Effect of CO2 on growth and toxicity of Alexandrium tamarense from the East China Sea,a major producer of paralytic shellfish toxins

In recent decades, the frequency and intensity of harmful algal blooms (HABs), as well as a profusion of toxic phytoplankton species, have significantly increased in coastal regions of China. Researchers attribute this to environmental changes such as rising atmospheric CO₂ levels. Such addition of carbon into the ocean ecosystem can lead to increased growth, enhanced metabolism, and altered toxicity of toxic phytoplankton communities resulting in serious human health concerns. In this study, the effects of elevated partial pressure of CO₂ (pCO₂) on the growth and toxicity of a strain of Alexandrium tamarense (ATDH) widespread in the East and South China Seas were investigated. Results of these studies showed a higher specific growth rate (0.31 ± 0.05 day⁻¹) when exposed to 1000 μatm CO₂, (experimental), with a corresponding density of (2.02 ± 0.19) × 10⁷ cells L⁻¹, that was significantly larger than cells under 395 μatm CO₂₍control). These data also revealed that elevated pCO₂ primarily affected the photosynthetic properties of cells in the exponential growth phase. Interestingly, measurement of the total toxin content per cell was reduced by half under elevated CO₂ conditions. The following individual toxins were measured in this study: C1, C2, GTX1, GTX2, GTX3, GTX4, GTX5, STX, dcGTX2, dcGTX3, and dcSTX. Cells grown in 1000 μatm CO₂ showed an overall decrease in the cellular concentrations of C1, C2, GTX2, GTX3, GTX5, STX, dcGTX2, dcGTX3, and dcSTX, but an increase in GTX1 and GTX4. Total cellular toxicity per cell was measured revealing an increase of nearly 60% toxicity in the presence of elevated CO₂ compared to controls. This unusual result was attributed to a significant increase in the cellular concentrations of the more toxic derivatives, GTX1 and GTX4.Taken together; these findings indicate that the A. tamarense strain ATDH isolated from the East China Sea significantly increased in growth and cellular toxicity under elevated pCO₂ levels. These data may provide vital information regarding future HABs and the corresponding harmful effects as a result of increasing atmospheric CO₂.     

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 (∼0.8 d⁻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.     

Elevated seawater levels of CO2 change the metabolic fingerprint of tissues and hemolymph from the green shore crab Carcinus maenas

Carbon dioxide (CO₂) acts as a weak acid in water and the increasing level of CO₂ in the atmosphere leads to ocean acidification. In addition, possible leakage from sub-seabed storage of anthropogenic CO₂ may pose a threat to the marine environment. ¹H NMR spectroscopy was applied to extracts of hemolymph, gills and leg muscle from shore crabs (Carcinus maenas) to examine the metabolic response to elevated levels of CO₂. Crabs were exposed to different levels of CO₂‐acidified seawater with pH_NBS 7.4, 6.6 and 6.3 (pCO₂ ~ 2600, 16,000 and 30,000 μatm, respectively) for two weeks (level-dependent exposure). In addition, the metabolic response was followed for up to 4 weeks of exposure to seawater pH_NBS 6.9 (pCO₂ ~ 7600 μatm). Partial least squares regression analysis of data showed an increased differentiation between metabolic fingerprints of controls and exposed groups for all sample types with increasing CO₂ levels. Difference between controls and animals subjected to time-dependent exposure appeared after 4 weeks in the hemolymph and gills, and after 48 h of exposure in the leg muscle. Changes in metabolic profiles were mainly due to a reduced level of important intracellular osmolytes such as amino acids (glycine, proline), while the level of other metabolites varied between the different sample types. The results are similar to what is observed in animals exposed to hypo-osmotic stress and may suggest disturbances in intracellular iso-osmotic regulation. The results may also reflect increased catabolism of amino acids to supply the body fluids with proton-buffering ammonia (NH₃). Alternatively, the findings may reflect an exhaustive effect of CO₂ exposure.     

