Influence of Temperature on Growth and Production of Pectenotoxin-2 by a Monoclonal Culture of Dinophysis caudata

Role of turbulence in Dinophysis spp. growth, feeding, and toxin leakage in culture

Dinophysis, a mixotrophic dinoflagellate that is known to prey on the ciliate Mesodinium rubrum, and retain its chloroplasts, is responsible for diarrhetic shellfish poisoning (DSP) in humans and has been identified on all U.S. coasts. Monocultures of Dinophysis have been used to investigate the growth of Dinophysis species in response to variations in environmental conditions, however, little is known about the roles of system stability (turbulence) and mixotrophy in the growth and toxicity of Dinophysis species in the U.S.. To begin to address this gap in knowledge, culturing experiments were conducted with three species (four strains) of Dinophysis, that included predator-prey co-incubation (Dinophysis spp.+ M. rubrum) and prey-only (M. rubrum) flasks. Cultures were investigated for effects of low or high turbulence on Dinophysis spp. growth, feeding, and amounts of intra- and extracellular toxins: okadaic acid and derivatives (diarrhetic shellfish toxins, DSTs) and pectenotoxins (PTXs). Turbulence did not have a measurable effect on the rates of ingestion of M. rubrum prey by Dinophysis spp. for any of the four strains, however, effects on growth and particulate and dissolved toxins were observed. High turbulence (ε = 10-2 m2s-3) significantly slowed growth of both D. acuminata and D. ovum relative to still controls, but significantly stimulated growth of the D. caudata strain. Increasing turbulence also resulted in significantly higher intracellular toxin content in D. acuminata cultures (DSTs and PTXs), but significantly reduced intracellular toxin content (PTXs) in those of D. caudata. An increase in turbulence appeared to promote toxin leakage, as D. ovum had significantly more extracellular DSTs found in the medium under high turbulence when compared to the still control. Overall, significant responses to turbulence were observed, whereby the three strains from the "Dinophysis acuminata complex" displayed a stress response to turbulence, i.e., decreasing growth, increasing intracellular toxin content and/or increasing toxin leakage, while the D. caudata strain had an opposite response, appearing stimulated by, or more tolerant of, high turbulence.

A survey of Dinophysis spp. and their potential to cause diarrhetic shellfish poisoning in coastal waters of the United States

Multiple species of the genus Dinophysis produce diarrhetic shellfish toxins (okadaic acid and Dinophysis toxins, OA/DTXs analogs) and/or pectenotoxins (PTXs). Only since 2008 have DSP events (illnesses and/or shellfish harvesting closures) become recognized as a threat to human health in the United States. This study characterized 20 strains representing five species of Dinophysis spp. isolated from three US coastal regions that have experienced DSP events: the Northeast/Mid-Atlantic, the Gulf of Mexico, and the Pacific Northwest. Using a combination of morphometric and DNA-based evidence, seven Northeast/Mid-Atlantic isolates and four Pacific Northwest isolates were classified as D. acuminata, a total of four isolates from two coasts were classified as D. norvegica, two isolates from the Pacific Northwest coast were identified as D. fortii, and three isolates from the Gulf of Mexico were identified as D. ovum and D. caudata. Toxin profiles of D. acuminata and D. norvegica varied by their geographical origin within the United States. Cross-regional comparison of toxin profiles was not possible with the other three species; however, within each region, distinct species-conserved profiles for isolates of D. fortii, D. ovum, and D. caudata were observed. Historical and recent data from various State and Tribal monitoring programs were compiled and compared, including maximum recorded cell abundances of Dinophysis spp., maximum concentrations of OA/DTXs recorded in commercial shellfish species, and durations of harvesting closures, to provide perspective regarding potential for DSP impacts to regional public health and shellfish industry.

