Harmful Algal Bloom Species Research Articles

Use of biological trait analysis of periphytic protozoan assemblages for evaluating effects of harmful algal blooms on ecological quality status in marine ecosystem

The effects of two harmful algal bloom (HAB) species Alexandrium tamarense and Gymnodinium catenatum on ecological quality status were studied using 14-day protozoan samples as test organisms. A fuzzy coding system with four traits and 11 categories of the test organisms was used for biological trait analysis. Five treatments were designed following the concentrations of 100, 102, 103, 104 and 105 cell ml‐1 of each algal species. The community-weighted means were used to summarize the functioning process of the test organism assemblages. The community functioning of the protozoa showed a significant change in the treatments with high algal concentrations (104 and 105 cell ml−1). The functional richness of the test organisms showed continuous increasing trend from 102 to 104 cell ml−1, and sharply dropped. These findings suggest that the BTA may be used as a useful tool for assessing the effects of HABs on ecological quality status in marine ecosystems.

Recent Progress in the Study of Peroxiredoxin in the Harmful Algal Bloom Species Chattonella marina.

Peroxiredoxin (Prx) is a relatively recently discovered antioxidant enzyme family that scavenges peroxides and is known to be present in organisms from biological taxa ranging from bacteria to multicellular eukaryotes, including photosynthetic organisms. Although there have been many studies of the Prx family in higher plants, green algae, and cyanobacteria, few studies have concerned raphidophytes and dinoflagellates, which are among the eukaryotic algae that cause harmful algal blooms (HABs). In our proteomic study using 2-D electrophoresis, we found a highly expressed 2-Cys peroxiredoxin (2-CysPrx) in the raphidophyte Chattonella marina var. antiqua, a species that induces mass mortality of aquacultured fish. The abundance of the C. marina 2-CysPrx enzyme was highest in the exponential growth phase, during which photosynthetic activity was high, and it then decreased by about a factor of two during the late stationary growth phase. This pattern suggested that 2-CysPrx is a key enzyme involved in the maintenance of high photosynthesis activity. In addition, the fact that the depression of photosynthesis by excessively high irradiance was more severe in the 2-CysPrx low-expression strain (wild type) than in the normal-expression strain (wild type) of C. marina suggested that 2-CysPrx played a critical role in protecting the cell from oxidative stress caused by exposure to excessively high irradiance. In the field of HAB research, estimates of growth potential have been desired to predict the population dynamics of HABs for mitigating damage to fisheries. Therefore, omics approaches have recently begun to be applied to elucidate the physiology of the growth of HAB species. In this review, we describe the progress we have made using a molecular physiological approach to identify the roles of 2-CysPrx and other antioxidant enzymes in mitigating environmental stress associated with strong light and high temperatures and resultant oxidative stress. We also describe results of a survey of expressed Prx genes and their growth-phase-dependent behavior in C. marina using RNA-seq analysis. Finally, we speculate about the function of these genes and the ecological significance of 2-CysPrx, such as its involvement in circadian rhythms and the toxicity of C. marina to fish.

Mitochondrial genome of the harmful algal bloom species Odontella regia (Mediophyceae, Bacillariophyta)

Recent development of DNA sequencing technologies has enabled successful construction of thousands of mitochondrial genomes. Nevertheless, only 33 mitochondrial genomes have been reported for species in Bacillariophyta, which includes harmful algal bloom (HAB) species. In this study, we determined the complete mitogenome of the Bacillariophyta HAB species Odontella regia. For comparison, we also constructed the mitogenome of Lithodesmium undulatum, another Bacillariophyta species. Both strains were isolated in the Jiaozhou Bay, an epitome of China’s coastal ecosystem and an ideal site for HAB research. These two mitogenomes were characterized as 37,617 bp and 37,057 bp circular-mapping molecules with AT content of 73.4% and 75.3%, respectively. The phylogenetic tree based on 32 protein-coding genes of the mitogenome encoded in 35 Bacillariophyta species revealed that the class Mediophyceae consisted of multi-phyletic clades. While O. regia formed an independent clade, L. undulatum was closely related to Thalassiosira pseudonana and Skeletonema marinoi. Synteny comparison of O. regia and L. undulatum mitogenomes and mitogenomes of three closely related species displayed substantial differences among lineages in Mediophyceae by a series of gene translocations and/or inversion with many conserved gene blocks such as rpl2-rps19-rps3-rpl16-atp9. These analyses suggested a complex evolutionary relationship in Mediophyceae in which the mitogenome of O. regia was the least conservative compared with the mitogenomes of four other Bacillariophyta species. Further studies are needed to clarify detailed phylogenetic relationships in Bacillariophyta.