The Response of Antarctic Sea Ice Algae to Changes in pH and CO2

Ocean acidification substantially alters ocean carbon chemistry and hence pH but the effects on sea ice formation and the CO₂ concentration in the enclosed brine channels are unknown. Microbial communities inhabiting sea ice ecosystems currently contribute 10–50% of the annual primary production of polar seas, supporting overwintering zooplankton species, especially Antarctic krill, and seeding spring phytoplankton blooms. Ocean acidification is occurring in all surface waters but the strongest effects will be experienced in polar ecosystems with significant effects on all trophic levels. Brine algae collected from McMurdo Sound (Antarctica) sea ice was incubated in situ under various carbonate chemistry conditions. The carbon chemistry was manipulated with acid, bicarbonate and bases to produce a pCO₂ and pH range from 238 to 6066 µatm and 7.19 to 8.66, respectively. Elevated pCO₂ positively affected the growth rate of the brine algal community, dominated by the unique ice dinoflagellate, Polarella glacialis. Growth rates were significantly reduced when pH dropped below 7.6. However, when the pH was held constant and the pCO₂ increased, growth rates of the brine algae increased by more than 20% and showed no decline at pCO₂ values more than five times current ambient levels. We suggest that projected increases in seawater pCO₂, associated with OA, will not adversely impact brine algal communities.     

The dinoflagellate Akashiwo sanguinea will benefit from future climate change: The interactive effects of ocean acidification,warming and high irradiance on photophysiology and hemolytic activity

Due to global climate change, marine phytoplankton will likely experience low pH (ocean acidification), high temperatures and high irradiance in the future. Here, this work report the results of a batch culture experiment conducted to study the interactive effects of elevated CO₂, increased temperature and high irradiance on the harmful dinoflagellate Akashiwo sanguinea, isolated at Dongtou Island, Eastern China Sea. The A. sanguinea cells were acclimated in high CO₂ condition for about three months before testing the responses of cells to a full factorial matrix experimentation during a 7-day period. This study measured the variation in physiological parameters and hemolytic activity in 8 treatments, representing full factorial combinations of 2 levels each of exposure to CO₂ (400 and 1000 μatm), temperature (20 and 28 °C) and irradiance (50 and 200 μmol photons m⁻² s⁻¹). Sustained growth of A. sanguinea occurred in all treatments, but high CO₂ (HC) stimulated faster growth than low CO₂ (LC). The pigments (chlorophyll a and carotenoid) decreased in all HC treatments. The quantum yield (F_v/F_m) declined slightly in all high-temperature (HT) treatments. High irradiance (HL) induced the accumulation of ultraviolet-absorbing compounds (UV_abc) irrespective of temperature and CO₂. The hemolytic activity in the LC treatments, however, declined when exposed to HT and HL, but HC alleviated the adverse effects of HT and HL on hemolytic activity. All HC and HL conditions and the combinations of high temperature*high light (HTHL) and high CO₂*high temperature*high light (HCHTHL) positively affected the growth in comparison to the low CO₂*low temperature*low light (LCLTLL) treatment. High temperature (HT), high light (HL) and a combination of HT*HL, however, negatively impacted hemolytic activity. CO₂ was the main factor that affected the growth and hemolytic activity. There were no significant interactive effects of CO₂*temperature*irradiance on growth, pigment, F_v/F_m or hemolytic activity, but there were effects on P_m, α, and E_k. If these results are extrapolated to the natural environment, it can be hypothesized that A. sanguinea cells will benefit from the combination of ocean acidification, warming, and high irradiance that are likely to occur under future climate change. It is assumed that faster growth and higher hemolytic activity and UV_abc of this species will occur under future conditions compared with those the current CO₂ (400 μatm) and temperature (20 °C) conditions.     

