Detection of Karenia brevis blooms on the west Florida shelf using in situ backscattering and fluorescence data

Using shipboard data collected from the central west Florida shelf (WFS) between 2000 and 2001, an optical classification algorithm was developed to differentiate toxic Karenia brevis blooms (>10⁴ cells l⁻¹) from other waters (including non-blooms and blooms of other phytoplankton species). The identification of K. brevis blooms is based on two criteria: (1) chlorophyll a concentration ≥1.5 mg m⁻³ and (2) chlorophyll-specific particulate backscattering at 550 nm ≤ 0.0045 m² mg⁻¹. The classification criteria yielded an overall accuracy of 99% in identifying both K. brevis blooms and other waters from 194 cruise stations. The algorithm was validated using an independent dataset collected from both the central and south WFS between 2005 and 2006. After excluding data from estuarine and post-hurricane turbid waters, an overall accuracy of 94% was achieved with 86% of all K. brevis bloom data points identified successfully. Satisfactory algorithm performance (88% overall accuracy) was also achieved when using underway chlorophyll fluorescence and backscattering data collected during a repeated alongshore transect between Tampa Bay and Florida Bay in 2005 and 2006. These results suggest that it may be possible to use presently available, commercial optical backscattering instrumentation on autonomous platforms (e.g. moorings, gliders, and AUVs) for rapid and timely detection and monitoring of K. brevis blooms on the WFS.     

The influence of bloom intensity on the encystment rate and persistence of Alexandrium minutum in Cork Harbor,Ireland

Toxic Alexandrium minutum blooms recur annually in Cork Harbor, Ireland where they initiate in an inlet known as the North Channel. The dynamics of these blooms have been studied since 2003, and a high degree of inter-annual variability in the cell densities has been observed. Two intense blooms, with maximum cell densities >500,000 cells L⁻¹, were observed in the summers of 2004 and 2011. Annual cyst surveys during winter found that cyst densities decreased after the 2004 bloom, and by 2010 an average of ca. 40 cysts g dry wt sediment⁻¹ was recorded. The intensity of blooms was found to be independent of the cyst density measured the previous winter. The cyst input to the sediment during both intense and low density blooms was measured directly through the deployment of sediment traps in the North Channel. The data allowed an estimate of the proportion of the A. minutum vegetative cells that underwent successful encystment, which averaged at 2.5% across a range of cell densities spanning three orders of magnitude. Maturation times of fresh cysts were determined at 5, 10 and 15 °C. The maturation time at 15 °C was found to be approximately 5 months, a value which increased by two months for a 5° decrease in temperature. A cyst dynamics model was constructed based on the field data to simulate the temporal variation of A. minutum cysts in the oxic layer of sediment. It revealed that a degree of resuspension is required to prevent cyst stocks from becoming exhausted in the thin oxic layer at the surface of the sediment. The model also demonstrated that the cysts supplied by periodic intense blooms, which occur with a frequency of every 7–8 years, are not in themselves enough to allow the population to persist over long time scales (decades). The cyst input from interim blooms of lower density is however enough to ensure the annual inoculation of the water column with A. minutum cells.     

The potential role of anthropogenically derived nitrogen in the growth of harmful algae in California,USA

Cultural eutrophication is frequently invoked as one factor in the global increase in harmful algal blooms, but is difficult to definitively prove due to the myriad of factors influencing coastal phytoplankton bloom development. To assess whether eutrophication could be a factor in the development of harmful algal blooms in California (USA), we review the ecophysiological potential for urea uptake by Pseudo-nitzschia australis (Bacillariophyceae), Heterosigma akashiwo (Raphidophyceae), and Lingulodinium polyedrum (Dinophyceae), all of which have been found at bloom concentrations and/or exhibited noxious effects in recent years in California coastal waters. We include new measurements from a large (Chlorophyll a > 500 mg m⁻³) red tide event dominated by Akashiwo sanguinea (Dinophyceae) in Monterey Bay, CA during September 2006. All of these phytoplankton are capable of using nitrate, ammonium, and urea, although their preference for these nitrogenous substrates varies. Using published data and recent coastal time series measurements conducted in Monterey Bay and San Francisco Bay, CA, we show that urea, presumably from coastal eutrophication, was present in California waters at measurable concentrations during past harmful algal bloom events. Based on these observations, we suggest that urea uptake could potentially sustain these harmful algae, and that urea, which is seldom measured as part of coastal monitoring programs, may be associated with these harmful algal events in California.     

