Domoic Acid Concentrations Research Articles

A Time Series of Water Column Distributions and Sinking Particle Flux of Pseudo-Nitzschia and Domoic Acid in the Santa Barbara Basin, California.

Water column bulk Pseudo-nitzschia abundance and the dissolved and particulate domoic acid (DA) concentrations were measured in the Santa Barbara Basin (SBB), California from 2009–2013 and compared to bulk Pseudo-nitzschia cell abundance and DA concentrations and fluxes in sediment traps moored at 147 m and 509 m. Pseudo-nitzschia abundance throughout the study period was spatially and temporally heterogeneous (<200 cells L−1 to 3.8 × 106 cells L−1, avg. 2 × 105 ± 5 × 105 cells L−1) and did not correspond with upwelling conditions or the total DA (tDA) concentration, which was also spatially and temporally diverse (<1.3 ng L−1 to 2.2 × 105 ng L−1, avg. 7.8 × 103 ± 2.2 × 104 ng L−1). We hypothesize that the toxicity is likely driven in part by specific Pseudo-nitzschia species as well as bloom stage. Dissolved (dDA) and particulate (pDA) DA were significantly and positively correlated (p < 0.01) and both comprised major components of the total DA pool (pDA = 57 ± 35%, and dDA = 42 ± 35%) with substantial water column concentrations (>1000 cells L−1 and tDA = 200 ng L−1) measured as deep as 150 m. Our results highlight that dDA should not be ignored when examining bloom toxicity. Although water column abundance and pDA concentrations were poorly correlated with sediment trap Pseudo-nitzschia abundance and fluxes, DA toxicity is likely associated with senescent blooms that rapidly sink to the seafloor, adding another potential source of DA to benthic organisms.

Evaluation of intracellular and extracellular domoic acid content in Pseudo-nitzschia multiseries cell cultures under different light regimes

Pseudo-nitzschia multiseries is a diatom species associated with the production of domoic acid (DA), a water soluble neurotoxin that is easily transferred up in the food web, causing devastating effects on top marine organisms and humans. Despite studies on Pseudo-nitzschia are relevant to human health safety, partitioning of marine toxins between intracellular and extracellular fractions are poorly documented. This study aimed to determine the growth rates and DA content, both intracellular and extracellular, of Pseudo-nitzschia multiseries cultures at three different light settings (15, 120 and 560 μmol m−2 s−1). The optimal conditions for cell growth were observed at 120 and 560 μmol m−2 s−1, whereas DA production was observed in P. multiseries at 15 and 120 μmol m−2 s−1, ranging between 0.18-2.56 and 0.16–3.5 pg DA cell−1, respectively. Higher intracellular DA concentrations were found during the senescence phase at low light intensity and during the exponential phase at medium light intensity, while higher concentrations of dissolved DA were found at low and medium light intensities in the senescence phase reaching 3 and 10 ng DA mL−1 respectively. The amount of toxin released into the culture medium represents the most important fraction ranging between 63 and 98% during the exponential phase and nearly 99% during the senescence phase. In contrast, under low light intensity, dissolved DA was detected in the culture medium only during the senescence phase. This study confirms the importance of light intensity on DA production and clearly shows that dissolved domoic acid is an important fraction in Pseudo-nitzschia cultures, suggesting with the careful assumptions of results from static cultures extrapolated to bloom situations that waterborne exposure of marine organism should be considered during blooms of Pseudo-nitzschia multiseries.

Validated HPLC-MS/MS Method To Quantify Low Levels of Domoic Acid in Plasma and Urine after Subacute Exposure.

Domoic acid (DA) is a marine neurotoxin produced by several species of Pseudo-nitzschia. DA causes severe neurological toxicity in humans and animals. To address the current analytical need to quantify low levels of DA in human and animal body fluids, a sensitive and selective high performance liquid chromatography-tandem mass spectrometry method was developed to measure DA in plasma and urine. This method was fully validated to accurately and precisely quantify DA between 0.31 and 16 ng/mL in plasma and between 7.8 and 1000 ng/mL in urine. Our group introduced the use of a novel internal standard, tetrahydrodomoic acid to control for matrix effects and other sources of variability. This validated method will be useful to assess DA concentrations in biological samples of human or animal origin after suspected DA exposure from contaminated food. It will also be applicable to sentinel programs and research studies to analyze body fluids with low levels of DA.