Growth, Toxin Content and Production of Dinophysis Norvegica in Cultured Strains Isolated from Funka Bay (Japan)

The successful cultivation of Dinophysis norvegica Claparède & Lachmann, 1859, isolated from Japanese coastal waters, is presented in this study, which also includes an examination of its toxin content and production for the first time. Maintaining the strains at a high abundance (>2000 cells per mL^-1) for more than 20 months was achieved by feeding them with the ciliate Mesodinium rubrum Lohmann, 1908, along with the addition of the cryptophyte Teleaulax amphioxeia (W.Conrad) D.R.A.Hill, 1992. Toxin production was examined using seven established strains. At the end of the one-month incubation period, the total amounts of pectenotoxin-2 (PTX2) and dinophysistoxin-1 (DTX1) ranged between 132.0 and 375.0 ng per mL^-1 (n = 7), and 0.7 and 3.6 ng per mL^-1 (n = 3), respectively. Furthermore, only one strain was found to contain a trace level of okadaic acid (OA). Similarly, the cell quota of pectenotoxin-2 (PTX2) and dinophysistoxin-1 (DTX1) ranged from 60.6 to 152.4 pg per cell^-1 (n = 7) and 0.5 to 1.2 pg per cell^-1 (n = 3), respectively. The results of this study indicate that toxin production in this species is subject to variation depending on the strain. According to the growth experiment, D. norvegica exhibited a long lag phase, as suggested by the slow growth observed during the first 12 days. In the growth experiment, D. norvegica grew very slowly for the first 12 days, suggesting they had a long lag phase. However, after that, they grew exponentially, with a maximum growth rate of 0.56 divisions per day (during Days 24-27), reaching a maximum concentration of 3000 cells per mL^-1 at the end of the incubation (Day 36). In the toxin production study, the concentration of DTX1 and PTX2 increased following their vegetative growth, but the toxin production still increased exponentially on Day 36 (1.3 ng per mL^-1 and 154.7 ng per mL^-1 of DTX1 and PTX2, respectively). The concentration of OA remained below detectable levels (≤0.010 ng per mL^-1) during the 36-day incubation period, with the exception of Day 6. This study presents new information on the toxin production and content of D. norvegica, as well as insights into the maintenance and culturing of this species.

New Knowledge on Distribution and Abundance of Toxic Microalgal Species and Related Toxins in the Northwestern Black Sea

Numerous potentially toxic plankton species commonly occur in the Black Sea, and phycotoxins have been reported. However, the taxonomy, phycotoxin profiles, and distribution of harmful microalgae in the basin are still understudied. An integrated microscopic (light microscopy) and molecular (18S rRNA gene metabarcoding and qPCR) approach complemented with toxin analysis was applied at 41 stations in the northwestern part of the Black Sea for better taxonomic coverage and toxin profiling in natural populations. The combined dataset included 20 potentially toxic species, some of which (Dinophysis acuminata, Dinophysis acuta, Gonyaulax spinifera, and Karlodinium veneficum) were detected in over 95% of the stations. In parallel, pectenotoxins (PTX-2 as a major toxin) were registered in all samples, and yessotoxins were present at most of the sampling points. PTX-1 and PTX-13, as well as some YTX variants, were recorded for the first time in the basin. A positive correlation was found between the cell abundance of Dinophysis acuta and pectenotoxins, and between Lingulodinium polyedra and Protoceratium reticulatum and yessotoxins. Toxic microalgae and toxin variant abundance and spatial distribution was associated with environmental parameters. Despite the low levels of the identified phycotoxins and their low oral toxicity, chronic toxic exposure could represent an ecosystem and human health hazard.

Occurrence, spatial distribution, and partitioning behavior of marine lipophilic phycotoxins in the Pearl River Estuary, South China

The occurrence, spatial distribution, and partitioning behavior of 17 marine lipophilic phycotoxins (MLPs) in surface and bottom seawater, particulate organic matter (POM), and surface sediment from the Pearl River Estuary (PRE) were investigated to understand current contamination and the potential risks to marine ecosystems in this region. Nine MLPs were detected, including azaspiracid1-3, gymnodimine, okadaic acid, dinophysistoxin 1-2, pectenotoxin2 (PTX2), and homoyessotoxin, with Σ₁₇MLP concentrations ranging 545-12,600 pg L^-1 and 619-8,800 pg L^-1 in surface and bottom seawater, respectively; 0-294 ng g^-1 and 0.307-300 ng g^-1 dry weight (dw) in surface and bottom POM, respectively; and 3.90-982 pg g^-1 dw in surface sediment. Lower Σ₁₇MLP levels in the seawater were found at the mouth of the PRE, and gradually increased with increasing distance offshore. According to the calculated partition coefficient, the affinity of MLPs for the aquatic environment components was as follows (from highest to lowest): POM > seawater > sediment. Overall, the distribution and migration of MLPs in the PRE may depend on partition coefficients, the organic carbon fraction, and environmental factors.