Alexandrium pacificum Litaker sp. nov (Group IV): Resting cyst distribution and toxin profile of vegetative cells in Bizerte Lagoon (Tunisia,Southern Mediterranean Sea)

A high spatial resolution sampling of Alexandrium pacificum cysts, along with sediment characteristics (% H₂O, % organic matter (OM), granulometry), vegetative cell abundance and environmental factors were investigated at 123 study stations in Bizerte Lagoon (Tunisia). Morphological examination and ribotyping of cells obtained from a culture called ABZ1 obtained from a cyst isolated in lagoon sediment confirmed that the species was A. pacificum. The toxin profile from the ABZ1 culture harvested during exponential growth phase was simple and composed of the N-sulfocarbamoyl toxins C1 (9.82 pg toxin cell⁻¹), the GTX6 (3.26 pg toxin cell⁻¹) and the carbamoyl toxin Neo-STX (0.38 pg toxin cell⁻¹). The latter represented only 2.8% of the total toxins in this strain.High abundance of A. pacificum cysts correlated with enhanced percentages of water and organic matter in the sediment. In addition, sediment fractions of less than 63 μm were examined as a favorable potential seedbed for initiation of future blooms and outbreaks of A. pacificum in the lagoon. A significant difference in the cyst distribution pattern was recorded among the lagoon's different zones, with the higher cyst abundance occurring in the inner waters. Also, no correlation due to the specific hydrodynamics of the lagoon was observed in the spatial distribution of A. pacificum cysts and vegetative cells.     

Toxicity studies of Trichodesmium erythraeum (Ehrenberg, 1830) bloom extracts,from Phoenix Bay,Port Blair,Andamans

Occurrence of toxic cyanobacterial blooms has become a worldwide problem, increasing the risk of human poisoning due to consumption of seafood contaminated with cyanotoxins. Though no such cases of human intoxication due to toxic blooms have been reported so far from India, most of the studies related to blooms have been restricted to reporting of a bloom and/or antimicrobial activity of its extract. Detailed toxicity study of cyanobacterial blooms are lacking. A study on the toxicity of a dense bloom (14.56 × 10⁶ trichomes L⁻¹) of the marine diazotrophic cyanobacteria, Trichodesmium erythraeum, observed in the coastal waters of Phoenix Bay, Port Blair, Andamans was undertaken. The significance of this bloom is that it was a single species and had conspicuously inhibited the growth of other phytoplankton and complete exclusion of zooplankton from the bloom region, intimating the involvement of toxins in the bloom. The cyanobacterial extracts showed prominent antimicrobial activity against certain human pathogenic bacteria and fungi. Studies on the toxicity of the cyanobacterial extracts was carried out using brine shrimp bioassay, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and comet assay. The cyanobacterial extract exhibited toxic effect to Artemia salina causing mortality of up to 40% after 48 h at a concentration of 1 mg mL⁻¹, while it induced cytotoxicity in cell lines (HepG2 and HaCat) and caused DNA damage in human lymphocytes in vitro.     

The emergence of Dinophysis acuminata blooms and DSP toxins in shellfish in New York waters