Signals of resilience to ocean change: high thermal tolerance of early stage Antarctic sea urchins (Sterechinus neumayeri) reared under present-day and future pCO2 and temperature

We tested the hypothesis that development of the Antarctic urchin Sterechinus neumayeri under future ocean conditions of warming and acidification would incur physiological costs, reducing the tolerance of a secondary stressor. The aim of this study is twofold: (1) quantify current austral spring temperature and pH near sea urchin habitat at Cape Evans in McMurdo Sound, Antarctica and (2) spawn S. neumayeri in the laboratory and raise early developmental stages (EDSs) under ambient (?0.7 °C; 400 µatm pCO₂) and future (+2.6 °C; 650 and 1,000 µatm pCO₂) ocean conditions and expose four EDSs (blastula, gastrula, prism, and 4-arm echinopluteus) to a one hour acute heat stress and assess survivorship. Results of field data from 2011 to 2012 show extremely stable inter-annual pH conditions ranging from 7.99 to 8.08, suggesting that future ocean acidification will drastically alter the pH-seascape for S. neumayeri. In the laboratory, S. neumayeri EDSs appear to be tolerant of temperatures and pCO₂ levels above their current habitat conditions. EDSs survived acute heat exposures >20 °C above habitat temperatures of ?1.9 °C. No pCO₂ effect was observed for EDSs reared at ?0.7 °C. When reared at +2.6 °C, small but significant pCO₂ effects were observed at the blastula and prism stage, suggesting that multiple stressors are more detrimental than single stressors. While surprisingly tolerant overall, blastulae were the most sensitive stage to ocean warming and acidification. We conclude that S. neumayeri may be unexpectedly physiologically tolerant of future ocean conditions.     

Detrimental impacts of the dinoflagellate Karenia mikimotoi in Fujian coastal waters on typical marine organisms

Blooms of the toxic dinoflagellate Karenia mikimotoi (K. mikimotoi) have occurred frequently in the East China Sea in recent decades and were responsible for massive mortalities of abalones in Fujian coastal areas in 2012, however, little is known about the effects of these blooms on other marine organisms. In this study, the toxic effects and the possible mechanisms of toxicity of K. mikimotoi from Fujian coastal waters on typical marine organisms at different trophic levels, including zooplankton (Brachionus plicatilis, Artemia salina, Calanus sinicus, and Neomysis awatschensis) and aquaculture species (Penaeus vannamei and Scophthalmus maximus) were investigated. At a bloom density of 3 × 10⁴ cells/mL, the Fujian strain of K. mikimotoi significantly affected the tested organisms, which had mortality rates at 96 h of 100, 23, 20, 97, 33, and 53%, respectively. Moreover, the intact cell suspension was toxic to all tested species, whereas cell-free culture and the ruptured cell suspension had no significant effects on the tested organisms. Possible mechanisms for this toxic effect, including reactive oxygen species (ROS) and hemolytic toxins, were evaluated. For K. mikimotoi, 0.014 ± 0.004 OD/(10⁴ cells) superoxide (O₂⁻) and 3.00 ± 0.00 nmol/(10⁴ cells) hydrogen peroxide (H₂O₂) were measured, but hydrogen peroxide did not affect rotifers at that concentration, and rotifers were not protected from the lethal effects of K. mikimotoi when the enzymes superoxide dismutase and catalase were added to counteract the ROS. The lipophilic extract of K. mikimotoi had a hemolytic effect on rabbit erythrocytes but exhibited no significant toxicity. These results suggest that this strain of K. mikimotoi can have detrimental effects on several typical marine organisms and that its toxicity may be associated with intact cells but is not related to ROS or hemolytic toxins.     

