Notes on the Cultivation of Two Mixotrophic Dinophysis Species and Their Ciliate Prey Mesodinium rubrum

The niche of a stress-tolerant specialist, Dinophysis acuminata, in a coastal upwelling system

Dinophysis acuminata, the main cause of shellfish harvesting bans in Europe, blooms in the Galician Rías (NW Spain) throughout the upwelling season (ca. March to September). Here we illustrate rapid changes in vertical and across ría-shelf distributions of diatoms and dinoflagellates (including D. acuminata vegetative and small cells) in Ría de Pontevedra (RP) and Ría de Vigo (RV) during transitions from spin-down to spin-up phases of upwelling cycles. A subniche approach based on a Within Outlying Mean Index (WitOMI) showed that under the transient environmental conditions met during the cruise, both vegetative and small cells of D. acuminata colonized the Ria and Mid-shelf subniches, exhibiting good tolerance and extremely high marginality, in particular the small cells. Bottom-up (abiotic) control overwhelmed biological constraints, and shelf waters became a more favourable environment than the Rías. Contrasting higher biotic constraints inside the Rías were found for the small cells, with a subniche possibly controlled by unsuitable physiological status (notwithstanding the higher density) of the vegetative cell population. Results here on behaviour (vertical positioning) and physiological traits (high tolerance but very specialized niche) of D. acuminata give new insights into the ability of this species to remain in the upwelling circulation system. Higher shelf-ría exchanges in the Ría (RP) with more dense and persistent D. acuminata blooms reveal the relevance of transient event-scales and species- and site-specific characteristics to the fate of these blooms. Earlier statements about simple linear relationships between average upwelling intensities and the recurrence of Harmful algae bloom (HAB) events in the Galician Rías Baixas are questioned.

Identification of 24-O-β-d-Glycosides and 7-Deoxy-Analogues of Okadaic Acid and Dinophysistoxin-1 and -2 in Extracts from Dinophysis Blooms, Dinophysis and Prorocentrum Cultures, and Shellfish in Europe, North America and Australasia

Two high-mass polar compounds were observed in aqueous side-fractions from the purification of okadaic acid (1) and dinophysistoxin-2 (2) from Dinophysis blooms in Spain and Norway. These were isolated and shown to be 24-O-β-d-glucosides of 1 and 2 (4 and 5, respectively) by nuclear magnetic resonance (NMR) spectroscopy, mass spectrometry, and enzymatic hydrolysis. These, together with standards of 1, 2, dinophysistoxin-1 (3), and a synthetic specimen of 7-deoxy-1 (7), combined with an understanding of their mass spectrometric fragmentation patterns, were then used to identify 1–5, the 24-O-β-d-glucoside of dinophysistoxin-1 (6), 7, 7-deoxy-2 (8), and 7-deoxy-3 (9) in a range of extracts from Dinophysis blooms, Dinophysis cultures, and contaminated shellfish from Spain, Norway, Ireland, Canada, and New Zealand. A range of Prorocentrum lima cultures was also examined by liquid chromatography–high resolution tandem mass spectrometry (LC–HRMS/MS) and was found to contain 1, 3, 7, and 9. However, although 4–6 were not detected in these cultures, low levels of putative glycosides with the same exact masses as 4 and 6 were present. The potential implications of these findings for the toxicology, metabolism, and biosynthesis of the okadaic acid group of marine biotoxins are briefly discussed.

Characterization of toxin-producing strains of Dinophysis spp. (Dinophyceae) isolated from French coastal waters, with a particular focus on the D. acuminata-complex

Dinoflagellates of the genus Dinophysis are the most prominent producers of Diarrhetic Shellfish Poisoning (DSP) toxins which have an impact on public health and on marine aquaculture worldwide. In particular, Dinophysis acuminata has been reported as the major DSP agent in Western Europe. Still, its contribution to DSP events in the regions of the English Channel and the Atlantic coast of France, and the role of the others species of the Dinophysis community in these areas are not as clear. In addition, species identification within the D. acuminata complex has proven difficult due to their highly similar morphological features. In the present study, 30 clonal strains of the dominant Dinophysis species have been isolated from French coasts including the English Channel (3 sites), the Atlantic Ocean (11 sites) and the Mediterranean Sea (6 sites). Morphologically, strains were identified as three species: D. acuta, D. caudata, D. tripos, as well as the D. acuminata-complex. Sequences of the ITS and LSU rDNA regions confirmed these identifications and revealed no genetic difference within the D. acuminata-complex. Using the mitochondrial gene cox1, two groups of strains differing by only one substitution were found in the D. acuminata-complex, but SEM analysis of various strains showed a large range of morphological variations. Based on geographical origin and morphology, strains of the subclade A were ascribed to 'D. acuminata' while those of the subclade B were ascribed to 'D. sacculus'. Nevertheless, the distinction into two separate species remains questionable and was not supported by our genetic data. The considerable variations observed in cultured strains suggest that physiological factors might influence cell contour and bias identification. Analyses of Dinophysis cultures from French coastal waters using liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) revealed species-conserved toxin profiles for D. acuta (dinophysistoxin 2 (DTX2), okadaic acid (OA), pectenotoxin 2 (PTX2)), D. caudata (PTX2) and D. tripos (PTX2), irrespective of geographical origin (Atlantic Ocean or Mediterranean Sea). Within the D. acuminata-complex, two different toxin profiles were observed: the strains of 'D. acuminata' (subclade A) from the English Channel and the Atlantic Ocean contained only OA while strains of 'D. sacculus' (subclade B) from Mediterranean Sea/Atlantic Ocean contained PTX2 as the dominant toxin, with OA and C9-esters also being present, albeit in lower proportions. The same difference in toxin profiles between 'D. sacculus' and 'D. acuminata' was reported in several studies from Galicia (NW- Spain). This difference in toxin profiles has consequences in terms of public health, and consequently for monitoring programs. While toxin profile could appear as a reliable feature separating 'D. acuminata' from 'D. sacculus' on both French and Spanish coasts, this does not seem consistent with observations on a broader geographical scale for the D. acuminata complex, possibly due to the frequent lack of genetic characterization.

