The toxic benthic dinoflagellates of the genus Ostreopsis in temperate areas: a review

The genus Ostreopsis includes species largely distributed from tropical to temperate marine areas worldwide. Among the nine species of the genus, O. siamensis, O. mascarenensis, O. lenticularis and O. cf. ovata can produce toxins of the palytoxin group. In the last decade Ostreopsis cf. ovata and O. cf. siamensis originated intense blooms in all the rocky Mediterranean Sea coastal areas, typically during summer-late summer. The correct identification of Ostreopsis species in field samples is often problematic as Ostreopsis species are morphologically plastic and hardly discriminable under light microscopy and, therefore, molecular analyses are required. Ostreopsis blooms are often associated with noxious effects on health of both humans and benthic marine organisms mainly carried by aerosol and direct contact with seawater. Environmental factors have been shown to affect toxin content of Ostreopsis which generally produces more toxins per cell when growing under suboptimal conditions. O. cf. ovata is able to produce both temporary and resting cysts. In particular, the resting cysts are able to germinate in laboratory conditions for as long as 5 months after their formation at 25°C, but not at 21°C; the presence of a temperature threshold affecting cyst germination in the laboratory suggests that temperature represents a key factor for Ostreopsis cf. ovata bloom onset in natural environments as well. Several studies conducted to assess the role of abiotic factors (mainly hydrodynamics, water temperature and nutrients) on the bloom dynamics, revealed that the synergic effects of hydrodynamics, temperature and N:P ratios would lead the Ostreopsis blooms in temperate areas. Ostreopsis abundances showed a significant decrease with depth, likely related to light availability, although there are conflicting data about the relationship between light intensity and Ostreopsis growth in experimental conditions. The relationship between Ostreopsis blooms and salinity is not completely clear, complicated by the influence of high nutrient levels often associated to low salinity waters. Finally, Ostreopsis colonize a variety of substrata, although living substrata seems to allow lower concentration of epibionts than any other substrate, probably due to the production of some allelopathic compounds.</p

Marine phycotoxin levels in shellfish-14 years of data gathered along the Italian coast

Along the Italian coasts, toxins of algal origin in wild and cultivated shellfish have been reported since the 1970s. In this study, we used data gathered by the Veterinary Public Health Institutes (IZS) and the Italian Environmental Health Protection Agencies (ARPA) from 2006 to 2019 to investigate toxicity events along the Italian coasts and relate them to the distribution of potentially toxic species. Among the detected toxins (OA and analogs, YTXs, PTXs, STXs, DAs, AZAs), OA and YTX were those most frequently reported. Levels exceeding regulatory limits in the case of OA (≤2,448 μg equivalent kg-1) were associated with high abundances of Dinophysis spp., and in the case of YTXs (≤22 mg equivalent kg-1) with blooms of Gonyaulax spinifera, Lingulodinium polyedra, and Protoceratium reticulatum. Seasonal blooms of Pseudo-nitzschia spp. occur all along the Italian coast, but DA has only occasionally been detected in shellfish at concentrations always below the regulatory limit (≤18 mg kg-1). Alexandrium spp. were recorded in several areas, although STXs (≤13,782 μg equivalent kg-1) rarely and only in few sites exceeded the regulatory limit in shellfish. Azadinium spp. have been sporadically recorded, and AZAs have been sometimes detected but always in low concentrations (≤7 μg equivalent kg-1). Among the emerging toxins, PLTX-like toxins (≤971 μg kg-1 OVTX-a) have often been detected mainly in wild mussels and sea urchins from rocky shores due to the presence of Ostreopsis cf. ovata. Overall, Italian coastal waters harbour a high number of potentially toxic species, with a few HAB hotspots mainly related to DSP toxins. Nevertheless, rare cases of intoxications have occurred so far, reflecting the whole Mediterranean Sea conditions

New Approach Using the Real-Time PCR Method for Estimation of the Toxic Marine Dinoflagellate Ostreopsis cf. ovata in Marine Environment

Background: We describe the development and validation of a new quantitative real time PCR (qrt-PCR) method for the enumeration of the toxic benthic dinoflagellate Ostreopsis cf. ovata in marine environment. The benthic Ostreopsis sp. has a world-wide distribution and is associated during high biomass proliferation with the production of potent palytoxin-like compounds affecting human health and environment. Species-specific identification, which is relevant for the complex of different toxins production, by traditional methods of microscopy is difficult due to the high morphological variability, and thus different morphotypes can be easily misinterpreted. Methodology/Findings: The method is based on the SYBR I Green real-time PCR technology and combines the use of a plasmid standard curve with a ‘‘gold standard’’ created with pooled crude extracts from environmental samples collected during a bloom event of Ostreopsis cf. ovata in the Mediterranean Sea. Based on their similar PCR efficiencies (95% and 98%, respectively), the exact rDNA copy number per cell was obtained in cultured and environmental samples. Cell lysates were used as the templates to obtain total recovery of DNA. The analytical sensitivity of the PCR was set at two rDNA copy number and 8.061024 cell per reaction for plasmid and gold standards, respectively; the sensitivity of the assay was of cells g21 fw or 121 in macrophyte and seawater samples, respectively. The reproducibility was determined on the total linear quantification range of both curves confirming the accuracy of the technical set-up in the complete ranges of quantification over time. Conclusions/Significance: We developed a qrt-PCR assay specific, robust and high sample throughput for the absolute quantification of the toxic dinoflagellate Ostreopsis cf. ovata in the environmental samples. This molecular approach may be considered alternative to traditional microscopy and applied for the monitoring of benthic toxic microalgal species in the marine ecosystems