Oyster hatchery breakthrough of two HABs and potential effects on larval eastern oysters (Crassostrea virginica)

Harmful algal bloom (HAB) dinoflagellate species Karlodinium veneficum and Prorocentrum cordatum (prev. P. minimum) are commonly found in Chesapeake Bay during the late spring and early summer months, coinciding with the spawning season of the eastern oyster (Crassostrea virginica). Unexplained larval oyster mortalities at regional commercial hatcheries prompted screening of oyster hatchery water samples for these HAB species. Both HAB species were found in treated hatchery water during the oyster spawning season, sometimes exceeding bloom cell concentrations (≥ 1,000 cells/mL). To investigate the potential for these HAB species, independently or in co-exposure, to affect larval oyster mortality and activity, 96-h laboratory single and dual HAB bioassays with seven-day-old oyster larvae were performed. Treatments for the single HAB bioassay included fed and unfed controls, K. veneficum at 1,000; 5,000; 10,000; and 50,000 cells/mL, P. cordatum at 100; 5,000; 10,000; and 50,000 cells/mL. Subsequently, the 1,000 cells/mL K. veneficum and 50,000 cells/mL P. cordatum treatments were combined in a co-exposure treatment for the dual HAB bioassay. At all cell concentrations tested, K. veneficum swarmed oyster larvae and caused significant larval oyster mortality by 96 h (Karlo1,000: 21 ± 5%; Karlo5,000: 93 ± 2%; Karlo10,000: 85 ± 3%; Karlo50,000: 83 ± 5%, SE). In contrast, there was no significant difference in larval oyster mortality between the control treatments and any of the P. cordatum treatments by 96 h. By 24 h, larval oysters were significantly less active (immotile) in the presence of either HAB species as compared to control treatments (e.g., Karlo1,000: 37.8 ± 4.1%; Proro100: 47.3 ± 7.4%; Fed: 10.8 ± 3.2%; Unfed: 10.1 ± 4.9%, SE). In the dual HAB bioassay, larval oyster mortality associated with 1,000 cells/mL K. veneficum (44 ± 9%, SE) was not changed by the addition of 50,000 cells/mL P. cordatum (55 ± 7%, SE), demonstrating that K. veneficum was primarily responsible for the observed mortality. This study demonstrated that even low cell concentrations of K. veneficum and P. cordatum are harmful to larval oysters, and could contribute to reductions in oyster hatchery production through impacts on this critical life stage.

Red Sea MODIS Estimates of Chlorophyll a and Phytoplankton Biomass Risks to Saudi Arabian Coastal Desalination Plants