Karlodinium veneficum: Growth optimization, metabolite characterization and biotechnological potential survey

AIM OF THIS STUDY

The major aim of this work was to consistently optimize the production of biomass of the dinoflagellate Karlodinium veneficum and evaluate its extracts biotechnological potential application towards food, nutraceutical or/and pharmaceutical industries.

METHODS AND RESULTS

A successful approach of biomass production of K. veneficum CCMP 2936 was optimized along with the chemical characterization of its metabolite profile. Several temperatures (12, 16, 20, 25, 30°C), L1 nutrient concentrations (0.5×, 2×, 2.5×, 3×) and NaCl concentrations (20, 25, 30, 40 g L^-1 ) were tested. The growth rate was maximum at 16°C, 2× nutrient concentration and 40 g L^-1 of NaCl; hence, these conditions were chosen for bulk production of biomass. Methanolic extracts were prepared, and pigments, lipids and phenolic compounds were assessed; complemented by antioxidant and anti-inflammatory capacities, and cytotoxicity. Fucoxanthin and derivatives accounted for 0.06% of dry weight, and up to 60% (w/w) of all quantified metabolites were lipids. Said extracts displayed high antioxidant capacity, as towards assessed via the NO^•- and ABTS^•+ assays (IC₅₀  = 109.09 ± 6.73 and 266.46 ± 2.25 µg_E  ml^-1 , respectively), unlike observed via the O₂ ^•- assay (IC₂₅ reaching 56.06 ± 5.56 µg_E  ml^-1 ). No signs of cytotoxicity were observed.

CONCLUSIONS

Karlodinium veneficum biomass production was consistently optimized in terms of temperature, L1 nutrient concentrations and NaCl concentration. In addition, this strain appears promising for eventual biotechnological exploitation.

SIGNIFICANCE AND IMPACT OF THE STUDY

This work provides fundamental insights about the growth and potential of value-added compounds of dinoflagellate K. veneficum. Dinoflagellates, as K. veneficum are poorly studied regarding its biomass production and added-value compounds for potential biotechnological exploitation. These organisms are difficult to maintain and grow in the laboratory. Thus, any fundamental contribution is relevant to share with the scientific community.

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.

Influence of seasonality on the presence of okadaic acid associated with Dinophysis species: A four-year study in Sardinia (Italy)

In Sardinia (Italy), bivalve molluscs production plays an important role in the trade balance. Diarrhoetic shellfish poisoning (DSP), an intoxication caused by the ingestion of bivalve molluscs that have accumulated high levels of Okadaic acid (OA), may represent a serious risk for the public health and a remarkable economic loss for the producers. Aim of this work was to improve knowledge about the repeatability of OA accumulation phenomena in various seasons trying to understand whether or not there was a trend. Also, the interaction between toxic algae and OA accumulation was examined. In this study, data of lipophilic toxins, water temperature and abundance of DSP-producing microalgal species were collected in a four-year period (2015–2018) in coastal production areas of Sardinia. Several episodes of OA positive values (>160 eq μgAO/Kg pe, Reg 853/04) were recorded during the study period in different production areas of Sardinia and in different seasons. A seasonal repeatability of OA accumulation in molluscs was observed in some production areas; moreover, different temporal gaps between the presence of toxic algae and OA accumulation were reported. Toxicity was observed almost exclusively in Mytilus galloprovincialis Lamark (99%), being this matrix the most abundant species bred in Sardinia.

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.

Future HAB science: Directions and challenges in a changing climate

There is increasing concern that accelerating environmental change attributed to human-induced warming of the planet may substantially alter the patterns, distribution and intensity of Harmful Algal Blooms (HABs). Changes in temperature, ocean acidification, precipitation, nutrient stress or availability, and the physical structure of the water column all influence the productivity, composition, and global range of phytoplankton assemblages, but large uncertainty remains about how integration of these climate drivers might shape future HABs. Presented here are the collective deliberations from a symposium on HABs and climate change where the research challenges to understanding potential linkages between HABs and climate were considered, along with new research directions to better define these linkages. In addition to the likely effects of physical (temperature, salinity, stratification, light, changing storm intensity), chemical (nutrients, ocean acidification), and biological (grazer) drivers on microalgae (senso lato), symposium participants explored more broadly the subjects of cyanobacterial HABs, benthic HABs, HAB effects on fisheries, HAB modelling challenges, and the contributions that molecular approaches can bring to HAB studies. There was consensus that alongside traditional research, HAB scientists must set new courses of research and practices to deliver the conceptual and quantitative advances required to forecast future HAB trends. These different practices encompass laboratory and field studies, long-term observational programs, retrospectives, as well as the study of socioeconomic drivers and linkages with aquaculture and fisheries. In anticipation of growing HAB problems, research on potential mitigation strategies should be a priority. It is recommended that a substantial portion of HAB research among laboratories be directed collectively at a small sub-set of HAB species and questions in order to fast-track advances in our understanding. Climate-driven changes in coastal oceanographic and ecological systems are becoming substantial, in some cases exacerbated by localized human activities. That, combined with the slow pace of decreasing global carbon emissions, signals the urgency for HAB scientists to accelerate efforts across disciplines to provide society with the necessary insights regarding future HAB trends.