Pseudo-nitzschia sp. diversity and seasonality in the southern North Sea, domoic acid levels and associated phytoplankton communities

The diversity, toxicity and seasonality of Pseudo-nitzschia sp. were investigated from February to November 2012 in the southern Bight of the North Sea (SBNS) along the French coast. The identification of Pseudo-nitzschia species in this area was addressed for the first time in this study. Our results revealed a low species richness (3 distinct species) in association with moderate (102 pg mL−1) to high (263 pg mL−1) domoic acid (DA) levels in autumn and spring, respectively.Pseudo-nitzschia succession corresponded to the dominance of P. delicatissima in April–May (86% of total diatoms) as a co-occurring species of the Phaeocystis globosa bloom. Following the Phaeocystis bloom (May–September), P. pungens dominated markedly over P. fraudulenta and P. delicatissima and was the only species present in autumn, although at low abundance (<1000 cell L−1). The results of this study support the idea that Pseudo-nitzschia seasonality in the SBNS relies principally on temperature and nutrient availability (DIN and silicates), which, in turn, depend on locally fluctuating environmental conditions (rainfalls and winds). This study highlights the potential for the SBNS to be a potential risk area in regard to the possible impacts of DA on marine resources and the DA transfer through marine food webs. This is of particular concern since DA concentration in seawater was not systematically correlated to potentially toxic Pseudo-nitzschia abundance.

Domoic Acid-Producing Diatoms of the Genus Pseudo-nitzschia H. Peragallo, 1900 (Bacillariophyta) from the North Pacific

Information on diatoms of the genus Pseudo-nitzschia, known as producers of domoic acid (DA), from the North Pacific is summarized. The differences in the negative impact of toxic diatoms on ecosystems in the western and eastern North Pacific are shown. The possible causes that determine the degree of these different impacts are discussed: a different composition of dominant species; a difference in the intracellular DA concentration in bloom-forming species; the hydrological, climatic, and hydrochemical factors that are responsible for the formation of toxic blooms (upwelling events, patterns of water circulation, concentration of iron compounds in sea water, etc.). The conclusion is made that the prospects of further studies of toxic diatoms are based on comparative investigations into the species and genetic diversity of Pseudo-nitzschia and associated bacteria, as well as the environmental parameters that control the formation of toxic blooms and the accumulation of DA in microalgae and other marine organisms in the eastern and western North Pacific.

A decade and a half of Pseudo-nitzschia spp. and domoic acid along the coast of southern California

Blooms of the marine diatom genus Pseudo-nitzschia that produce the neurotoxin domoic acid have been documented with regularity along the coast of southern California since 2003, with the occurrence of the toxin in shellfish tissue predating information on domoic acid in the particulate fraction in this region. Domoic acid concentrations in the phytoplankton inhabiting waters off southern California during 2003, 2006, 2007, 2011 and 2017 were comparable to some of the highest values that have been recorded in the literature. Blooms of Pseudo-nitzschia have exhibited strong seasonality, with toxin appearing predominantly in the spring. Year-to-year variability of particulate toxin has been considerable, and observations during 2003, 2006, 2007, 2011 and again in 2017 linked domoic acid in the diets of marine mammals and seabirds to mass mortality events among these animals. This work reviews information collected during the past 15 years documenting the phenology and magnitude of Pseudo-nitzschia abundances and domoic acid within the Southern California Bight. The general oceanographic factors leading to blooms of Pseudo-nitzschia and outbreaks of domoic acid in this region are clear, but subtle factors controlling spatial and interannual variability in bloom magnitude and toxin production remain elusive.