Comparative study on the PSP component and toxicity produced by Alexandrium tamiyavanichii (Dinophyceae) strains occurring in Japanese coastal water

In December 2001, a large-scale bloom of the paralytic shellfish toxin-producing dinoflagellate, Alexandrium tamiyavanichii Balech (Dinophyceae) was observed in the Seto Inland Sea, Japan. During the bloom, we conducted a field survey in the Seto Inland Sea and collected samples of bloom water in order to assess the toxicity and toxic components of A. tamiyavanichii. The results of the field survey indicated that A. tamiyavanichii was observed frequently at water temperatures between 17.8 and 20.0 °C, and the maximum cell density at the four localities was ca. 2000 cells L^?1 (Fukuyama Bay). To elucidate the toxicity and toxic components of A. tamiyavanichii, 54 strains (28 strains from Fukuyama Bay, 12 strains from Kasato Bay, 9 strains from Uchinoumi, and 5 strains from Inokushi Bay) were established from bloom water samples, and were then subject of toxin analyses via fluorescence HPLC. The toxic components of A. tamiyavanichii showed that N-sulfocarbamoyl (C-) 2 and Gonyautoxins (GTX) 4 were the principal toxins and C3+4, GTX 2+3, GTX 5, neosaxitoxin (neoSTX) and saxitoxin (STX) were minor components. The toxicity of the A. tamiyavanichii cells was higher than that of the other toxic species, A. tamarense and A. catenella. The toxic components in all strains among the four localities were closely related, and thus the recent A. tamiyavanichii population in the Seto Inland Sea appears to originate from a single population.     

Toxin production,retention, and extracellular release by Dinophysis acuminata during extended stationary phase and culture decline

Dinophysis spp. produce diarrhetic shellfish poisoning (DSP) toxins and pectenotoxins. The extent to which the dinoflagellate cells retain their toxicity in stationary phase, a period when cells are most toxic, and their transition into cell death is not known. Here we present results on the production, recycling, retention, and release of toxins from a monoculture of Dinophysis acuminata during these two important stages. Once stationary phase was reached, cultures were divided between light and dark treatments to identify if light influenced toxin dynamics. Light was required for long-term cell maintenance (>2 months) of D. acuminata in the absence of prey, however, in the dark, cells in stationary phase survived on reserves alone for four weeks before beginning to decline. Cells maintained relatively constant levels of intracellular OA (0.39 ± 0.03 pg/cell, 0.44 ± 0.05 pg/cell), DTX1 (0.45 ± 0.09 pg/cell, 0.64 ± 0.10 pg/cell) and PTX2 (10.4 ± 1.4 pg/cell, 11.0 ± 1.9 pg/cell) in the dark and light treatments, respectively, throughout stationary phase and into culture decline. Toxin production was only apparent during late exponential and early stationary growth when cells were actively dividing. In general, the concentration of dissolved (extracellular) toxin in the medium significantly increased upon culture aging and decline; cells did not appear to be actively or passively releasing toxin during stationary phase, but rather extracellular release was likely a result of cell death. Light availability did not have an apparent effect on toxin production, quotas, or intracellular vs. extracellular distribution. Together these results suggest that a bloom of D. acuminata would retain its cellular toxicity or potency as long as the population is viable, and that cells under conditions of low light (e.g., at the boundary or below euphotic zone) and/or minimal prey could maintain toxicity for extended periods.     

The capability of several toxic plants to condition taste aversions in sheep

Grazing livestock frequently ingest toxic plants, occasionally with fatal results. Behavioral adjustments by livestock may reduce toxin intake; for example they can develop food aversions which may protect animals from over-ingestion of toxic plants. The purpose of this study was to evaluate three plants with different mechanisms of toxicity for their efficacy in conditioning a taste aversion: (1) a seleniferous plant, Xylorhiza glabriuscula, (2) an indolizidine alkaloid-containing plant, Astragalus lentiginosus, and (3) a diterpene acid-containing plant, Gutierrezia sarothrae. For each plant species, 15 sheep were divided into 3 treatment groups and periodically tested for consumption of a novel food, whole corn: (1) controls – given 200 g of ground alfalfa hay by oral gavage, (2) averted – given lithium chloride (LiCl) at 175 mg/kg BW via oral gavage, and (3) given the specific target plant by oral gavage. X. glabriuscula was given at a dose equivalent to 3 mg Se/kg BW; A. lentiginosus was given at a dose equivalent to 3 mg/kg of the toxic alkaloid, swainsonine; freshly thawed G. sarothrae was dosed at 5 g/kg body weight (BW). Both LiCl and Xylorhiza conditioned an aversion to corn, with sheep eating 1.6 and 0.6% of offered corn during the final test; controls were not averted, eating 93% of the corn (P < 0.01). Sheep were partially averted by Xylorhiza after a single dose, and the aversion was complete after the second dose. Sheep were not averted by A. lentiginosus or G. sarothrae. Of the three toxic plants used in this study, only Xylorhiza conditioned a taste aversion. These results likely reflect differing mechanisms of action of the plant toxin(s) on brain and gut structures important for forming conditioned taste aversions. These results suggest that conditioned aversions to Se-containing plants may help to deter consumption of such plants by grazing ruminants on rangelands.     