The dynamics of Dinophysis acuminata and its associated diarrhetic shellfish poisoning (DSP) toxins, okadaic acid (OA) and dinophysistoxin-1 (DTX1) as well as pectenotoxins (PTXs), were investigated within plankton and shellfish in Northport Bay, NY, USA, over a four year period (2008–2011). Over the course of the study, Dinophysis bloom densities ranged from ~10⁴ to 10⁶ cells L⁻¹ and exceeded 10⁶ L⁻¹ in 2011 when levels of total OA, total DTX1, and PTX in the water column were 188, 86, and 2900 pg mL⁻¹, respectively, with the majority of the DSP toxins present as esters. These cell densities exceed – by two orders of magnitude – those previously reported within thousands of samples collected from NY waters from 1971 to 1986. The bloom species was positively identified as D. acuminata via scanning electron microscopy and genetic sequencing (cox1 gene). The cox1 gene sequence from the D. acuminata populations in Northport Bay was 100% identical to D. acuminata from Narragansett Bay, RI, USA and formed a strongly supported phylogenetic cluster (posterior probability = 1) that included D. acuminata and Dinophysis ovum from systems along the North Atlantic Ocean. Shellfish collected from Northport Bay during the 2011 bloom had DSP toxin levels (1245 ng g⁻¹ total OA congeners) far exceeding the USFDA action level (160 ng g⁻¹ total OA of shellfish tissue) representing the first such occurrence on the East Coast of the U.S. D. acuminata blooms co-occurred with paralytic shellfish poisoning (PSP) causing blooms of Alexandrium fundyense during late spring each year of the study. D. acuminata cell abundances were significantly correlated with levels of total phytoplankton biomass and Mesodinium spp., suggesting food web interactions may influence the dynamics of these blooms. Given that little is known regarding the combined effects of DSP and PSP toxins on human health and the concurrent accumulation and depuration of these toxins in shellfish, these blooms represent a novel managerial challenge.     

Newly discovered role of the heterotrophic nanoflagellate Katablepharis japonica,a predator of toxic or harmful dinoflagellates and raphidophytes

Heterotrophic nanoflagellates are ubiquitous and known to be major predators of bacteria. The feeding of free-living heterotrophic nanoflagellates on phytoplankton is poorly understood, although these two components usually co-exist. To investigate the feeding and ecological roles of major heterotrophic nanoflagellates Katablepharis spp., the feeding ability of Katablepharis japonica on bacteria and phytoplankton species and the type of the prey that K. japonica can feed on were explored. Furthermore, the growth and ingestion rates of K. japonica on the dinoflagellate Akashiwo sanguinea—a suitable algal prey item—heterotrophic bacteria, and the cyanobacteria Synechococcus sp., as a function of prey concentration were determined. Among the prey tested, K. japonica ingested heterotrophic bacteria, Synechococcus sp., the prasinophyte Pyramimonas sp., the cryptophytes Rhodomonas salina and Teleaulax sp., the raphidophytes Heterosigma akashiwo and Chattonella ovata, the dinoflagellates Heterocapsa rotundata, Amphidinium carterae, Prorocentrum donghaiense, Alexandrium minutum, Cochlodinium polykrikoides, Gymnodinium catenatum, A. sanguinea, Coolia malayensis, and the ciliate Mesodinium rubrum, however, it did not feed on the dinoflagellates Alexandrium catenella, Gambierdiscus caribaeus, Heterocapsa triquetra, Lingulodinium polyedra, Prorocentrum cordatum, P. micans, and Scrippsiella acuminata and the diatom Skeletonema costatum. Many K. japonica cells attacked and ingested a prey cell together after pecking and rupturing the surface of the prey cell and then uptaking the materials that emerged from the ruptured cell surface. Cells of A. sanguinea supported positive growth of K. japonica, but neither heterotrophic bacteria nor Synechococcus sp. supported growth. The maximum specific growth rate of K. japonica on A. sanguinea was 1.01 d⁻¹. In addition, the maximum ingestion rate of K. japonica for A. sanguinea was 0.13 ng C predator⁻¹d⁻¹ (0.06 cells predator⁻¹d⁻¹). The maximum ingestion rate of K. japonica for heterotrophic bacteria was 0.019 ng C predator⁻¹d⁻¹ (266 bacteria predator⁻¹d⁻¹), and the highest ingestion rate of K. japonica for Synechococcus sp. at the given prey concentrations of up to ca. 10⁷ cells ml⁻¹ was 0.01 ng C predator⁻¹d⁻¹ (48 Synechococcus predator⁻¹d⁻¹). The maximum daily carbon acquisition from A. sanguinea, heterotrophic bacteria, and Synechococcus sp. were 307, 43, and 22%, respectively, of the body carbon of the predator. Thus, low ingestion rates of K. japonica on heterotrophic bacteria and Synechococcus sp. may be responsible for the lack of growth. The results of the present study clearly show that K. japonica is a predator of diverse phytoplankton, including toxic or harmful algae, and may also affect the dynamics of red tides caused by these prey species.     