Long-term neurotoxic effects of domoic acid on primary dopaminergic neurons

Domoic acid, an excitatory neurotoxin produced by certain algae, reaches the food chain through accumulation in some sea organisms. To investigate its long-term neurotoxicity on dopaminergic neurons, prepared primary mesencephalic cell cultures were exposed to different concentrations of domoic acid (0.1, 1, 10, 100 μM) on the 8th day in vitro (DIV) for 4 days. On the 12th DIV, culture media were collected for measurement of lactate dehydrogenase and cultured cells were subjected to immunohistochemistry against tyrosine hydroxylase, neuronal nuclear antigen and glial fibrillary acidic protein, and fluorescence staining using H2DCFDA, JC-1 and Hoechst 33342 dyes. Moreover, roles of AMPA/KA and NMDA receptors in domoic acid neurotoxicity were also investigated. Domoic acid significantly decreased the number of dopaminergic neurons and adversely affected their morphology, and slightly reduced the expression of neuronal nuclear antigen and glial fibrillary acidic protein. Co-treatment of cultures with domoic acid and the AMPA/KA or NMDA receptor antagonists NBQX and MK-801 rescued significant number of dopaminergic neurons. Domoic acid significantly decreased red:green fluorescence ratio of JC-1 and did not affect production of reactive oxygen species and apoptotic cell death. In conclusions, the present study reveals that long-term treatment of primary mesencephalic cell culture with domoic acid significantly destroyed dopaminergic neurons. This effect appears to be attributed to activation of AMPA/KA and NMDA receptors and mitochondrial damage.

Induction of domoic acid production in diatoms—Types of grazers and diatoms are important

Grazers can induce toxin (domoic acid, DA) production in diatoms. The toxic response has been observed in two species of Pseudo-nitzschia and was induced by Calanus copepods. In this study, interactions between diatoms and copepods were further explored using different species of diatoms and copepods. All herbivorous copepods induced toxin production, whereas exposure to carnivorous copepods did not. In line with this, increasing the number of herbivorous copepods resulted in even higher toxin production. The induced response is thus only elicited by copepods that pose a real threat to the responding cells, which supports that the induced toxin production in diatoms evolved as an inducible defense.The cellular toxin content in Pseudo-nitzschia was positively correlated to the concentration of a group of specific polar lipids called copepodamides that are excreted by the copepods. This suggests that copepodamides are the chemical cues responsible for triggering the toxin production. Carnivorous copepods were found to produce less or no copepodamides.Among the diatoms exposed to grazing herbivorous copepods, only two of six species of Pseudo-nitzschia and none of the Nitzschia or Fragilariopsis strains responded by producing DA, indicating that not all Pseudo-nitzschia species/strains are able to produce DA, and that different diatom species might have different strategies for coping with grazing pressure. Growth rate was negatively correlated to cellular domoic acid content indicating an allocation cost associated with toxin production. Long-term grazing experiments showed higher mortality rates of grazers fed toxic diatoms, supporting the hypothesis that DA production is an induced defense mechanism.

Maternal‐Fetal Toxicokinetics of the Shellfish Toxin Domoic Acid

BackgroundDomoic Acid (DA) is an excitatory neurotoxin produced by harmful algal blooms. Through the marine food web, humans and marine mammals can be exposed to DA and experience DA poisoning. To protect humans, a tolerable daily intake (TDI) of 0.075 mg/kg of DA has been suggested based on acute/short term exposure “no observable adverse effect level” (NOAEL) in animals with a 10‐fold safety factor. However, several studies in model species have suggested that chronic DA exposure at subacute level is also harmful to the central nervous system. Similarly, it has been suggested that in utero exposure to DA adversely affects fetal neurological development which highlights the need to establish safe chronic consumption levels in vulnerable populations. The purpose of this study was to characterize DA disposition during pregnancy following chronic subacute dosing, and to determine whether such chronic DA exposure results in significant fetal exposures and alters infant behavioral outcomes in cynomolgus monkeys.MethodFemale monkeys (n=10) were orally dosed daily with 0.15 mg/kg DA for at least two months prior to and over the course of pregnancy. DA pharmacokinetics were characterized pre‐pregnancy, and on weeks 9 and 17 of gestation. At delivery, the maternal plasma and amniotic fluid DA concentrations were measured. Infant plasma DA concentrations were measured from birth to day 7 and neonatal behavioral outcomes were measured from birth to day 14. Maternal‐fetal pharmacokinetics of DA through pregnancy was simulated using physiologically‐based pharmacokinetic (PBPK) modeling.ResultsThe renal clearance of DA was significantly increased in these monkeys in parallel with increased GFR during pregnancy, but the overall exposure to DA was similar during pregnancy as before pregnancy (Table 1). Average maternal plasma, fetal plasma, and amniotic fluid concentrations at time of delivery were 2.1 ± 1.3 ng/mL (n=9), 1.3 ± 1.0 ng/mL (n=8), and 7.5 ± 5.0 ng/mL (n=5), respectively. Fetal to maternal plasma and amniotic fluid to maternal plasma concentration ratios were 0.6 (95% CI: 0.4, 1.0) and 3.5 (95% CI: 1.8, 7.1). Results from behavioral testing of the infants suggested that in utero exposure to DA at subacute dose levels may be associated with adverse effects on neurocognitive development.ConclusionThe results of this study suggest that mother and fetus exposures are nearly similar following repeated doses of DA during pregnancy. The high amniotic fluid to maternal concentration ratio suggests that amniotic fluid acts as a “deep compartment” of fetal distribution, and may contribute to continuous fetal exposure in utero. Collectively the data suggest that the TDI estimates for DA may need to be lowered to assure maternal‐fetal safety.Support or Funding InformationR01 ES023043‐01 NIH/NIEHSThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