End of the Century pCO2 Levels Do Not Impact Calcification in Mediterranean Cold-Water Corals

Ocean acidification caused by anthropogenic uptake of CO₂ is perceived to be a major threat to calcifying organisms. Cold-water corals were thought to be strongly affected by a decrease in ocean pH due to their abundance in deep and cold waters which, in contrast to tropical coral reef waters, will soon become corrosive to calcium carbonate. Calcification rates of two Mediterranean cold-water coral species, Lophelia pertusa and Madrepora oculata, were measured under variable partial pressure of CO₂ (pCO₂) that ranged between 380 µatm for present-day conditions and 930 µatm for the end of the century. The present study addressed both short- and long-term responses by repeatedly determining calcification rates on the same specimens over a period of 9 months. Besides studying the direct, short-term response to elevated pCO₂ levels, the study aimed to elucidate the potential for acclimation of calcification of cold-water corals to ocean acidification. Net calcification of both species was unaffected by the levels of pCO₂ investigated and revealed no short-term shock and, therefore, no long-term acclimation in calcification to changes in the carbonate chemistry. There was an effect of time during repeated experiments with increasing net calcification rates for both species, however, as this pattern was found in all treatments, there is no indication that acclimation of calcification to ocean acidification occurred. The use of controls (initial and ambient net calcification rates) indicated that this increase was not caused by acclimation in calcification response to higher pCO₂. An extrapolation of these data suggests that calcification of these two cold-water corals will not be affected by the pCO₂ level projected at the end of the century.     

Effect of 5-fluoro-2′-deoxyuridine on toxin production and cell cycle regulation in marine dinoflagellate,Alexandrium tamarense

The effect of metabolic inhibitor, 5-fluoro-2′-deoxyuridine (FUdR) on toxin production and the cell cycle of marine dinoflagellate, Alexandrium tamarense, was investigated. Compared to untreated cells, FUdR at 3 μM (p < 0.05) to 300 μM (p < 0.01) inhibited the cell proliferation and toxin production in a dose-dependent manner for A. tamarense cultured in modified T₁ medium. FUdR at 203 μM resulted in cell cycle arrest at the S phase at day 4 and toxigenesis was inhibited after day 2. The toxin profiles of the FUdR-treated cultures were similar to those of the control culture. These results suggest that FUdR inhibits saxitoxin (STX) biosynthesis in the early stage of the pathway. This report is the first to demonstrate the inhibition of toxin production in A. tamarense by a nucleoside analog.     