Variability of dinoflagellates and their associated toxins in relation with environmental drivers in Ambon Bay, eastern Indonesia

The aim of the present work was to unravel which environmental drivers govern the dynamics of toxic dinoflagellate abundance as well as their associated paralytic shellfish toxins (PSTs), diarrhetic shellfish toxins (DSTs) and pectenotoxin-2 (PTX2) in Ambon Bay, Eastern Indonesia. Weather, biological and physicochemical parameters were investigated weekly over a 7-month period. Both PSTs and PTX2 were detected at low levels, yet they persisted throughout the research. Meanwhile, DSTs were absent. A strong correlation was found between total particulate PST and Gymnodinium catenatum cell abundance, implying that this species was the main producer of this toxin. PTX2 was positively correlated with Dinophysis miles cell abundance. Vertical mixing, tidal elevation and irradiance attenuation were the main environmental factors that regulated both toxins and cell abundances, while nutrients showed only weak correlations. The present study indicates that dinoflagellate toxins form a potential environmental, economic and health risk in this Eastern Indonesian bay.

Distribution Characteristics and Environmental Control Factors of Lipophilic Marine Algal Toxins in Changjiang Estuary and the Adjacent East China Sea

Marine algal toxins, highly toxic secondary metabolites, have significant influences on coastal ecosystem health and mariculture safety. The occurrence and environmental control factors of lipophilic marine algal toxins (LMATs) in the surface seawater of the Changjiang estuary (CJE) and the adjacent East China Sea (ECS) were investigated. Pectenotoxin-2 (PTX2), okadaic acid (OA), dinophysistoxin-1(DTX1), and gymnodimine (GYM) were detected in the CJE surface seawater in summer, with concentration ranges of not detected (ND)-105.54 ng/L, ND-13.24 ng/L, ND-5.48 ng/L, and ND-12.95 ng/L, respectively. DTX1 (ND-316.15 ng/L), OA (ND-16.13 ng/L), and PTX2 (ND-4.97 ng/L) were detected in the ECS during spring. LMATs formed a unique low-concentration band in the Changjiang diluted water (CJDW) coverage area in the typical large river estuary. PTX2, OA, and DTX1 in seawater were mainly derived from Dinophysis caudate and Dinophysis rotundata, while GYM was suspected to be from Karenia selliformis. Correlation analyses showed that LMAT levels in seawater were positively correlated with dissolved oxygen and salinity, but negatively correlated with temperature and nutrients, indicating that the hydrological condition and nutritional status of seawater and climatic factors exert significant effects on the distribution of LMATs.

Role of temperature and nutrients on the growth and toxin production of Prorocentrum hoffmannianum (Dinophyceae) from the Florida Keys

The benthic dinoflagellate Prorocentrum hoffmannianum M.A. Faust is typical of tropical warm waters and produces biotoxins responsible for diarrhetic shellfish poisoning (DSP). In this study, the effect of temperature and nutrient limitation on growth and toxin production of P. hoffmannianum isolated from field samples collected in the Florida Keys was investigated. Batch culture experiments were ran at two temperatures (i.e. 21 ± 0.1 and 27 ± 0.1 °C) and under nitrogen-limited (14.7 μmol L^-1 N-NO₃- and 18.1 μmol L^-1 P-PO₄^3-) and phosphorus-limited (441 μmol L^-1 N-NO₃- and 0.6 μmol L^-1 P-PO₄^3-) levels with respect to control nutrient conditions (441 μmol L^-1 N-NO₃-and 18.1 μmol L^-1 P-PO₄^3-). Both temperature and nutrient conditions significantly affected growth rates and maximum yield of P. hoffmannianum with the maximum values being recorded at the higher temperature and in the replete medium. Production of okadaic acid was induced under all conditions (from 13.5 to 859.8 pg cell^-1), with values up to one order of magnitude higher than those observed in other DSP toxin producing species. Toxin production was enhanced under P limitation at 27 °C, corroborating the theory that toxin production is modulated by cell physiological conditions, which are in turn affected by a wide spectrum of factors, including environmental stressors such as nutrient availability. Toxin fraction released in the growth medium was negligible. No okadaic acid esters were detected in this strain of P. hoffmannianum.