A Bayesian Semiparametric Regression Model for Joint Analysis of Microbiome Data.

The successional dynamics of microbial communities are influenced by the synergistic interactions of physical and biological factors. In our motivating data, ocean microbiome samples were collected from the Santa Cruz Municipal Wharf, Monterey Bay at multiple time points and then 16S ribosomal RNA (rRNA) sequenced. We develop a Bayesian semiparametric regression model to investigate how microbial abundance and succession change with covarying physical and biological factors including algal bloom and domoic acid concentration level using 16S rRNA sequencing data. A generalized linear regression model is built using the Laplace prior, a sparse inducing prior, to improve estimation of covariate effects on mean abundances of microbial species represented by operational taxonomic units (OTUs). A nonparametric prior model is used to facilitate borrowing strength across OTUs, across samples and across time points. It flexibly estimates baseline mean abundances of OTUs and provides the basis for improved quantification of covariate effects. The proposed method does not require prior normalization of OTU counts to adjust differences in sample total counts. Instead, the normalization and estimation of covariate effects on OTU abundance are simultaneously carried out for joint analysis of all OTUs. Using simulation studies and a real data analysis, we demonstrate improved inference compared to an existing method.

Differential toxin response of Pseudo-nitzschia multiseries as a function of nitrogen speciation in batch and continuous cultures, and during a natural assemblage experiment

The toxigenic diatom Pseudo-nitzschia multiseries Hasle, isolated from the U.S. Pacific Northwest, was examined in unialgal laboratory cultures and in natural assemblages during shipboard experiments, to examine cellular growth and domoic acid (DA) production as a function of nitrogen (N) substrate and availability expected during bloom development and decline. Laboratory experiments utilizing batch cultures conducted at saturating (120 μmol photons m−2 s−1) photosynthetic photon flux density (PPFD), demonstrated that P. multiseries (strain NWFSC-245) grows equally well on the three N substrates tested (nitrate [NO3−], ammonium [NH4+] and urea), and achieved an average specific growth rate of 0.83 d−1. Despite equivalent growth rates, cellular toxicity (particulate DA concentration normalized to cell abundance) varied as a function of N substrate, with urea-grown cells demonstrating 1.3- and 3.4-fold more toxicity than both NH4+- and NO3−-grown cells. Cellular toxicity of the N-limited chemostat cultures, grown at a dilution rate of 0.48 d−1, were less than the cellular toxicity measured for the N-replete batch cultures for all three N substrates, but again cellular toxicity varied as a function of N substrate and the urea-supported cells were 3.5- and 4.3-fold more toxic than the respective NH4+- and NO3−-supported cells. Starved cultures of P. multiseries showed no decline in cellular toxicity or change in the order of toxicity as a function of N substrate, and cells previously supported by urea were 13- and 5-fold more toxic than NH4+- and NO3−-supported cells. At all three levels of N-sufficiency, the urea-grown cells consistently produced the highest concentration of particulate DA per cell compared to cells grown on either NO3− or NH4+.Shipboard N enrichment experiments using natural phytoplankton assemblages were conducted off the west coast of Washington in an area characterized by elevated concentrations of macronutrients and iron. All N (NO3−, NH4+ and urea) treatments showed significant increases in biomass (as measured by total and size-fractionated chlorophyll a) and the abundance of Pseudo-nitzschia species over the 6-d experiment. As with the unialgal laboratory experiments, cellular toxicity varied as a function of the N source supporting growth, and the planktonic assemblages enriched with either NH4+ or urea demonstrated greater cellular toxicity than the assemblages supported solely by NO3−. These laboratory and field results demonstrate that N substrate can regulate the toxicity of Pseudo-nitzschia species, and that N source should be considered when evaluating the potential effects of cultural eutrophication on the growth of toxigenic diatoms.