In situ and satellite observations of a harmful algal bloom and water condition at the Pearl River estuary in late autumn 1998

Harmful algal blooms (HABs) have posed a serious threat to the aquaculture and fisheries industries in recent years, especially in Asia. During 1998 there were several particularly serious blooms in the coastal waters of south China, which caused a serious damage to aquaculture. We report a massive dinoflagellate bloom near the mouth of Pearl River in November 1998 with analyses of data from both in situ sea water measurements and satellites. A multi-parameter environmental mapping system was used to obtain real-time measurements of water quality properties and wind data through the algal bloom area, which allow us to compare water measurements from inside and outside of the bloom areas. This bloom with high concentrations of algal cells was evident as a series of red colored parallel bands of surface water that were 100–300 m long and 10–30 m wide with a total area of about 20–30 km² by visual. The algal density reached 3.8×10⁷ cells l⁻¹ and the surface chlorophyll-a (Chl-a) concentration was high. The algal species has been identified as Gymnodinium cf. catenatum Graham. The water column in the bloom area was stratified, where the surface temperature was 24–25 °C, the salinity was 18–20%, and the northern wind was about 3–4 m s⁻¹ in the bloom area. The SeaWiFS image has shown high Chl-a area coinciding with the bloom area. The sea surface temperature (SST) image of the Pearl River estuary combined with the in situ measurements indicated that the bloom occurred along a mixing front between cooler lower salinity river water and warmer higher saline South China Sea (SCS) water.     

Bloom formation potential in the harmful dinoflagellate Akashiwo sanguinea: Clues from movement behaviors and growth characteristics

We measured the growth rates and swimming behaviors of recently isolated strains of the dinoflagellate Akashiwo sanguinea to investigate to what degree growth and motility could contribute to the formation of in situ blooms. To quantify the effect of variation in in situ conditions on population growth rate, we applied two temperature treatments (10 °C and 20 °C) and measured growth in still conditions and on a shaker table, to emulate mild turbulence. To quantify the importance of intra-strain variability and trait variation in the species growth potential and vertical distribution, we included six strains isolated from a spatially and temporally extensive bloom on the US West Coast. Overall, as reported previously, A. sanguinea was observed to tolerate conditions amounting to a broad ecological niche with intra-specific variability further broadening tolerable conditions. In agreement with prior observations of slow growth rates of the species, average growth rates across all strains increased significantly from 0.12 d⁻¹ (±0.03) at 10 °C to 0.28 d⁻¹ (±0.13) at 20 °C in still conditions. Contrary to prior reports, mild turbulence had neutral or positive effects on most strains’ growth rates, with one strain only able to grow on the shaker table. Growth rates in mild turbulence were higher than in still conditions and increased from 0.15 d⁻¹ (±0.01) at 10 °C to 0.43 d⁻¹ (± 0.04) at 20 °C. There was significant intra-strain variation in growth rates (>50% coefficient of variation) and movement behaviors. All strains had both up and down swimming fractions, leading to predictions of vertically patchy distributions, rather than surface aggregations. Slow growth rates and dispersive swimming behaviors suggest in situ mortality must be low and tolerance of seasonally varying water temperatures lead to accumulation and persistence of cells over months and kilometers. Estimates of in situ loss rates are a critical but missing component of identifying the bloom formation mechanisms of this species.     

Evaluation of the effects of light intensity on growth of the benthic dinoflagellate Ostreopsis sp. 1 using a newly developed photoirradiation-culture system and a novel regression analytical method