Harmful algal blooms (HABs) and the high biomass associated with them have afflicted marine desalination plants along coastal regions around the world. Few studies of HABs have been conducted in the Red Sea, where desalination plants along the Saudi Arabian Red Sea coast provide drinking water for millions of people. This study was conducted along the Saudi Arabian Red Sea coast from 2014 to 2015 to assess the potential for using Moderate Resolution Imaging Spectroradiometer (MODIS) remote sensing of chlorophyll a (Chl a) or fluorescence line height (FLH) to identify risks for biofouling at these desalination plants. Ship-based surveys of phytoplankton were conducted along the Saudi Arabian coastline offshore of desalination plants at Jeddah, Al Shoaibah and Al Qunfudhuh to assess the density of phytoplankton populations and identify any potential HAB species. Ship-based surveys showed low to moderate concentrations of phytoplankton, averaging from 1800–10,000 cells L−1 at Jeddah, 2000–11,000 cells L−1 at Al Shoaibah and 1000–20,500 cells L−1 at Al Qunfudhuh. Sixteen different species of potentially toxigenic HABs were identified through these surveys. There was a good relationship between ship-based total phytoplankton counts and monthly averaged coastal MODIS Chl a (R2 = 0.49, root mean square error (RMSE) = 0.27 mg m−3) or FLH (R2 = 0.47, RMSE = 0.04 mW m−2 µm−1 sr−1) values. Monthly average near shore Chl a concentrations obtained using MODIS satellite imagery were much higher in the Red Sea coastal areas at Al Qunfudhuh (maximum of about 1.3 mg m−3) than at Jeddah or Al Shoaibah (maximum of about 0.4 and 0.5 mg m−3, respectively). Chlorophyll a concentrations were generally highest from the months of December to March, producing higher risks of biofouling desalination plants than in other months. Concentrations decreased significantly, on average, from April to September. Long-term (2005–2016) monthly averaged MODIS Chl a values were used to delineate four statistically distinct zones of differing HAB biomass across the entire Red Sea. Sinusoidal functions representing monthly variability were fit to satellite Chl a values in each zone (RMSE values from 0.691 to 0.07 mg m−3, from Zone 1 to 4). December to January mean values and annual amplitudes for Chl a in these four sinusoidal functions decreased from Zones 1–4. In general, the greatest risk of HABs to desalination occurs during winter months in Zone 1 (Southern Red Sea), while HAB risks to desalination plants in winter months are low to moderate in Zone 2 (South Central Red Sea), and negligible in Zones 3 (North Central) and 4 (Northern).

Mitigating antibiotic pollution using cyanobacteria: Removal efficiency, pathways and metabolism

The occurrence of pharmaceuticals and personal care products (PPCPs) in wastewater poses huge environmental threats, even at trace concentrations, and novel approaches are urged due to the inefficiencies of conventional wastewater treatment plants, especially when processing contaminants at high concentrations. Meanwhile, another widespread problem in the aquatic domain is the occurrence of harmful algal blooms (HABs) which cause serious damage to the ecosystem, but have rarely been investigated for possible valorization. This study investigated the possibilities, mechanisms, and effects of toxin release of using a harmful cyanobacterial species, Microcystis aeruginosa (M. aeruginosa), in order to remove the widely used drug, tetracycline, at high concentration. The results were compared with the performance obtained by the use of the hitherto generally-selected chlorophyte alga Chlorella pyrenoidosa (C. pyrenoidosa) for tetracycline concentrations of 10-100 mg L-1. M. aeruginosa exhibited a much more effective and rapid tetracycline removal (over 98.0% removal in 2 days) than did C. pyrenoidosa (36.7%-93.9% in 2 days). A comprehensive kinetic investigation into probable removal pathways indicated that, theoretically, bio-remediation dominated the process by M. aeruginosa (71.6%), while only accounting for 20.5% by C. pyrenoidosa. Both microalgae promoted the hydrolysis of tetracycline under conditions of increased pH and inhibited abiotic photolytic reactions by the shading effect to the water column, when compared with control experiments. Although identical degradation by-products were identified from treatments by both microalgal species, distinct by-products were also confirmed, unique to each treatment. Moreover, the growth of M. aeruginosa biomass exhibited strong tolerance to tetracycline exposure and released significantly lower levels of microcystin-LR, compared with the control systems. This study supports the possibility of reusing HABs species for the effective remediation of antibiotics at high concentrations. We have further suggested possible mechanisms for remediation and demonstrated control of toxin release.

Metagenome-Assembled Genome Sequence of Dolichospermum circinale Strain Clear-D4, Assembled from a Harmful Cyanobacterial Bloom Enrichment Culture.

Dolichospermum circinale (formerly Anabaena circinale) is a significant harmful algal bloom species. We report the draft metagenome-assembled genome (MAG) for a strain of D. circinale (Clear-D4) obtained from an enrichment culture. The genome sequence comprises 5,029,933 bp in 560 contigs with a GC content of 37%.