Determination of Domoic Acid in Plankton Net Samples from Golden Horn Estuary, Turkey, Using HPLC with Fluorescence Detection.

This study focused on the fluctuations of domoic acid (DA) levels in plankton net samples collected from the Golden Horn Estuary (GHE), Turkey, between August 2011 and July 2012. DA concentrations were determined by high-performance liquid chromatography (HPLC), using a fluorenylmethoxycarbonyl (FMOC) derivatization technique. Monthly and biweekly data were evaluated with environmental variables, and their influence on DA production is discussed. DA levels in plankton net samples varied between 0.36 and 94.34µgL- 1. DA levels showed remarkable seasonal variation and they were generally higher in May, 2012, but no DA was detected between February and April, 2012. DA production was mostly controlled by temperature, with nitrate and silicate limitations being secondary factors that influenced DA concentrations.

Neurotoxic effects of domoic acid on dopaminergic neurons in primary mesencephalic cell culture.

Domoic acid is a potent marine neurotoxin produced by certain species of the diatom genus Pseudonitzschia. To our knowledge, there are no studies that have investigated neurotoxic effects of domoic acid on dopaminergic neurons. Accordingly, the present study was carried out to investigate the potential neurotoxic effects of domoic acid on dopaminergic neurons in primary mesencephalic cell culture. Cultures prepared from embryonic mouse mesencephala (total of 250 embryos) were treated with different concentrations of domoic acid (0.1, 1, 10, 100 µM) on the 10th DIV for 48 h. On the 12th DIV, culture media were used for measurement of lactate dehydrogenase and cultured cells were subjected to immunostaining for tyrosine hydroxylase, neuronal nuclear antigen and glial fibrillary acidic protein, and fluorescence staining using H2DCFDA, JC-1 and DAPI stains. Moreover, roles of AMPA/KA and NMDA receptors in domoic acid neurotoxicity were also investigated. Domoic acid significantly decreased the number of dopaminergic neurons, decreased the expression of neuronal nuclear antigen and slightly affected astrocyte populations, and increased the release of lactate dehydrogenase into the culture media. AMPA/KA receptor antagonist NBQX but not NMDA receptor antagonist MK-801 significantly inhibited the neurotoxic effect of domoic acid on dopaminergic neurons. H<SUB>2</SUB>DCFDA, JC-1 and DAPI fluorescence staining, respectively, revealed that DomA slightly raised ROS production, and significantly decreased mitochondrial membrane potential and increased apoptotic cell death of cultured cells. The current study presents for the first time the neurotoxic effects of domoic acid on dopaminergic neurons and this effect appears to be attributed to activation of AMPA/KA receptors on dopaminergic neurons.