Marine snow formation by the toxin-producing diatom,Pseudo-nitzschia australis

The formation of marine snow (MS) by the toxic diatom Pseudo-nitschia australis was simulated using a roller table experiment. Concentrations of particulate and dissolved domoic acid (pDA and dDA) differed significantly among exponential phase and MS formation under simulated near surface conditions (16 °C/12:12-dark:light cycle) and also differed compared to subsequent particle decomposition at 4 °C in the dark, mimicking conditions in deeper waters. Particulate DA was first detected at the onset of exponential growth, reached maximum levels associated with MS aggregates (1.21 ± 0.24 ng mL⁻¹) and declined at an average loss rate of ∼1.2% pDA day⁻¹ during particle decomposition. Dissolved DA concentrations increased throughout the experiment and reached a maximum of ∼20 ng mL⁻¹ at final sampling on day 88. The succession by P. australis from active growth to aggregation resulted in increasing MS toxicity and based on DA loading of particles and known in situ sinking speeds, a significant amount of toxin could have easily reached the deeper ocean or seafloor. MS formation was further associated with significant dDA accumulation at a ratio of pDA: dDA: cumulative dDA of approximately 1:10:100. Overall, this study confirms that MS functions as a major vector for toxin flux to depth, that Pseudo-nitzschia-derived aggregates should be considered ‘toxic snow’ for MS-associated organisms, and that effects of MS toxicity on interactions with aggregate-associated microbes and zooplankton consumers warrant further consideration.     

The combined effect of salinity and temperature on the growth and toxin content of four Chilean strains of Alexandrium catenella (Whedon and Kofoid) Balech 1985 (Dinophyceae) isolated from an outbreak occurring in southern Chile in 2009

The toxic dinoflagellate Alexandrium catenella has been detected in the southern Chile since 1972, causing severe negative impacts on public health and aquaculture activities. Several environmental factors have been determined to affect growth and toxin production in Alexandrium strains. The aim of this study was to determine the effect of four combined conditions of two temperatures (10 and 15 °C) and two salinities (15 and 35 psu) on the growth and the Paralytic Shellfish Poisoning (PSP) toxin content and composition in four Chilean strains of A. catenella (PFB41, PFB42, PFB37 and PFB38), isolated during a summer outbreak occurred in southern Chile in 2009. The growth curves showed a higher effect of the salinity in strains PFB41 and PFB42 than in strains PFB37 and PFB38. The values of growth rates and maximum cell densities ranged from 0.25 to 0.73 div day⁻¹ and 1.1 × 10⁴ to 5.2 × 10⁴ cells mL⁻¹, respectively. All of the strains showed the highest values for both growth parameters at 15 °C and 35 psu. In general, growth parameters were higher at 35 psu independently of the temperature. On the other hand, the total PSP toxin content ranged widely from 3.99 to 239 fmol cell⁻¹. The highest values of PSP toxin content were attained at 10 °C and 35 psu for all of the strains, at both stages of growth. All of the strains displayed different toxin compositions, with neoSTX, GTX4-1, GTX3-2 and GTX5 being the main toxins detected. The results showed significant differences in the absolute values of growth and toxin production parameters among the strains grown under the same culture conditions, and for each strain grown under different combined conditions of temperature and salinity. These findings demonstrate that abiotic factors can differentially affect the population dynamics of the A. catenella toxic genotypes, thus making it extremely difficult to predict the ecological behavior of this species in the field in terms of the intensity of a potential outbreak.     

Estimating the contribution of N-sulfocarbamoyl paralytic shellfish toxin analogs GTX6 and C3 + 4 to the toxicity of mussels (Mytilus galloprovincialis) over a bloom of Gymnodinium catenatum

Gymnodinium catenatum, a dinoflagellate species with a global distribution, is known to produce paralytic shellfish poisoning (PSP) toxins. The profile of toxins of G. catenatum is commonly dominated by sulfocarbamoyl analogs including the C3 + 4 and GTX6, which to date has no commercial certified reference materials necessary for their quantification via chemical methods, such as liquid chromatography. The aim of this study was to assess the presence of C3 + 4 and GTX6 and their contribution to shellfish toxicity. C3 + 4 and GTX6 were indirectly quantified via pre-column oxidation liquid chromatography with fluorescence detection after hydrolysis conversion into their carbamate analogs. Analyses were carried out in mussel samples collected over a bloom of G. catenatum (>63 × 10³ cells l⁻¹) in Aveiro lagoon, NW Portuguese coast. Concentration levels of sulfocarbamoyl toxin analogs were two orders of magnitude higher than decarbamoyl toxins, which were in turn one order of magnitude higher than carbamoyl toxins. Among the sulfocarbamoyl toxins, C1 + 2 were clearly the dominant compounds, followed by C3 + 4 and GTX6. The least abundant sulfocarbamoyl toxin was GTX5. The most important compounds in terms of contribution for sample toxicity were C1 + 2, which justified 26% of the PSP toxicity. The lesser abundant dcSTX constitutes the second most important compound with similar % of toxicity to C1 + 2, C3 + 4 and GTX6 were responsible for approximately 11% and 13%, respectively. The median of the sum of C3 + 4 and GTX6 was 27%. These levels reached a maximum of 60% as was determined for the sample collected closest to the G. catenatum bloom. This study highlights the importance of these low potency PSP toxin analogs to shellfish toxicity. Hydrolysis conversion of C3 + 4 and GTX6 is recommended for determination of PSP toxicity when LC detection methods are used for PSP testing in samples exposed to G. catenatum.     