Cultures of Dinophysis sacculus, D. acuminata and pectenotoxin 2 affect gametes and fertilization success of the Pacific oyster, Crassostrea gigas

Harmful algal blooms (HABs) of toxic species of the dinoflagellate genus Dinophysis are a threat to human health as they are mainly responsible for diarrheic shellfish poisoning (DSP) in the consumers of contaminated shellfish. Such contamination leads to shellfish farm closures causing major economic and social issues. The direct effects of numerous HAB species have been demonstrated on adult bivalves, whereas the effects on critical early life stages remain relatively unexplored. The present study aimed to determine the in vitro effects of either cultivated strains of D. sacculus and D. acuminata isolated from France or their associated toxins (i.e. okadaic acid (OA) and pectenotoxin 2 (PTX2)) on the quality of the gametes of the Pacific oyster Crassostrea gigas. This was performed by assessing the ROS production and viability of the gametes using flow cytometry, and fertilization success using microscopic counts. Oocytes were more affected than spermatozoa and their mortality and ROS production increased in the presence of D. sacculus and PTX2, respectively. A decrease in fertilization success was observed at concentrations as low as 0.5 cell mL^-1 of Dinophysis spp. and 5 nM of PTX2, whereas no effect of OA could be observed. The effect on fertilization success was higher when both gamete types were concomitantly exposed compared to separate exposures, suggesting a synergistic effect. Our results also suggest that the effects could be due to cell-to-cell contact. These results highlight a potential effect of Dinophysis spp. and PTX2 on reproduction and recruitment of the Pacific oyster.

Growth response of Dinophysis, Mesodinium, and Teleaulax cultures to temperature, irradiance, and salinity

Mixotrophic Dinophysis species threaten human health and coastal economies through the production of toxins which cause diarrhetic shellfish poisoning (DSP) in humans. Novel blooms of Dinophysis acuminata and Dinophysis ovum have occurred in North American waters in recent decades, resulting in the closure of shellfish harvesting. Understanding the ecology of Dinophysis species and their prey is essential to predicting and mitigating the impact of blooms of these dinoflagellates. The growth response of two new isolates of Dinophysis species, one isolate of Mesodinium rubrum, and two strains of Teleaulax amphioxeia were evaluated at a range of temperature, salinity, and irradiance treatments to identify possible environmental drivers of Dinophysis blooms in the Gulf of Mexico. Results showed optimal growth of T. amphioxeia and M. rubrum at 24 °C, salinity 30 - 34, and irradiances between 300 and 400 µmol quanta m ^- 2s ^- 1. Optimal Dinophysis growth was observed at salinity 22 and temperatures between 18 and 24 °C. Mesodinium and both Dinophysis responded differently to experimental treatments, which may be due to the suitability of prey and different handling of kleptochloroplasts. Dinophysis bloom onset may be initiated by warming surface waters between winter and spring in the Gulf of Mexico. Toxin profiles for these two North American isolates were distinct; Dinophysis acuminata produced okadaic acid, dinophysistoxin-1, and pectenotoxin-2 while D. ovum produced only okadaic acid. Toxin per cell for D. ovum was two orders of magnitude greater than D. acuminata. Phylogenies based on the cox1 and cob genes did not distinguish these two Dinophysis species within the D. acuminata complex.

