TOXIN PROFILE,PIGMENT COMPOSITION,AND LARGE SUBUNIT RDNA PHYLOGENETIC ANALYSIS OF AN ALEXANDRIUM MINUTUM (DINOPHYCEAE) STRAIN ISOLATED FROM THE FLEET LAGOON,UNITED KINGDOM1

Paralytic shellfish toxins, pigment composition, and large subunit (LSU) rDNA sequence were analyzed for a clonal culture of Alexandrium minutum Halim isolated in 2000 from the coastal Fleet Lagoon, Dorset, United Kingdom. The HPLC pigment analysis revealed the presence of chl a, peridinin, and diadinoxanthin as major pigments and chl c₁+c₂ and c₃, diatoxanthin, and β‐carotene as minor components. The toxins responsible for paralytic shellfish poisoning were analyzed by HPLC with postcolumn derivatization and fluorescence detection. The paralytic shellfish poisoning toxin profile of the Fleet Lagoon strain of A. minutum in exponential growth phase was dominated by gonyautoxin‐3 up to 54%, whereas gonyautoxin‐2 made up 10% and saxitoxin (STX) 36%. The average toxicity of the culture was 3.8 pg STX Eq·cell^?1, and total toxin content varied from 5.6 fmol·cell^?1 on day 1 to a maximum of 16.8 fmol·cell^?1 during the early stationary phase. Sequence analysis of the LSU rDNA revealed the strain to be closely related to several European strains of A. minutum and one isolated from Australian waters, although most of these do not produce STX. The shallow Fleet Lagoon may provide a favorable environment for A. minutum to bloom, and the presence of highly potent saxitoxins in this strain indicates potential for future shellfish contamination.     

Dynamic trajectories of volatile and non‐volatile specialised metabolites in ‘overnight’ fragrant flowers of Murraya paniculata

• Ephemeral flowers, especially nocturnal ones, usually emit characteristic scent profiles within their post‐anthesis lifespans of a few hours. Whether these flowers exhibit temporal variability in the composition and profile of volatile and non‐volatile specialised metabolites has received little attention.
• Flowers of Murraya paniculata bloom in the evenings during the summer and monsoon, and their sweet, intense fragrance enhances the plant's value as an ornamental. We aimed to investigate profiles of both volatile and non‐volatile endogenous specialised metabolites (ESM) in nocturnal ephemeral flowers of M. paniculata to examine whether any biochemically diverse groups of ESM follow distinct patterns of accumulation while maintaining synchrony with defensive physiological functions.
• Targeted ESM contents of M. paniculata flowers were profiled at ten time points at 2‐h intervals, starting from late bud stage (afternoon) up to the start of petal senescence (mid‐morning). Emitted volatiles were monitored continuously within the whole 20‐h period using headspace sampling. The ESM contents were mapped by time point to obtain a highly dynamic and biochemically diverse profile. Relative temporal patterns of ESM accumulation indicated that the active fragrance‐emitting period might be divided into ‘early bloom’, ‘mid‐bloom’ and ‘late bloom’ phases. Early and late bloom phases were characterised by high free radical generation, with immediate enhancement of antioxidant enzymes and phenolic compounds. The mid‐bloom phase was relatively stable and dedicated to maximum fragrance emission, with provision for strong terpenoid‐mediated defence against herbivores. The late bloom phase merged into senescence with the start of daylight; however, even the senescent petals continued to emit fragrance to attract diurnal pollinators.
• Our study suggests that dynamic relations between the different ESM groups regulate the short‐term requirements of floral advertisement and phytochemical defence in this ephemeral flower. This study also provided fundamental information on the temporal occurrence of emitted volatiles and internal pools of specialised metabolites in M. paniculata flowers, which could serve as an important model for pollination biology of Rutaceae, which includes many important fruit crops.

     

Use of a real-time remote monitoring network (RTRM) and shipborne sampling to characterize a dinoflagellate bloom in the Neuse Estuary, North Carolina, USA

The spatial-temporal distribution of a dinoflagellate bloom dominated or co-dominated by Prorocentrum minimum was examined during autumn through early spring in a warm temperate, eutrophic estuary. The developing bloom was first detected from a web-based alert provided by a network of real-time remote monitoring (RTRM) platforms indicating elevated dissolved oxygen and pH levels in upper reaches of the estuary. RTRM data were used to augment shipboard sampling, allowing for an in-depth characterization of bloom initiation, development, movement, and dissipation. Prolonged drought conditions leading to elevated salinities, and relatively high nutrient concentrations from upstream inputs and other sources, likely pre-disposed the upper estuary for bloom development. Over a 7-month period (October 2001–April 2002), the bloom moved toward the northern shore of the mesohaline estuary, intensified under favorable conditions, and finally dissipated after a major storm. Bloom location and transport were influenced by prevailing wind structure and periods of elevated rainfall. Chlorophyll a within bloom areas averaged 106 ± 13 μg L⁻¹ (mean ± 1 S.E.; maximum, 803 μg L⁻¹), in comparison to 20 ± 1 μg L⁻¹ outside the bloom. There were significant positive relationships between dinoflagellate abundance and TN and TP. Ammonium, NO₃⁻, and SRP concentrations did not decrease within the main bloom, suggesting that upstream inputs and other sources provided nutrient-replete conditions. In addition, PAM fluorometric measurements (09:00–13:00 h) of maximal PSII quantum yield (F_v/F_m) were consistently 0.6–0.8 within the bloom until late March, providing little evidence of photo-physiological stress as would have been expected under nutrient-limiting conditions. Nitrogen uptake kinetics were estimated for P. minimum during the period when that species was dominant (October–December 2001), based on literature values for N uptake by an earlier P. minimum bloom (winter 1999) in the Neuse Estuary. The analysis suggests that NH₄⁺ was the major N species that supported the bloom. Considering the chlorophyll a concentrations during October and December and the estimated N uptake rates, phytoplankton biomass was estimated to have doubled once per day. Bloom displacement (January–February) coincided with higher diversity of heterotrophic dinoflagellate species as P. minimum abundance decreased. This research shows the value of RTRM in bloom detection and tracking, and advances understanding of dinoflagellate bloom dynamics in eutrophic estuaries.     