Evidence of freshwater algal toxins in marine shellfish: Implications for human and aquatic health

The occurrence of freshwater harmful algal bloom toxins impacting the coastal ocean is an emerging threat, and the potential for invertebrate prey items to concentrate toxin and cause harm to human and wildlife consumers is not yet fully recognized. We examined toxin uptake and release in marine mussels for both particulate and dissolved phases of the hepatotoxin microcystin, produced by the freshwater cyanobacterial genus Microcystis. We also extended our experimental investigation of particulate toxin to include oysters (Crassostrea sp.) grown commercially for aquaculture. California mussels (Mytilus californianus) and oysters were exposed to Microcystis and microcystin toxin for 24 h at varying concentrations, and then were placed in constantly flowing seawater and sampled through time simulating riverine flushing events to the coastal ocean. Mussels exposed to particulate microcystin purged the toxin slowly, with toxin detectable for at least 8 weeks post-exposure and maximum toxin of 39.11 ng/g after exposure to 26.65 μg/L microcystins. Dissolved toxin was also taken up by California mussels, with maximum concentrations of 20.74 ng/g after exposure to 7.74 μg/L microcystin, but was purged more rapidly. Oysters also took up particulate toxin but purged it more quickly than mussels. Additionally, naturally occurring marine mussels collected from San Francisco Bay tested positive for high levels of microcystin toxin. These results suggest that ephemeral discharge of Microcystis or microcystin to estuaries and the coastal ocean accumulate in higher trophic levels for weeks to months following exposure.     

Phylomineralogy of the Coralline red algae: Correlation of skeletal mineralogy with molecular phylogeny

The coralline algae in the orders Corallinales and Sporolithales (subclass Corallinophycidae), with their high degree of mineralogical variability, pose a challenge to projections regarding mineralogy and response to ocean acidification. Here we relate skeletal carbonate mineralogy to a well-established phylogenetic framework and draw inferences about the effects of future changes in sea-water chemistry on these calcified red algae. A collection of 191 coralline algal specimens from New Zealand, representing 13 genera and 28 species, included members of three families: Corallinaceae, Hapalidiaceae, and Sporolithaceae. While most skeletal specimens were entirely calcitic (range: 73–100 wt.% calcite, mean 97 wt.% calcite, std dev = 5, n = 172), a considerable number contained at least some aragonite. Mg in calcite ranged from 10.5 to 16.4 wt.% MgCO₃, with a mean of 13.1 wt.% MgCO₃ (std dev = 1.1, n = 172). The genera Mesophyllum and Lithophyllum were especially variable. Growth habit, too, was related to mineralogy: geniculate coralline algae do not generally contain any aragonite. Mg content varied among coralline families: the Corallinaceae had the highest Mg content, followed by the Sporolithaceae and the Hapalidiaceae. Despite the significant differences among families, variation and overlap prevent the use of carbonate mineralogy as a taxonomic character in the coralline algae. Latitude (as a proxy for water temperature) had only a slight relationship to Mg content in coralline algae, contrary to trends observed in other biomineralising taxa. Temperate magnesium calcites, like those produced by coralline algae, are particularly vulnerable to ocean acidification. Changes in biomineralisation or species distribution may occur over the next few decades, particularly to species producing high-Mg calcite, as pH and CO₂ dynamics change in coastal temperate oceans.     