Toxin Profiles of Okadaic Acid Analogues and Other Lipophilic Toxins in Dinophysis from Japanese Coastal Waters

The identification and quantification of okadaic acid (OA)/dinophysistoxin (DTX) analogues and pectenotoxins (PTXs) in Dinophysis samples collected from coastal locations around Japan were evaluated by liquid chromatography mass spectrometry. The species identified and analyzed included Dinophysis fortii, D. acuminata, D. mitra (Phalacroma mitra), D. norvegica, D. infundibulus, D. tripos, D. caudata, D. rotundata (Phalacroma rotundatum), and D. rudgei. The dominant toxin found in D. acuminata was PTX2 although some samples contained DTX1 as a minor toxin. D. acuminata specimens isolated from the southwestern regions (Takada and Hiroshima) showed characteristic toxin profiles, with only OA detected in samples collected from Takada. In contrast, both OA and DTX1, in addition to a larger proportion of PTX2, were detected in D. acuminata from Hiroshima. D. fortii showed a toxin profile dominated by PTX2 although this species had higher levels of DTX1 than D. acuminata. OA was detected as a minor toxin in some D. fortii samples collected from Yakumo, Noheji, and Hakata. PTX2 was also the dominant toxin found among other Dinophysis species analyzed, such as D. norvegica, D. tripos, and D. caudata, although some pooled picked cells of these species contained trace levels of OA or DTX1. The results obtained in this study re-confirm that cellular toxin content and profiles are different even among strains of the same species.

Diarrhetic Shellfish Toxin Monitoring in Commercial Wild Harvest Bivalve Shellfish in New South Wales, Australia

An end-product market survey on biotoxins in commercial wild harvest shellfish (Plebidonax deltoides, Katelysia spp., Anadara granosa, Notocallista kingii) during three harvest seasons (2015⁻2017) from the coast of New South Wales, Australia found 99.38% of samples were within regulatory limits. Diarrhetic shellfish toxins (DSTs) were present in 34.27% of 321 samples but only in pipis (P. deltoides), with two samples above the regulatory limit. Comparison of these market survey data to samples (phytoplankton in water and biotoxins in shellfish tissue) collected during the same period at wild harvest beaches demonstrated that, while elevated concentrations of Dinophysis were detected, a lag in detecting bloom events on two occasions meant that wild harvest shellfish with DSTs above the regulatory limit entered the marketplace. Concurrently, data (phytoplankton and biotoxin) from Sydney rock oyster (Saccostrea glomerata) harvest areas in estuaries adjacent to wild harvest beaches impacted by DSTs frequently showed elevated Dinophysis concentrations, but DSTs were not detected in oyster samples. These results highlighted a need for distinct management strategies for different shellfish species, particularly during Dinophysis bloom events. DSTs above the regulatory limit in pipis sampled from the marketplace suggested there is merit in looking at options to strengthen the current wild harvest biotoxin management strategies.

Interannual variability in Dinophysis spp. abundance and toxin accumulation in farmed mussels (Perna perna) in a subtropical estuary