Combined physical,chemical and biological factors shape Alexandrium ostenfeldii blooms in The Netherlands

Harmful algal blooms (HABs) are globally expanding, compromising water quality worldwide. HAB dynamics are determined by a complex interplay of abiotic and biotic factors, and their emergence has often been linked to eutrophication, and more recently to climate change. The dinoflagellate Alexandrium is one of the most widespread HAB genera and its success is based on key functional traits like allelopathy, mixotrophy, cyst formation and nutrient retrieval migrations. Since 2012, dense Alexandrium ostenfeldii blooms (up to 4500 cells mL⁻¹) have recurred annually in a creek located in the southwest of the Netherlands, an area characterized by intense agriculture and aquaculture. We investigated how physical, chemical and biological factors influenced A. ostenfeldii bloom dynamics over three consecutive years (2013–2015). Overall, we found a decrease in the magnitude of the bloom over the years that could largely be linked to changing weather conditions during summer. More specifically, low salinities due to excessive rainfall and increased wind speed corresponded to a delayed A. ostenfeldii bloom with reduced population densities in 2015. Within each year, highest population densities generally corresponded to high temperatures, low DIN:DIP ratios and low grazer densities. Together, our results demonstrate an important role of nutrient availability, absence of grazing, and particularly of the physical environment on the magnitude and duration of A. ostenfeldii blooms. Our results suggest that predicted changes in the physical environment may enhance bloom development in future coastal waters and embayments.     

Effect of light colours and weather conditions on captures of Sogatella furcifera (Horváth) and Nilaparvata lugens (Stål)

To study the phototactic responses of white‐backed planthopper, Sogatella furcifera (Horváth) and brown planthopper, Nilaparvata lugens (Stål) to different wavelengths, four colours of light traps (blue, green, yellow and red light‐emitting diodes) were placed in the same rice field along with a traditional black light trap. This study revealed that S. furcifera and N. lugens are more attracted to blue and green lights than that to yellow and red lights. During the 24 nights, compared with the black light trap, the blue LED trap could catch more rice planthoppers at 17 nights. Furthermore, catches of other species (moths and beetles) were substantially reduced in blue LED light traps. Multiple regression models were developed to assess the effect of weather factors on light trap catches of rice planthoppers. Rainfall and mean air temperature at a night mainly affected light trap catches of S. furcifera. Higher rainfall and lower temperature increased light trap catches of S. furcifera. However, wind speed was the main factor affecting the catches of N. lugens, and the lower incidence of catches was found in the night when wind speed exceeded 3.08 m/s. S. furcifera may be flying against wind at light wind nights by 0.3–1.5 m/s, whereas N. lugens may be flying down at strong wind nights by 1.5–3.08 m/s. Relative humidity did not significantly influence on trap catches. Consequently, light wavelengths, precipitation, average temperature and wind should be considered when monitoring rice planthoppers by light traps. Therefore, the blue LED light traps are worth using for monitoring planthoppers.     

Species‐specific physiological response of dinoflagellates to quantified small‐scale turbulence1

Turbulence has been shown to alter different aspects of the physiology of some dinoflagellates. The response appears to be species‐specific and dependent on the experimental design and setup used to generate small‐scale turbulence. We examined the variability of the response of three dinoflagellate species to the turbulence, following the same experimental design used by Berdalet (1992) on Akashiwo sanguinea (Hirasaka) Ge. Hansen et Moestrup (=Gymnodinium nelsonii G. W. Martin). In all experiments, turbulence was generated by an orbital shaker at 100 rpm, which corresponded on bulk average, to dissipation rates (ε, quantified using an acoustic Doppler velocimeter) of ≈2 cm² · s^?3. Turbulence did not appreciably affect Gymnodinium sp., a small dinoflagellate. However, Alexandrium minutum Halim and Prorocentrum triestinum J. Schiller exhibited a reduced net growth rate (33% and 28%, respectively) when shaken during the exponential growth phase. Compared to the still cultures, the shaken treatments of A. minutum and P. triestinum increased the mean cell volume (up to 1.4‐ and 2.5‐fold, respectively) and the mean DNA content (up to 1.8‐ and 5.3‐fold, respectively). Cultures affected by turbulence recovered their normal cell properties when returned to still conditions. The swimming speed of the cells exposed to agitation was half that of the unshaken ones. Overall, the response of A. minutum and P. triestinum was similar, but with lower intensity, to that observed previously on A. sanguinea. We found no clear trends related to taxonomy or morphology.