Phytoplankton communities in two wide-open bays in the Iberian upwelling system

The main meteorological and oceanographic drivers shaping phytoplankton community structure and dynamics are investigated in two wide-open bays influenced by coastal upwelling. Local processes influencing the proliferation of harmful algal bloom species were also investigated. The work was developed during one year in Lisbon Bay (central-west coast) and in Lagos Bay (south coast), both located on the upwelling shadow of prominent headlands. In both bays, the results indicated a bi-modal annual pattern in phytoplankton biomass, and phytoplankton concentration maxima, between spring and late-summer, were associated with high diatom abundances. In Lagos Bay, higher dinoflagellate abundances were observed from spring to autumn, while in Lisbon Bay these were recorded from late-summer to autumn. The coccolithophores were a frequent group all year round in Lisbon Bay, which contrasts with Lagos Bay where they were the least frequent group. The phytoplankton community structure showed significant spatial and seasonal differences. The community succession pattern indicated the existence of four biological seasons in Lisbon Bay and at the offshore site in Lagos Bay. By contrast, the nearshore site in Lagos Bay was characterized by having no significant differences between summer and autumn. Differences in HAB species/groups were also observed between the bays. In general, HABs occurred at higher concentrations and were more persistent in Lagos Bay.In both bays, winter assemblages were influenced by water column mixing processes, although precipitation was also relevant in Lagos. Upwelling was a key driver of the spring phytoplankton community in Lagos Bay, while in Lisbon Bay other factors seemed to drive the spring phytoplankton assemblages. Both summer and autumn communities were related to thermal stratification. In autumn, the occurrence of reversal circulation patterns also played an important role in shaping the phytoplankton communities, especially in Lagos Bay. Overall, this study revealed differences on phytoplankton community patterns in two wide-open bays, shaped by the local environmental variables.

Algicidal Activity of Cyperus rotundus Aqueous Extracts Reflected by Photosynthetic Efficiency and Cell Integrity of Harmful Algae Phaeocystis globosa

Phaeocystis globosa is regarded as a notoriously harmful algal bloom species. Suppressing harmful algae using algicidal substances extracted from plants is considered an effective method. The physiological and biochemical processes of P. globosa were explored by exposure to different concentrations of aqueous extracts of Cyperus rotundus. All treatments indicated various inhibitory effects on the algal growth compared to the control samples without adding extracts. At 48 h, the 4, 8, and 16 mg/mL treatment groups showed a significant inhibitory effect, consistent with a decrease in the chlorophyll-a content and photosynthetic efficiency. The images of the transmission electron microscope (TEM) further confirmed that a subset of the cells in the treatment groups exhibited morphological anomalies. The algicidal active substances were mainly identified as phenolic acids containing maximal content of quinic acid in aqueous extracts according to the results of ultra-high-performance liquid chromatography-tandem time-of-flight mass spectrometer (UPLC-HRMS). The 50% anti-algal effect concentration of quinic acid was 22 mg/L at 96 h (EC50–96h). Thus, the phenolic acids might be considered as major inhibitors of the growth of P. globosa. These results demonstrated that the aqueous extracts of C. rotundus could potentially control the growth of P. globosa.

Development of a high-resolution molecular marker for tracking Phaeocystis globosa genetic diversity through comparative analysis of chloroplast genomes