Pseudo-nitzschia species composition varies concurrently with domoic acid concentrations during two different bloom events in the Southern California Bight

The San Pedro Shelf (SPS) region of the Southern California Bight has witnessed an increase of Pseudo-nitzschia spp. blooms during the past decade, although the domoic acid (DA) concentrations observed during these events have varied considerably. This study compared the extent, timing and environmental controls of Pseudo-nitzschia blooms that were observed in two consecutive years on the SPS. Environmental conditions were characterized during shipboard surveys during spring 2013 and 2014 along an onshore–offshore transect at surface and subsurface depths. A Pseudo-nitzschia bloom of similar cell abundances was observed during each year, yet maximal DA concentrations differed by nearly two orders of magnitude. Environmental parameters were favorable for Pseudo-nitzschia spp. growth in both years, but few factors could be identified that specifically pertained to DA, with the exception that toxicity correlated negatively with dissolved silicic acid concentrations. Automated ribosomal intergenic spacer analysis for Pseudo-nitzschia species indicated that the relative abundance of toxin-producing species had a strong influence on DA concentrations between years, with high-DA concentrations corresponding to Pseudo-nitzschia communities dominated by P. australis/P. seriata. Factors explaining the preferential growth of particular Pseudo-nitzschia species remain enigmatic but are important for predicting toxic events attributable to these taxa.

Growth, Toxin Production and Allelopathic Effects of Pseudo-nitzschia multiseries under Iron-Enriched Conditions.

In order to assess the effects of Fe-enrichment on the growth and domoic acid (DA) production of the toxigenic diatom Pseudo-nitzschia multiseries, static cultures that received the addition of different iron (Fe) concentrations were maintained for 30 days. Intra- and extracellular DA concentrations were evaluated over time, and growth and chain-formation were compared to those of non-toxic diatoms, Bacillaria sp. Growth rates of P. multiseries (μ = 0.45–0.73 d−1) were similar among cultures containing different Fe concentrations. Likewise, the similar incidence and length of P. multiseries stepped cell chains (usually 2–4; up to 8-cell long) among the treatments reinforces that the cultures were not growth-inhibited under any condition tested, suggesting an efficient Fe acquisition mechanism. Moreover, DA concentrations were significantly higher under the highest Fe concentration, indicating that Fe is required for toxin synthesis. Bacillaria sp. reached comparable growth rates under the same Fe concentrations, except when the dissolved cell contents from a P. multiseries culture was added. The 50–70% reduction in cell density and 70–90% decrease in total chlorophyll-a content of Bacillaria sp. at early stationary growth phase indicates, for the first time, an allelopathic effect of undetermined compounds released by Pseudo-nitzschia to another diatom species.

Nutrient ratios influence variability in Pseudo-nitzschia species diversity and particulate domoic acid production in the Bay of Seine (France)

The population dynamics of different Pseudo-nitzschia species, along with particulate domoic acid (pDA) concentrations, were studied from May 2012 to December 2013 in the Bay of Seine (English Channel, Normandy). While Pseudo-nitzschia spp. blooms occurred during the two years of study, Pseudo-nitzschia species diversity and particulate domoic acid concentrations varied greatly. In 2012, three different species were identified during the spring bloom (P. australis, P. pungens and P. fraudulenta) with high pDA concentrations (∼1400ngl−1) resulting in shellfish harvesting closures. In contrast, the 2013 spring was characterised by a P. delicatissima bloom without any toxic event. Above all, the results show that high pDA concentrations coincided with the presence of P. australis and with potential silicate limitation (Si:N<1), while nitrate concentrations were still replete. The contrasting environmental conditions between 2012 and 2013 highlight different environmental controls that might favour the development of either P. delicatissima or P. australis. This study points to the key role of Pseudo-nitzschia diversity and cellular toxicity in the control of particulate domoic acid variations and highlights the fact that diversity and toxicity are influenced by nutrients, especially nutrient ratios.

Taxonomical diversity of Pseudo‐nitzschia from the Central Adriatic Sea

SUMMARYThe aim of our research was to study the composition of Pseudo‐nitzschia species during a period when neurotoxin domoic acid (DA) was present in shellfish. Sampling was conducted in Kaštela Bay (Central Adriatic Sea), between November 2015 and January 2016. Concentrations of DA analyzed in various shellfish species were low, below the regulatory limit, while the highest abundance of Pseudo‐nitzschia spp. reached 1.85 × 105 cells L−1 in the surface layer, at the beginning of November. Within the temperature and salinity range recorded during the investigated period, a positive correlation of Pseudo‐nitzschia spp. abundance was recorded with temperature. Morphological analyses by scanning electron microscopy revealed the presence of five Pseudo‐nitzschia species that had already been reported in the Adriatic Sea – P. calliantha, P. delicatissima, P. fraudulenta, P. pseudodelicatissima /P. cuspidata and P. subfraudulenta – as well as an unknown Pseudo‐nitzschia sp. The composition of the Pseudo‐nitzschia assemblage changed over the investigated period. The species P. pseudodelicatissima/P.cuspidata was found throughout the entire period and the highest diversity was noticed in January, when all six observed species were recorded. These results represent the first taxonomical investigation of the genus Pseudo‐nitzschia in Kaštela Bay, as well as the first report of DA in shellfish from this area.