The toxic benthic dinoflagellates of the genus Ostreopsis in temperate areas: a review

The genus Ostreopsis includes species largely distributed from tropical to temperate marine areas worldwide. Among the nine species of the genus, O. siamensis, O. mascarenensis, O. lenticularis and O. cf. ovata can produce toxins of the palytoxin group. In the last decade Ostreopsis cf. ovata and O. cf. siamensis originated intense blooms in all the rocky Mediterranean Sea coastal areas, typically during summer-late summer. The correct identification of Ostreopsis species in field samples is often problematic as Ostreopsis species are morphologically plastic and hardly discriminable under light microscopy and, therefore, molecular analyses are required. Ostreopsis blooms are often associated with noxious effects on health of both humans and benthic marine organisms mainly carried by aerosol and direct contact with seawater. Environmental factors have been shown to affect toxin content of Ostreopsis which generally produces more toxins per cell when growing under suboptimal conditions. O. cf. ovata is able to produce both temporary and resting cysts. In particular, the resting cysts are able to germinate in laboratory conditions for as long as 5 months after their formation at 25°C, but not at 21°C; the presence of a temperature threshold affecting cyst germination in the laboratory suggests that temperature represents a key factor for Ostreopsis cf. ovata bloom onset in natural environments as well. Several studies conducted to assess the role of abiotic factors (mainly hydrodynamics, water temperature and nutrients) on the bloom dynamics, revealed that the synergic effects of hydrodynamics, temperature and N:P ratios would lead the Ostreopsis blooms in temperate areas. Ostreopsis abundances showed a significant decrease with depth, likely related to light availability, although there are conflicting data about the relationship between light intensity and Ostreopsis growth in experimental conditions. The relationship between Ostreopsis blooms and salinity is not completely clear, complicated by the influence of high nutrient levels often associated to low salinity waters. Finally, Ostreopsis colonize a variety of substrata, although living substrata seems to allow lower concentration of epibionts than any other substrate, probably due to the production of some allelopathic compounds.</p

Karlodinium veneficum feeding responses and effects on larvae of the eastern oyster Crassostrea virginica under variable nitrogen:phosphorus stoichiometry

Mixotrophic feeding can be promoted by nutrient-enriched prey, a nutritional strategy which can provide benefits to some toxic microalgae under nutrient-imbalanced conditions. However, it is unclear how the nutritional condition of the predator or the prey affects the mixotrophy and toxicity of toxin-producing mixotrophs. Laboratory experiments were conducted to measure growth and feeding rates of Karlodinium veneficum with addition of Rhodomonas salina as prey under varied nitrogen (N):phosphorus (P) stoichiometry (molar N:P of 4, 16 and 32) of both predator and prey and with K. veneficum initially in different growth phases (exponential and stationary). Growth rates of initially exponential- and stationary-phase K. veneficum were enhanced in the presence of prey with reciprocal nutrient conditions. Feeding rates (measured as prey death rates) were highest for low-NP K. veneficum initially growing exponentially and mixed with N-rich prey. Maximum feeding rates of low-NP K. veneficum on N-rich prey during exponential growth were ~4-fold higher than the rates of high-NP K. veneficum on N-rich prey. The nutritionally different K. veneficum were tested with larvae of the eastern oyster Crassostrea virginica to compare putative toxicity. Larval mortality was significantly increased in 2 d exposures to high-NP K. veneficum monocultures in both growth phases. When mixed with N-rich prey, the presence of K. veneficum resulted in significantly enhanced larval mortality, but this was not the case for low-NP K. veneficum in exponential phase. Enhanced growth of K. veneficum and increased negative effects of K. veneficum on larval survival appeared to be highest when fed prey with higher N:P content

The use of organic phosphorus by Ostreopsis cf. ovata: a mixotrophic strategy to account for its success?