Benthic dinoflagellates of the genus Ostreopsis are found all over the world in temperate, subtropical, and tropical coastal regions. Our recent studies revealed that a putative “cryptic” species of Ostreopsis ovata is present widely along Japanese coasts. This organism, Ostreopsis sp. 1, possesses palytoxin analogs and thus its toxic blooms may be responsible for potential toxification of marine organisms. To evaluate the bloom dynamics of Ostreopsis sp. 1, the present study examined the growth responses of Ostreopsis sp. 1 strain s0716 to various light intensities (photon flux densities: μmol photons m⁻² s⁻¹) using a newly devised photoirradiation-culture system. This novel system has white light-emitting diodes (LEDs) capable of more closely simulating the wavelength spectrum of light entering the oceanic water column than do fluorescent tubes and halogen lamps. In this system, the light intensity of the white LEDs was reduced through two polarizing filters by varying the rotation angles of the filters. Thereby, the new system was capable of culturing microalgae under well-controlled light intensity conditions. Ostreopsis sp. 1 grew proportionally when light intensity was increased from 49.5 to 199 μmol photons m⁻² s⁻¹, but its growth appeared to be inhibited slightly at ≥263 μmol photons m⁻² s⁻¹. The relationship between observed growth rates and light intensity was calculated at R > 0.99 (P < 0.01) using a regression analysis with a modified equation of the photosynthesis-light intensity (P-L) model. The equation determined the critical light intensities for growth of Ostreopsis sp. 1 and the organism's growth potential as follows: (1) the threshold light intensity for growth: 29.8 μmol photons m⁻² s⁻¹; (2) the optimum light intensity (L_m) giving the maximum growth rate (μ_max = 0.659 divisions day⁻¹): 196 μmol photons m⁻² s⁻¹; (3) the optimum light intensity range (L_opt) giving ≥95% μ_max: 130–330 μmol photons m⁻² s⁻¹; (4) the semi-optimum range (L_sopt) giving ≥80% μ_max: 90 to over 460 μmol photons m⁻² s⁻¹. The L_sopt represents 4.5–23% ambient light intensity present in surface waters off of a temperate region of the Japanese coast, Tosa Bay; putatively, this semi-optimum range of light intensity appears at depth of 12.9–27.8 m. Considering these issues, our data indicate that Ostreopsis sp. 1 in coastal environments may form blooms at ca. ∼28 m depth in regions along Japanese coasts.     

Allelopathic effects of Microcystis aeruginosa on green algae and a diatom: Evidence from exudates addition and co-culturing

Allelopathic interactions among phytoplankton species are regarded as one of the important factors contributing to phytoplankton species competition and succession. The role and extent of allelopathic effects of blooming freshwater cyanobacteria on other phytoplankton species in eutrophied waters, however, are still unknown. We examined the allelopathic effect of Microcystis aeruginosa on two common green algae (Scenedesmus quadricauda, Chlorella pyrenoidosa) and a diatom (Cyclotella meneghiniana) by adding exudates from different growth phases and in co-culture tests. Exudates of M. aeruginosa from the exponential growth phase and the stationary phase significantly inhibited the growth of S. quadricauda, C. pyrenoidosa and C. meneghiniana, whereas those from the decline phase increased their growth. The presence of M. aeruginosa extremely inhibited the growth of all tested species in co-cultures within 24 h. Our results indicate that under the tested environmental conditions (25 °C, light 80 μmol quanta m⁻² s⁻¹, manual shaking twice a day), allelopathic effects of M. aeruginosa on other phytoplankton species can significantly contribute to their competitive success.     

The relationship between Pseudo-nitzschia (Peragallo) and domoic acid in Scottish shellfish

The diatom genus Pseudo-nitzschia (Peragallo) associated with the production of domoic acid (DA), the toxin reposnsible for amnesic shellfish poisoning, is abundant in Scottish waters. A two year study examined the relationship between Pseudo-nitzschia cells in the water column and DA concentration in blue mussels (Mytilus edulis) at two sites, and king scallops (Pecten maximus) at one site. The rate of DA uptake and depuration differed greatly between the two species with M. edulis whole tissue accumulating and depurating 7 μg g⁻¹ (now expressed as mg kg⁻¹) per week. In contrast, it took 12 weeks for DA to depurate from P. maximus gonad tissue from a concentration of 68 μg g⁻¹ (now mg kg⁻¹) to <20 μg g⁻¹ (now mg kg^‐1). The DA depuration rate from P. maximus whole tissue was <5% per week during both years of the study. Correlations between the Pseudo-nitzschia cell densities and toxin concentrations were weak to moderate for M. edulis and weak for P. maximus. Seasonal diversity on a species level was observed within the Pseudo-nitzschia genus at both sites with more DA toxicity associated with summer/autumn Pseudo-nitzschia blooms when P. australis was observed in phytoplankton samples. This study reveals the marked difference in DA uptake and depuration in two shellfish species of commercial importance in Scotland. The use of these shellfish species to act as a proxy for DA in the environment still requires investigation.     