The phytoplankton Phaeocystis globosa thrives in a wide range of marine regions and plays an important role in climate control. It can also form harmful algal blooms (HABs) that threaten environments and impact important coastal infrastructures. Mechanisms underlying the formation of P. globosa blooms still remain poorly understood. Accumulating evidence suggests that P. globosa has high genetic diversity and different P. globosa strains may have differential contributions to the development of P. globosa blooms. However, due to the lack of molecular markers with adequate resolution for distinguishing P. globosa genetic diversity, such differential contributions by different P. globosa strains could not be accurately ascertained. As such, high-resolution molecular markers need to be developed and applied to distinguish P. globosa genetic diversity. In this study, we undertook to define high-resolution molecular marker by assembling and comparing the whole chloroplast genomes of P. globosa strains isolated from different regions of the world. Through comparative analysis of P. globosa cpDNAs and detection of single nucleotide variations (SNVs), a molecular marker pgcp1 with improved resolution was developed. The pgcp1 demonstrated the highest resolution compared with other regions including 18S rDNA V4 region, 28S rDNA D1–D2 region and rbcL region, through genetic distance and phylogenetic analysis of 13 P. globosa strains. Molecular analysis of environmental samples and strains collected in multiple expeditions from a wide range of ocean regions including multiple regions in China, Vietnam, Thailand and Western Pacific using pgcp1 as the molecular marker displayed high genetic diversity of P. globosa with at least four major P. globosa clades. In conclusion, we have developed pgcp1 as a high-resolution molecular marker for the harmful algal bloom species P. globosa, which can be used to track intra-species genetic diversity and dynamics of P. globosa during bloom development.

Bioactivities of algicidal C18 hydroxy unsaturated fatty acid isolated from the red alga Tricleocarpa jejuensis and its synthesized propargylic derivative

(±)-(E)-12-hydroxyoctadec-10-enoic acid (compound A) was isolated from the red alga Tricleocarpa jejuensis in our previous study as a potent algicidal compound against red tide microalga Chattonella antiqua (Ochrophyta, Raphidophyceae). Interestingly, its propargylic derivative, 12-hydroxyoctadec-10-ynoic acid (compound B), which was obtained as a synthetic intermediate of compound A, showed an even more extensive algicidal activity. In this study, the effects of compound A and B on the major causative species of harmful algal blooms (HABs) such as Chattonella marina (Ochrophyta, Raphidophyceae), Heterocapsa circularisquama, and Karenia mikimotoi (Miozoa, Dinophyceae) in addition to C. antiqua were investigated. Both compounds exhibited toxic effects on these red tide flagellates in a concentration dependent manner with LC50 < 10 μg/mL, and the activities of compound B were much stronger than compound A. Zooplankton rotifer (Brachionys plicatilis) was relatively resistant to the compounds, and the lethal effects of H. circularisquama and K. mikimotoi on rotifers were reduced in the presence of compound A and B, suggesting their potential usage in the mitigation strategy for HABs. Consistent with the toxicities on the HAB species, compound B showed stronger cytotoxicity on HeLa, XC, and U937 cells than A. Since compound B but not compound A showed haemolytic activity on rabbit erythrocytes, specific action of compound B on cell membrane may be responsible for the potent cytotoxicity. Furthermore, compound B exhibited higher antibacterial effect on Staphylococcus aureus than compound A, while both were not effective on Enchiridia coli. Our results suggest that compound A and B are promising multifunctional candidates with potential to develop not only as anti-red tide microalgae but also as tumor cell-killing and antibacterial agents. This is the first report indicating that replacing a double bond in the hydroxy unsaturated fatty acid with a triple bond results in much augmentation of the bioactivities.

Thin layers of phytoplankton and harmful algae events in a coastal upwelling system