Understanding the blob bloom: Warming increases toxicity and abundance of the harmful bloom diatom Pseudo-nitzschia in California coastal waters

The toxic diatom genus Pseudo-nitzschia produces environmentally damaging harmful algal blooms (HABs) along the U.S. west coast and elsewhere, and a recent ocean warming event coincided with toxic blooms of record extent. This study examined the effects of temperature on growth, domoic acid toxin production, and competitive dominance of two Pseudo-nitzschia species from Southern California. Growth rates of cultured P. australis were maximal at 23°C (∼0.8d−1), similar to the maximum temperature recorded during the 2014–2015 warming anomaly, and decreased to ∼0.1 d−1 by 30°C. In contrast, cellular domoic acid concentrations only became detectable at 23°C, and increased to maximum levels at 30°C. In two incubation experiments using natural Southern California phytoplankton communities, warming also increased the relative abundance of another potentially toxic local species, P. delicatissima. These results suggest that both the toxicity and the competitive success of particular Pseudo-nitzschia spp. can be positively correlated with temperature, and therefore there is a need to determine whether harmful blooms of this diatom genus may be increasingly prevalent in a warmer future coastal ocean.

Causality of an extreme harmful algal bloom in Monterey Bay, California, during the 2014–2016 northeast Pacific warm anomaly

AbstractAn ecologically and economically disruptive harmful algal bloom (HAB) affected much of the northeast Pacific margin in 2015, during a prolonged oceanic warm anomaly. Caused by diatoms of the genus Pseudo‐nitzschia, this HAB produced the highest particulate concentrations of the biotoxin domoic acid (DA) ever recorded in Monterey Bay, California. Bloom inception followed strong upwelling during the spring transition, which introduced nutrients and eliminated the warm anomaly locally. Subsequently, moderate and intermittent upwelling created favorable conditions for growth and accumulation of HAB biomass, which was dominated by a highly toxigenic species, P. australis. High cellular DA concentrations were associated with available nitrogen for DA synthesis coincident with silicate exhaustion. This nutrient influence resulted from two factors: (1) disproportionate depletion of silicate in upwelling source waters during the warm anomaly, the most severe depletion observed in 24 years, and (2) silicate uptake by the dense diatom bloom.

Inter and intra-specific growth and domoic acid production in relation to nutrient ratios and concentrations in Pseudo-nitzschia: phosphate an important factor

The factors responsible for inducing the synthesis of toxins and responses from toxic phytoplankton blooms remain unclear. In this study we compare the influence of genotypic (at both the intra and interspecific levels) and environmental factors (nutrient concentration and ratio) on growth (in terms of cell densities) and domoic acid (DA) production in three Pseudo-nitzschia species: P. australis, P.pungens and P.fradulenta. A strong phosphate effect was detected. More precisely, a low initial concentration in phosphate, even at high initial nitrogen and silicate concentrations, induced the highest DA concentrations and the lowest cell densities in all strains/species studied. In contrast, a low initial concentration of nitrogen and silicate combined, with a higher phosphate concentration resulted in low cell densities, but without high DA production. Inter-species effects were also observed in DA production, where P. australis represented the most toxigenic species of all. Intra-specific variations were only moderate, except for a recently isolated P. australis strain, suggesting the influence of time since isolation on the physiology and DA production of Pseudo-nitzschia species. Overall, the lack of strong interaction between environmental and genotypic factors showed that the various genotypes investigated did not extensively diverge in their ability to respond (in terms of DA production and cell densities) to contrasting nutrient supply.