Inorganic and organic nitrogen uptake by the toxigenic diatom Pseudo-nitzschia australis (Bacillariophyceae)

The nitrogen uptake capabilities of the toxigenic diatom Pseudo-nitzschia australis (Frenguelli), freshly isolated from Monterey Bay California, were examined in unialgal laboratory cultures at saturating photosynthetic photon flux densities (100 μmol photons m⁻² s⁻¹) and 15 °C. The kinetics of nitrogen (nitrate, ammonium, urea and glutamine) uptake as a function of substrate concentration were estimated from short (20.5 min) incubations using the ¹⁵N-tracer technique. Based on the estimated maximum specific uptake rates and measures of N affinity (the initial slope of the uptake versus nutrient concentration curve), nitrate is the preferred nitrogen substrate, followed by glutamine and ammonium, which are equivalent. Rates of urea uptake by P. australis did not saturate at concentrations as high as 36 μg-at N L⁻¹, and urea uptake as a function of concentration could not be described by Michaelis–Menten kinetics over the concentration gradient tested. Although there is a clear preference for nitrate at equivalent concentrations (compared to ammonium, urea, and glutamine), these laboratory results demonstrate the capability of this pennate diatom to utilize both inorganic and organic forms of nitrogen, supporting field observations that P. australis blooms during both upwelling and non-upwelling conditions off the west coast of North America. Substantial differences in the nitrogenous nutrition of P. australis can be expected in these environments, and anthropogenic inputs of N substrates such as ammonium and urea can support its growth, and may contribute significantly to both harmful diatom blooms and the maintenance of seed populations at non-bloom abundances, particularly during periods of reduced or absent upwelling.     

Abundance and distribution of Ulva microscopic propagules associated with a green tide in the southern coast of the Yellow Sea

The presence of Ulva microscopic propagules may play an important role in the rapid development of high-biomass blooms of green algae in the Yellow Sea. Six cruises were conducted, to determine the abundance and distribution of Ulva microscopic propagules associated with a green tide that developed in the southern coastal waters of the Yellow Sea from April to August, 2012. Results indicated that Ulva microscopic propagules were widespread in these waters, with the highest density being up to 4800 ind. L⁻¹, prior to the appearance of the green tide in April. High densities were also widely distributed along the coast during May and June, after the appearance of the floating green tide. The quantity of Ulva microscopic propagules significantly decreased when the floating green tide declined in July, reaching densities of up to 162 ind. L⁻¹, following the disappearance of the floating green tide in August. Quantitative studies on the distribution patterns of Ulva microscopic propagules along the southern coast of the Yellow Sea indicated a significant correlation between density and salinity, turbidity and nutrient concentrations. Temporal and geographical distribution patterns of Ulva microscopic propagules were also significantly affected by the presence of a large biomass of attached, or floating, Ulva species algae.     

Climate variability and Dinophysis acuta blooms in an upwelling system

Dinophysis acuta is a frequent seasonal lipophilic toxin producer in European Atlantic coastal waters associated with thermal stratification. In the Galician Rías, populations of D. acuta with their epicentre located off Aveiro (northern Portugal), typically co-occur with and follow those of Dinophysis acuminata during the upwelling transition (early autumn) as a result of longshore transport. During hotter than average summers, D. acuta blooms also occur in August in the Rías, when they replace D. acuminata. Here we examined a 30-year (1985–2014) time series of D. acuta from samples collected by the same method in the Galician Rías. Our main objective was to identify patterns of distribution and their relation with climate variability, and to explain the exceptional summer blooms of D. acuta in 1989–1990. A dome-shaped relationship was found between summer upwelling intensity and D. acuta blooms; cell maxima were associated with conditions where the balance between upwelling intensity and heating, leading to deepened thermoclines, combined with tidal phase (3 days after neap tides) created windows of opportunity for this species. The application of a generalized additive model based on biological (D. acuta inoculum) and environmental predictors (Cumulative June–August upwelling CUI_JJA, average June–August SST_JJA and tidal range) explained more than 70% of the deviance for the exceptional summer blooms of D. acuta, through a combination of moderate (35,000–50,000 m³ s⁻¹ km⁻¹) summer upwelling (CUI_JJA), thermal stratification (SST_JJA > 17 °C) and moderate tidal range (∼2.5 m), provided D. acuta cells (inoculum) were present in July. There was no evidence of increasing trends in D. acuta bloom frequency/intensity nor a clear relationship with NAO or other long-term climatic cycles. Instead, the exceptional summer blooms of 1989–1990 appeared linked to extreme hydroclimatic anomalies (high positive anomalies in SST and NAO index), which affected most of the European Atlantic coast.     