Toxic and non-toxic strains of Microcystis aeruginosa induce temperature dependent allelopathy toward growth and photosynthesis of Chlorella vulgaris

Global warming was believed to accelerate the expansion of cyanobacterial blooms. However, the impact of changes due to the allelopathic effects of cyanobacterial blooms with or without algal toxin production on the ecophysiology of its coexisting phytoplankton species arising from global warming were unknown until recently. In this study, the allelopathic effects of toxic and non-toxic Microcystis aeruginosa strains on the growth of green alga Chlorella vulgaris and photosynthesis of the co-cultivations of C. vulgaris and toxic M. aeruginosa FACHB-905 or non-toxic M. aeruginosa FACHB-469 were investigated at different temperatures. The growth of C. vulgaris, co-cultured with the toxic or non-toxic M. aeruginosa strains, was promoted at 20 °C but inhibited at temperatures ≥25 °C. The inhibitory effects of the toxic and non-toxic M. aeruginosa strains on of the co-cultivations (C. vulgaris and non-toxic M. aeruginosa FACHB-469 or toxic M. aeruginosa FACHB-905) also linearly increased with elevated temperatures. Furthermore, toxic M. aeruginosa FACHB-905 induced more inhibition toward growth of C. vulgaris or P_max and R_d of the mixtures than non-toxic M. aeruginosa FACHB-469. C. vulgaris dominated over non-toxic M. aeruginosa FACHB-469 but toxic M. aeruginosa FACHB-905 overcame C. vulgaris when they were co-cultured in mesocosms in water temperatures from 20 to 25 °C. The results indicate that allelopathic effects of M. aeruginosa strains on C. vulgaris are both temperature- and species-dependent: it was stimulative for C. vulgaris at low temperatures such as 20 °C, but inhibitory at high temperatures (≥25 °C); the toxic strain was determined to be more harmful to C. vulgaris than the non-toxic one. This suggests that global warming may aggravate the ecological risk of cyanobacteria blooms, especially those with toxic species as the main contributors.     

Molecular ecological responses of the dinoflagellate Karenia mikimotoi to phosphate stress

Karenia mikimotoi is a toxic, widespread dinoflagellate which could produce hemolytic toxins and ichthyotoxins affecting fisheries within the area of its bloom. Previous ecophysiological studies indicated that the enhance of environmental phosphate concentration could promote the growth of K. mikimotoi. Intrinsic mechanisms regarding the effects of external phosphate on its photosynthesis, cell cycle succession and differential proteins’ expressions are still unknown. K. mikimotoi was cultured in phosphate-deprived medium, while the culture in f/2 medium (Guillard, 1975) was introduced as phosphate-sufficient control experiment. Cell counts and phosphate concentration detection were performed every other day. Flowcytometry was applied to measure cell cycle succession and chlorophyll fluorescence intensity fluctuation. Differential proteomics expression was examined by SDS-PAGE tandem LTQ Orbitrap MS/MS spectrometry. Functions of each differential protein were searched within NCBInr protein database and Swissprot database. Our study demonstrated that phosphate stress inhibited growth and cell cycle succession of K. mikimotoi remarkably (p < 0.01). Algal chlorophyll fluorescence intensity was significantly affected by phosphate deprivation (p < 0.05). 11 species of differential proteins were detected only in phosphate-limited culture sample which related to stress signal transduction, vacuolar phosphate release, phospholipid degradation, organic acid synthesis and phagotrophy. 4 kinds of differential proteins were identified only in f/2 medium culture sample which referred to cell proliferation, glycolysis, SAM cycle and polyamine production. Based on analysis of differential proteomic functional annotation, we hypothesized proteomic response mechanism of K. mikimotoi to phosphate stress. Molecular biological responses of dinoflagellate K. mikimotoi to phosphate stress was explored.