We combined time-series from a monitoring program and specific field observations in order to: 1) describe the characteristics of thin layers of phytoplankton (TLP) in the Galician Rías Baixas (NW Iberian Peninsula), 2) investigate the relationship between spatially-extended TLP (se-TLP) events and environmental variables, and 3) analyze the relationship between TLP occurrence and cell densities of toxin-producing harmful algal bloom (THAB) species. Between 2012 and 2015, a total of 118 TLP were detected in any of the 39 stations weekly sampled in the study area in the frame of the monitoring program, which represents a frequency of occurrence of 2%. Most TLP (84%) were detected between May-August and located slightly below shallow pycnoclines. Eight se-TLP events, i.e., when at least five stations were simultaneously influenced by the occurrence of a TLP, were identified during the period 2012–2015. Six out eight of these events happened during summer-upwelling conditions, and according to a Principal Component Analysis (PCA) they were positively correlated with thermal stratification. The other two events, detected during spring-downwelling, were positively correlated with haline stratification. A logistic regression model including six variables (surface temperature, relative humidity, bottom salinity, a proxy for the intrusion of the Miño River plume into Ría de Vigo, Miño River flow, and bottom temperature) explained 42% of the variance in the occurrence of se-TLP events. The temporal persistence of TLP events was confirmed by observations carried out during specific cruises, which showed how TLP were formed and disappeared over short periods of time in response to changes in vertical mixing. TLP were more frequently observed in Ría de Pontevedra, which was characterized by longer harvesting closures due to detection of Dinophysis toxins (DSP: diarrhetic shellfish poisoning toxins and pectenotoxins) above regulatory levels. About 25% of the TLP detected in the Rías Baixas were associated with increased cell densities of potentially toxic Pseudo-nitzschia species (ASP: amnesic shellfish poisoning) and of D. acuminata. These results suggest that a relationship may be established between the occurrence of TLP and the growth and/or accumulation of the main THAB species in the Galician Rías Baixas.

Distribution of Harmful Algal Growth-Limiting Bacteria on Artificially Introduced Ulva and Natural Macroalgal Beds

The intensity and frequency of harmful algal blooms (HABs) have increased, posing a threat to human seafood resources due to massive kills of cultured fish and toxin contamination of bivalves. In recent years, bacteria that inhibit the growth of HAB species were found to be densely populated on the biofilms of some macroalgal species, indicating the possible biological control of HABs by the artificial introduction of macroalgal beds. In this study, an artificially created Ulva pertusa bed using mobile floating cages and a natural macroalgal bed were studied to elucidate the distribution of algal growth-limiting bacteria (GLB). The density of GLB affecting fish-killing raphidophyte Chattonella antiqua, and two harmful dinoflagellates, were detected between 106 and 107 CFU g−1 wet weight on the biofilm of artificially introduced U. pertusa and 10 to 102 CFU mL−1 from adjacent seawater; however, GLB found from natural macroalgal species targeted all tested HAB species (five species), ranging between 105 and 106 CFU g−1 wet weight in density. These findings provide new ecological insights of GLB at macroalgal beds, and concurrently demonstrate the possible biological control of HABs by artificially introduced Ulva beds.

The mechanism of a new type of modified clay controlling Phaeocystis globosa growth

Phaeocystis globosa is a harmful algal bloom (HAB) species worldwide. Using modified clay (MC) to control HABs and to mitigate their adverse effects is currently a commonly used method in China. In this paper, the effects of oxidized composite modified clay (OXI-MC) on P. globosa were studied from different perspectives. The results show that the OXI-MC could effectively remove P. globosa and inhibit both the growth of residual algal cells and the formation of new colonies. The P. globosa algal biomass removal efficiencies after 3 h reached 90% at a dose of 0.1 g/L, and the number of colonies with different particle sizes was greatly reduced. Compared with those of the control, the superoxide dismutase (SOD) activity, catalase (CAT) activity, and malondialdehyde (MDA) content of the residual algae significantly increased, indicating that OXI-MC caused oxidative stress in the algal cells. In addition, we evaluated the effects of OXI-MC on the photosynthesis of residual microalgae and found that the maximal photochemical efficiency of photosystem II (PSII) under dark adaptation (Fv/Fm) and actual photochemical efficiency of PSII (ΦPSII) decreased, severely damaging the photosynthesis efficiency, implying that OXI-MC effected the photosynthesis system of P. globosa. The results of this study clarify that OXI-MC could remove the most of algal cells and break up the colonies of P. globosa by collision, flocculation, and releasing active substances, as well as inhibit effectively the growth and colony formation of residual P. globosa by causing oxidative stress, reducing photosynthesis activity, accelerating the degradation of polysaccharides, and inhibiting the formation of colonies.

Quantitative PCR assay for the simultaneous identification and enumeration of multiple Karenia species.