Germination fluctuation of toxic Alexandrium fundyense and A. pacificum cysts and the relationship with bloom occurrences in Kesennuma Bay,Japan

While cyst germination may be an important factor for the initiation of harmful/toxic blooms, assessments of the fluctuation in phytoplankton cyst germination, from bottom sediments to water columns, are rare in situ due to lack of technology that can detect germinated cells in natural bottom sediments. This study introduces a simple mesocosm method, modeled after previous in situ methods, to measure the germination of plankton resting stage cells. Using this method, seasonal changes in germination fluxes of toxic dinoflagellates resting cysts, specifically Alexandrium fundyense (A. tamarense species complex Group I) and A. pacificum (A. tamarense species complex Group IV), were investigated at a fixed station in Kesennuma Bay, northeast Japan, from April 2014 to April 2015. This investigation was conducted in addition to the typical samplings of seawater and bottom sediments to detect the dinoflagellates vegetative cells and resting cysts. Bloom occurrences of A. fundyense were observed June 2014 and February 2015 with maximum cell densities reaching 3.6 × 10⁶ cells m⁻² and 1.4 × 10⁷ cells m⁻², respectively. The maximum germination fluxes of A. fundyense cysts occurred in April 2014 and December 2014 and were 9.3 × 10³ cells m⁻² day⁻¹ and 1.4 × 10⁴ cells m⁻² day⁻¹, respectively. For A. pacificum, the highest cell density was 7.3 × 10⁷ cells m⁻² during the month of August, and the maximum germination fluxes occurred in July and August, reaching 5.8 × 10² cells m⁻² day⁻¹. Thus, this study revealed the seasonal dynamics of A. fundyense and A. pacificum cyst germination and their bloom occurrences in the water column. Blooms occurred one to two months after peak germination, which strongly suggests that both the formation of the initial population by cyst germination and its continuous growth in the water column most likely contributed to toxic bloom occurrences of A. fundyense and A. pacificum in the bay.     

Allelopathic interactions between the macroalga Hizikia fusiformis (Harvey) and the harmful blooms-forming dinoflagellate Karenia mikimotoi

The effects of algal blooms on seaweeds have been rarely studied, although harmful algal blooms (HABs) are now normally regarded as worldwide incidents. In the present study, the effects of dense Karenia mikimotoi cells on the growth and photosynthesis of Hizikia fusiformis, a common and commercially cultivated macroalga in coastal waters of the East China Sea (ECS), were studied to understand the possible consequences when the mariculture encountered a dense harmful algal bloom. Furthermore, the counteraction of the latter on the growth and photosynthetic activities of K. mikimotoi was determined to evaluate the contribution of H. fusiformis commercial cultivation to environmental improvements. The results showed that the chlorophyll a (Chl a) contents, maximal photochemical efficiency (F_v/F_m) and relative electron transfer rate (rETR) of gas vesicles (specialized leaves), adult and young receptacles of H. fusiformis were all significantly (P < 0.05) inhibited compared with the mono-cultured ones. When compared with mono-cultured H. fusiformis (without K. mikimotoi), the Chl a contents in gas vesicles, adult and young receptacles decreased by 20.6%, 17.6% and 33.2% within 2 weeks. Correspondingly, the F_v/F_m decreased by 7.9%, 37.4% and 43.7%; the apparent photosynthetic efficiency (α) decreased by 9.4%, 47.1% and 48.3%; and rETR decreased by 19.5%, 52.6% and 68.2%, respectively. The Chl a concentration of the mono-cultured K. mikimotoi (without H. fusiformis) increased to 2247.97 μg l⁻¹ from 958.11 μg l⁻¹ within 14 d. Those of the co-cultivated ones (with H. fusiformis), however, increased to 1591.31 μg l⁻¹ on the 8th day and then decreased rapidly to 254.99 (±37.73) μg l⁻¹ after the next 6 days. Furthermore, compared with the mono-cultured K. mikimotoi cells, the F_v/F_m, α and rETR_max of co-cultivated ones decreased by 9.4%, 36.3% and 30.6%, respectively. The results indicated that the mature sporophytes of H. fusiformis were resistant to dense K. mikimotoi blooms and this resistance was organ-dependent as: gas vesicle > adult receptacles > young receptacles. On the other hand, commercial mariculture of H. fusiformis demonstrated the potential of preventing the occurrence of algal blooms.     