Many coastal environments are suffering increasing levels of organic nutrients deriving from anthopogenic and microbial activities and this will affect the natural communities of these environments. In addition, the importance of phosphorus as a nutrient that is limiting primary productivity in these areas is also coming to light. Likewise, in recent years, incidences involving Ostreopsis ovata blooms in temperate coastal zones have been reported with increasing frequency, intensity and distribution. So it was decided to investigate a potential link between these actualities. Studies of O. ovata ‘success’ have covered many aspects of its ecology, however, to date there has been no information given about its possible use of organic substrates as nutrient source. Yet there are many reports in the literature on diverse algal groups that can maintain ‘normal’ activity by making use of organic substrates. In this preliminary study, the phosphatase assay was used as convenient and rapid method to assess possible organic nutrition. Phosphatases are a group of enzymes that hydrolyse simple organic compounds and release inorganic phosphate. Evidence has shown that the bulk of enzyme activity is associated with the cell wall or its immediate surroundings, leading to the release of inorganic phosphate external to the cytoplasmic membrane and the subsequent uptake of much of this into the cell. Here we report on the phosphatase activities of O. ovata cultured in media containing inorganic or organic phosphate and natural samples. Primarily the results show that O. ovata could utilise organic P compounds as growth continued unimpeded in organic P only media and the occurrence of high surface phosphatase activity associated with the cells. The results also highlight what seems to be a high constitutive phosphatase activity. This signifies that even when experiencing high ambient nutrient levels, that rates of activity can continue to supply ‘luxury’ levels of P to the cells. It is likely that O. ovata would thrive under high nutrient conditions and have a competitive edge over other groups of organisms that may have product repressible phosphatases

Morphometric analysis of Ostreopsis cf. ovata cells in relation to environmental conditions and bloom phases

Blooms of the toxic benthic dinoflagellate Ostreopsis cf. ovata are associated with noxious effects on human health and mortality of benthic organisms, due to the production of palytoxin-like compounds. We investigated the O. cf. ovata bloom along the Conero Riviera (northern Adriatic Sea) during summer 2009 and 2010, in order to analyse morphometric characteristics in relation to bloom phases and environmental conditions. Up to 1000 cells were measured in each study year in natural samples. The morphometric analysis showed a marked variability in cell size (DV: 18.75-75μm; W: 12.5-60μm), and a relationship between cell dimensions and bloom phases was shown: cells in the final phase had a significantly longer DV than those in both the initial and in the proliferation phases. O. cf. ovata showed significantly lower DV in sheltered sites compared with exposed ones, suggesting that the former represent favourable sites for intense O. cf. ovata proliferation and that turbulence can affect O. cf. ovata growth rate and consequently its cell size. The dimensions of Ostreopsis cells in the water column were significantly higher than those of epiphytic ones, suggesting that resuspended cells in the water column probably derived from a mature benthic population. O. cf. ovata developed from August to November, with the highest abundances on 9th September in 2009 (1.3×10 6cellsg -1 fw, corresponding to 1.6×10 7cellsg -1 dw and 63.8×10 3cellscm -2) and on 19th August in 2010 (1.2×10 6cellsg -1 fw corresponding to 1.6×10 7cellsg -1 dw and 47.8×10 3cellscm -2). The abundances of O. cf. ovata were significantly higher in sheltered than in exposed sites, but such differences were significant only during the proliferation phase, suggesting that hydrodynamics affect abundances mainly during the proliferation bloom phase when the highest abundances are reached

The role of hydrozoans in European sea bass (Dicentrachus labrax) gill disorders in Mediterranean aquaculture

5th International Jellyfish Bloom Symposium, 30 May to 3 June 2016, Barcelona.-- 1 pageFinfish marine aquaculture farms across European coasts have been repeatedly affected by mortality events following the occurrence of episodic high densities of gelatinous cnidarians. Due to their stinging cells and venoms, these jellyfish species may severely damage fish gills. Gill disorders were observed in sea bass (Dicentrarchus labrax) fish farms along the Spanish Mediterranean coast. To investigate the potential for cnidarian-related pathologies affecting cage-reared fish, biweekly monitoring of zooplankton, phytoplankton and farmed fish gills were performed at two aquaculture facilities from south-western Spain from January 2012 to June 2014 (Almería facility) and June 2013 to June 2014 (Málaga facility). Analyzed data showed significant and positive correlation between the densities of planktonic hydrozoans and the recorded fish mortalities; in particular, the most related species were the siphonophores Muggiaea atlantica, Muggiaea kochi, and the actinulae larvae of Ectopleura larynx hydroid which is usually forming part of cage net biofouling community. Moreover, low temperature, high cnidarians densities and farmed fish mortalities were significantly associated. Finally, gill damage scores were positively correlated with cnidarians densities, while other gelatinous zooplankton groups and the studied phytoplankton species seemed not to be related with recorded fish gill disorders and mortality, even if high density peak of Chaetoceros sp. was observed coinciding with fish mortality event in Almería fish farm. This work may provide baseline information to develop methodological action plans and protocols to prevent and mitigate the impacts of jellyfish proliferations on finfish aquaculture farmsPeer Reviewe