Quantitative PCR (qPCR) is the method of choice for specific detection and quantification of harmful algal bloom (HAB) species. Development of qPCR assay for simultaneous enumeration of species that frequently co-exist in HABs is required. A high sensitivity TaqMan qPCR assay, using probe and primers, located at ITS1-5.8S-ITS2 rDNA region, detecting, specifically, Karenia selliformis, K. bidigitata, and K. mikimotoi, was designed. ITS1-5.8S-ITS2 rDNA region copy numbers per Karenia cell genome were estimated to 217.697 ± 67.904, allowing cell quantification. An application of the designed methodology in field samples has been conducted, and it showed high sensitivity (detection of around 10-1 cell/100 mg of bivalve mollusk tissue, equivalent to about 20 copies of the target sequence). We suggest that the optimized method could contribute to early detection of three closely related Karenia species in seafood cultivating areas to promote control quality, guarantee a fast and effective intervention, and improve public health prevention.

Cell density-dependent suppression on the development and photosynthetic activities of Sargassum fusiformis embryos by dinoflagellate Karenia mikimotoi

Lots of research has demonstrated that macroalgae can strongly inhibit the growth of harmful algal bloom (HAB) species in general. However, the effects of HABs or HAB-forming species on macrophytes are still largely uncharacterized until now. In the present study, the effects of the dinoflagellate Karenia mikimotoi cell density gradient, live cell suspension (LC), ruptured cell suspension (RC) as well as the cell-free supernatant (FC) of K. mikimotoi at 1000 μg Chla l−1 (~1.0 × 105 cells ml−1) on the development and photosynthesis of Sargassum fusiforme embryos were investigated in a series of laboratory experiments. The results showed that co-cultivation with K. mikimotoi at 500 μg Chla l−1(~5.0 × 104 cells ml−1) and higher cell densities significantly (P<0.05) inhibited the development, pigment content and photosynthetic activities of the embryos. In addition, the inhibitory effects increased with increased cell densities and prolonged exposure time. Compared to the embryos cultured with the F/2 medium (Control), exposure to LC, RC and FC of K. mikimotoi at 1000 μg Chla l−1for 2 weeks all led to decreased relative growth rate (RGR), chlorophyll (Chl) a content, carotenoids (Car) content and photosynthetic activities of the embryos, with LC and RC exhibiting the maximal and the minimal suppression. The dominant inhibitory effects of FC on the embryos indicated that the suppression was mainly caused by the allelochemicals, while the slightest inhibitory effects of RC on the embryos suggested that some intracellular growth-promoting substances were synchronously released when K. mikimotoi cells lyzed. In addition, the most severe growth suppression of embryos by LC indicated that intact cell contact by K. mikimotoi probably also contributed to the inhibitory effects. These results indicated that a dense HAB formed by K. mikimotoi could seriously suppress the development and photosynthesis of S. fusiforme embryos and eventually reduce the seedlings stock.

Seasonal variations of phytoplankton assemblages in relation to environmental factors in Mediterranean coastal waters of Morocco, a focus on HABs species

Studies on phytoplankton and in particular Harmful Algal Blooms (HABs) species in southern Mediterranean waters are scarce. We performed from April 2008 to June 2009 weekly investigations on microphytoplankton community structure and abundance in two contrasted marine ecosystems located in the western Moroccan Mediterranean coast, M'diq Bay and Oued Laou Estuary. Simultaneously, we measured the main physico-chemical parameters. Globally, the two studied areas showed comparable values of the assessed abiotic environmental factors. Temperature and salinity followed seasonal variation with values ranging from 13.5 °C to 21.4 °C and 31 to 36.8, respectively. Average nutrient values in surface water ranged from 0.7 to 45.76 μM for dissolved inorganic nitrogen, 0.02–2.10 μM for PO4 and 0.23–17.46 μM for SiO4 in the study areas. A total of 92 taxa belonging to 8 taxonomic classes were found. The highest number of microphytoplankton abundance reached 1.2 × 106 cells L−1 with diatoms being the most abundant taxa. Factorial Discriminant Analysis (FDA) and Spearman correlation test showed a significant seasonal discrimination of dominant microphytoplankton species. These micro-organisms were associated with different environmental variables, in particular temperature and salinity. Numerous HABs species were encountered regularly along the year. Although Dinophysis species and Prorocentrum lima were present in both sites, no Lipophilic Shellfish Poisoning was detected for the analyzed bivalve mollusks. Domoic acid (DA), produced by toxic species of Pseudo-nitzschia was found with concentrations up to 18 µg DA g−1 in the smooth clam Callista chione. Data showed that the observed persistent and dramatic Paralytic Shellfish Poisoning (PSP) intoxication of mollusks resulted probably of Gymnodinium catenatum proliferations in both studied areas. Contrary to C. chione, the cockle Achanthocardia tuberculatum showed a permanent and extremely high toxicity level during the 15 months survey with up to 7545 µg Equivalent Saxitoxin kg−1 flesh (ten times higher than the sanitary threshold of 800 µg eqSTX Kg−1flesh). The present work highlights for the first time the dynamic of microphytoplankton including HABs species and their associated toxin accumulation in the commercially exploited shellfish in the southern western Mediterranean waters of Morocco. Furthermore, the acquired data will help us to improve the monitoring of HABs species and related toxins in these coastal marine systems.