Cryptic diversity within the harmful dinoflagellate Akashiwo sanguinea in coastal Chinese waters is related to differentiated ecological niches

Blooms of the harmful dinoflagellate Akashiwo sanguinea are responsible for the mass mortality of fish and invertebrates in coastal waters. This cosmopolitan species includes several genetically differentiated clades. Four clonal cultures were established by isolating single cells from Xiamen Harbour (the East China Sea) for morphological and genetic analyses. The cultures displayed identical morphology but were genetically different, thus revealing presence of cryptic diversity in the study area. New details of the apical structure complex of Akashiwo sanguinea were also found. To investigate whether the observed cryptic diversity was related to environmental differentiation, 634 cells were obtained from seasonal water samples collected from 2008 to 2012. These cells were sequenced by single-cell PCR. For comparison with Chinese material, additional large subunit ribosomal DNA sequences were obtained for three established strains from Malaysian and French waters. To examine potential ecological differentiation of the distinct genotypes, growth responses of the studied strains were tested under laboratory conditions at temperatures of 12 °C to 33 °C. These experiments showed four distinct ribotypes of A. sanguinea globally, with the ribotypes A and B co-occuring in Xiamen Harbour. Ribotype A of A. sanguinea was present year-round in Xiamen Harbour, but it only bloomed in the winter and spring, thus corresponding to the winter type. In contrast, A. sanguinea ribotype B bloomed only in the summer, corresponding to the summer type. This differentiation supports the temperature optimum conditions that were established for these two ribotypes in the laboratory. Ribotype A grew better at lower temperatures compared to ribotype B which preferred higher temperatures. These findings support the idea that various ribotypes of A. sanguinea correspond to distinct ecotypes and allopatric speciation occurred in different climatic regions followed by dispersal.     

Growth and bioactive secondary metabolites of arctic Protoceratium reticulatum (Dinophyceae)

Harmful algal blooms are mainly caused by marine dinoflagellates and are known to produce potent toxins that may affect the ecosystem, human activities and health. Such events have increased in frequency and intensity worldwide in the past decades. Numerous processes involved in Global Change are amplified in the Arctic, but little is known about species specific responses of arctic dinoflagellates. The aim of this work was to perform an exhaustive morphological, phylogenetical and toxinological characterization of Greenland Protoceratium reticulatum and, in addition, to test the effect of temperature on growth and production of bioactive secondary metabolites. Seven clonal isolates, the first isolates of P. reticulatum available from arctic waters, were phylogenetically characterized by analysis of the LSU rDNA. Six isolates were further characterized morphologically and were shown to produce both yessotoxins (YTX) and lytic compounds, representing the first report of allelochemical activity in P. reticulatum. As shown for one of the isolates, growth was strongly affected by temperature with a maximum growth rate at 15 °C, a significant but slow growth at 1 °C, and cell death at 25 °C, suggesting an adaptation of P. reticulatum to temperate waters. Temperature had no major effect on total YTX cell quota or lytic activity but both were affected by the growth phase with a significant increase at stationary phase. A comparison of six isolates at a fixed temperature of 10 °C showed high intraspecific variability for all three physiological parameters tested. Growth rate varied from 0.06 to 0.19 d⁻¹, and total YTX concentration ranged from 0.3 to 15.0 pg  YTX cell⁻¹ and from 0.5 to 31.0 pg YTX cell⁻¹ at exponential and stationary phase, respectively. All six isolates performed lytic activity; however, for two isolates lytic activity was only detectable at higher cell densities in stationary phase.