This study evaluated an 8-year dataset (2007 to 2015, except 2008) in the attempt to identify the most susceptible periods for the occurrence of diarrheic shellfish poisoning (DSP) episodes associated with the presence of toxigenic dinoflagellates, Dinophysis spp., in the mussel farming area of Babitonga Bay (southern Brazil). Dinophysis acuminata complex was the most frequent (present in 66% of the samples) and abundant (max. 4100 cells L^-1) taxon, followed by D. caudata (14%; max. 640 cells L^-1) and D. tripos (0.9%; max. 50 cells L^-1). There was a marked onset of the annual rise in Dinophysis spp. abundance during weeks 21-25 (early winter) of each year, followed by a second peak on week 35 (spring). Mussel (Perna perna) samples usually started testing positive in DSP mouse bioassays (MBA) in late winter. Positive results were more frequent in 2007 and 2011 when the mean D. acuminata complex abundance was ~ 500 cells L^-1. Although positive DSP-MBA results were observed in only 11% of the samples during the studied period, the toxin okadaic acid (OA) was present in 90% of the analyzed mussels (max. 264 μg kg^-1). MBA results were positive when D. acuminata complex cell densities exceed 1200 ± 300 cells L^-1, while trace toxin amounts could be detected at cell densities as low as 150 ± 50 cells L^-1 (free OA) to 200 ± 100 cells L^-1 (conjugated OA). Low salinity and the meteorological conditions triggered by La Niña events were the main factors associated with both Dinophysis abundance and OA accumulation in mussels.

Thermal acclimation affects growth and lipophilic toxin production in a strain of cosmopolitan harmful alga Dinophysis acuminata

Species of the harmful algal bloom (HAB) genera Dinophysis are causative of one of the most widespread and expanding HAB events associated with the human intoxication, diarrheic shellfish poisoning (DSP). The effects of warming temperature on the physiology and toxinology of these mixotrophic species remain intractable due to their low biomass in nature and difficulties in establishing and maintaining them in culture. Hence, the present study investigated the influence of warming temperature, encompassing present and predicted climate scenarios, on growth and toxin production in a strain of the most cosmopolitan DSP-causative species, Dinophysis acuminata. The strain was isolated from western Japan, acclimated, and cultured over extended time spans. The specific growth and toxin production rates were highest at 20-26 °C and 17-29 °C, respectively, and had significant linear relationships during exponential phase. The cellular toxin production of okadaic acid and pectenotoxin-2 were highest during early exponential growth phase at temperatures ≤17 °C but highest during late stationary phase at temperatures ≥20 °C. The cellular toxin production of Dinophysistoxin-1, however, increased from early exponential to late stationary growth phase independently from temperature. The net toxin productions were not affected by acclimation temperature but significantly affected by growth and were highest during early exponential growth phase. Warming water temperatures increase growth and promote toxin production of D. acuminata, potentially increasing incidence of diarrheic shellfish poisoning events and closures of shellfish production. It is likely that D. acuminata is more toxic at low cell densities during bloom initiation in winter, and at high cell densities during bloom termination in spring-autumn. The results of the present research are also of importance for the mass production of D. acuminata for subsequent studies of the toxicological and pharmacological bioactivities of DSTs and PTX2, and the fate of these toxins in the natural environment and the vectoring shellfish molluscs.

Effects of copper and butyltin compounds on the growth, photosynthetic activity and toxin production of two HAB dinoflagellates: The planktonic Alexandrium catenella and the benthic Ostreopsis cf. ovata

Controlled laboratory experiments were conducted to test the effects of copper (Cu²⁺) and butyltins (BuT) on the growth, photosynthetic activity and toxin content of two HABs (Harmful Algal Blooms) dinoflagellates, the planktonic Alexandrium catenella and the benthic Ostreopsis cf. ovata. Microalgae were exposed to increasing concentrations of Cu²⁺ (10^-4 to 31 nM) or BuT (0.084 to 84 nM) for seven days. When considering the growth, EC₅₀ values were 0.16 (±0.09) nM and 0.03 (±0.02) nM of Cu²⁺ for A. catenella and O. cf. ovata, respectively. Regarding BuT, EC₅₀ was 14.2 (±6) nM for O. cf. ovata, while A. catenella growth inhibition appeared at BuT concentrations ≥27 nM. Photosynthetic activity of the studied dinoflagellates decreased with increasing Cu and BuT concentrations. For O. cf. ovata, the response of this physiological parameter to contamination was less sensitive than the biomass. Cu exposure induced the formation of temporary cysts in both organisms that could resist adverse conditions. The ovatoxin-a and -b concentrations in O. cf. ovata cells increased significantly in the presence of Cu. Altogether, the results suggest a better tolerance of the planktonic A. catenella to Cu and BuT. This could result in a differentiated selection pressure exerted by these metals on phytoplankton species in highly polluted waters. The over-production of toxins in response to Cu stress could pose supplementary health and socio-economic threats in the contaminated marine ecosystems where HABs develop.