Current and Future Remote Sensing of Harmful Algal Blooms in the Chesapeake Bay to Support the Shellfish Industry

Harmful algal bloom (HAB) species in the Chesapeake Bay can negatively impact fish, shellfish, and human health via the production of toxins and the degradation of water quality. Due to the deleterious effects of HAB species on economically and environmentally important resources, such as oyster reef systems, Bay area resource managers are seeking ways to monitor HABs and water quality at large spatial and fine temporal scales. The use of satellite ocean color imagery has proven to be a beneficial tool for resource management in other locations around the world where high-biomass, nearly monospecific HABs occur. However, remotely monitoring HABs in the Chesapeake Bay is complicated by the presence of multiple, often co-occurring, species and optically-complex waters. Here we present a summary of common marine and estuarine HAB species found in the Chesapeake Bay, Alexandrium monilatum, Karlodinium veneficum, Margalefidinium polykrikoides, and Prorocentrum minimum, that have been detected from space using multispectral data products from the Ocean and Land Color Imager (OLCI) sensor on the Sentinel-3 satellites and identified based on historic phytoplankton data, in situ sampling, and ecological associations. We review how future hyperspectral instruments will improve discrimination of potentially harmful species from other phytoplankton communities and present a framework in which satellite data products could aid Chesapeake Bay resource managers with monitoring water quality and protecting shellfish resources.

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.

Algicidal properties of fermentation products from Bacillus cereus strain JZBC1 dissolving dominant dinoflagellate species Scrippsiella trochoidea, Prorocentrum micans, and Peridinium umbonatum

Intensive and semi-intensive aquaculture systems typically produce high loads of nutrients in their discharge, potentially leading to the development and persistence of harmful algal blooms (HABs). Algicidal bacteria, which inhibit algal growth or kill algal cells, offer a promising biocontrol strategy for reducing HAB. The strain JZBC1, which displays strong algicidal activity against the HAB species Scrippsiella trochoidea, was previously isolated from a dinoflagellate bloom area and identified as Bacillus cereus. In this study, strain JZBC1 was fermented in 2 L and 50 L systems, and then, algicidal properties of JZBC1 fermentation products on the harmful dinoflagellate species S. trochoidea, Prorocentrum micans, and Peridinium umbonatum were examined. Bacterial concentrations of strain JZBC1 reached 6.23 × 109 and 4.47 × 109 CFU/mL in 2 L and 50 L cultures, respectively, and thus effectively expanded during fermentation. Strain JZBC1 showed substantial algicidal activities and a wide algicidal range toward harmful dinoflagellates. Vegetative JZBC1 cells exhibited the best inhibitory and algicidal effects in 1 day. Strain JZBC1 can be formulated into a powder, and the spores can be activated before field application to increase their efficacy. These findings will facilitate large-scale fermentation production and application of Bacillus strain JZBC1 for controlling dinoflagellate blooms in aquaculture ponds.