Combined Effects of Temperature, Irradiance, and pH on Teleaulax amphioxeia (Cryptophyceae) Physiology and Feeding Ratio For Its Predator Mesodinium rubrum (Ciliophora)1

The cryptophyte Teleaulax amphioxeia is a source of plastids for the ciliate Mesodinium rubrum and both organisms are members of the trophic chain of several species of Dinophysis. It is important to better understand the ecology of organisms at the first trophic levels before assessing the impact of principal factors of global change on Dinophysis spp. Therefore, combined effects of temperature, irradiance, and pH on growth rate, photosynthetic activity, and pigment content of a temperate strain of T. amphioxeia were studied using a full factorial design (central composite design 2³ *) in 17 individually controlled bioreactors. The derived model predicted an optimal growth rate of T. amphioxeia at a light intensity of 400 μmol photons · m^-2 · s^-1 , more acidic pH (7.6) than the current average and a temperature of 17.6°C. An interaction between temperature and irradiance on growth was also found, while pH did not have any significant effect. Subsequently, to investigate potential impacts of prey quality and quantity on the physiology of the predator, M. rubrum was fed two separate prey: predator ratios with cultures of T. amphioxeia previously acclimated at two different light intensities (100 and 400 μmol photons · m^-2 s^-1 ). M. rubrum growth appeared to be significantly dependent on prey quantity while effect of prey quality was not observed. This multi-parametric study indicated a high potential for a significant increase of T. amphioxeia in future climate conditions but to what extent this would lead to increased occurrences of Mesodinium spp. and Dinophysis spp. should be further investigated.

Effects of small-scale turbulence on two species of Dinophysis

Dinoflagellate species of Dinophysis, in particular D. acuminata and D. acuta, produce lipophilic toxins that pose a threat to human health when concentrated in shellfish and jeopardize shellfish exploitations in western Europe. In northwestern Iberia, D. acuminata has a long growing season, from spring to early autumn, and populations develop as soon as shallow stratification forms when the upwelling season begins. In contrast, D. acuta blooms in late summer, when the depth of the pycnocline is maximal and upwelling pulses are moderate. In situ observations on the hydrodynamic regimes during the two windows of opportunity for Dinophysis species led us to hypothesize that D. acuta should be more sensitive to turbulence than D. acuminata. To test this hypothesis, we studied the response of D. acuminata and D. acuta to three realistic turbulence levels low (LT), ε ≈ 10^-6 m² s^-3; medium (MT), ε ≈ 10^-5  m² s^-3 and high (HT), ε ≈ 10^-4 m² s^-3generated by Turbogen, a highly reproducible, computer-controlled system. Cells of both species exposed to LT and MT grew at rates similar to the controls. Marked differences were found in the response to HT: D. acuminata grew slowly after an initial lag phase, whereas D. acuta cell numbers declined. Results from this study support the hypothesis that turbulence may play a role in shaping the spatio-temporal distribution of individual species of Dinophysis. We also hypothesize that, in addition to cell disturbance affecting division, sustained high shear generated by microturbulence may cause a decline in Dinophysis numbers due to decreased densities of ciliate prey.

Trends in Dinophysis abundance and diarrhetic shellfish toxin levels in California mussels (Mytilus californianus) from Monterey Bay, California

Diarrhetic shellfish toxins (DSTs) are produced by the marine dinoflagellate, Dinophysis, as well as select species of benthic Prorocentrum. The DSTs can bioaccumulate in shellfish and cause gastrointestinal illness when humans consume high levels of this toxin. Although not routinely monitored throughout the U.S., recent studies in Washington, Texas, and New York suggest DSTs may be widespread throughout U.S. coastal waters. This study describes a four-year time series (2013-2016) of Dinophysis concentration and DST level in California mussels (Mytilus californianus) from Santa Cruz Municipal Wharf (SCMW) in Monterey Bay, California. Results show a maximum Dinophysis concentration of 9404 cells/L during this study and suggest Dinophysis persists as a member of the background phytoplankton community throughout the year. In California mussels, DSTs were found at persistent low levels throughout the course of this study, and exceeded the FDA guidance level of 160 ng/g 19 out of 192 weeks sampled. Concentrations of Dinophysis alone are a positive but weak predictor of DST level in California mussels, and basic environmental variables (temperature, salinity, and nutrients) do not sufficiently explain variation in Dinophysis concentration at SCMW. This study demonstrates that Dinophysis in Monterey Bay are producing DSTs that accumulate in local shellfish throughout the year, occasionally reaching levels of concern.

Interannual Variability of Dinophysis acuminata and Protoceratium reticulatum in a Chilean Fjord: Insights from the Realized Niche Analysis

Here, we present the interannual distribution of Dinophysis acuminata and Protoceratium reticulatum over a 10-year period in the Reloncaví Fjord, a highly stratified fjord in southern Chile. A realized subniche approach based on the Within Outlying Mean Index (WitOMI) was used to decompose the species’ realized niche into realized subniches (found within subsets of environmental conditions). The interannual distribution of both D. acuminata and P. reticulatum summer blooms was strongly influenced by climatological regional events, i.e., El Niño Southern Oscillation (ENSO) and the Southern Annual Mode (SAM). The two species showed distinct niche preferences, with blooms of D. acuminata occurring under La Niña conditions (cold years) and low river streamflow whereas P. reticulatum blooms were observed in years of El Niño conditions and positive SAM phase. The biological constraint exerted on the species was further estimated based on the difference between the existing fundamental subniche and the realized subniche. The observed patterns suggested that D. acuminata was subject to strong biological constraint during the studied period, probably as a result of low cell densities of its putative prey (the mixotrophic ciliate Mesodinium cf. rubrum) usually observed in the studied area.