Outbreaks Of Paralytic Shellfish Poisoning Research Articles

NUCLEAR FEATURES AND EFFECT OF NUTRIENTS ON GYMNODINIUM CATENATUM (DINOPHYCEAE) SEXUAL STAGES1

Gymnodinium catenatum Graham is an unarmored, cyst‐forming dinoflagellate species responsible for outbreaks of paralytic shellfish poisoning. The nuclear development of the cells during the sexual cycle and the effect of different nitrate and phosphate external levels on sexual stages were studied. Nuclear fusion of gametes occurred before or at the same time as cytoplasmic fusion. During this process, either both nuclei migrated to a central area in the sulcal region, or only one of them migrated to the other nucleus. The motile and longitudinally biflagellated zygote presented a large, pear‐shaped nucleus, and either divided or encysted. Planozygotes and germlings underwent similar division processes, which suggested an uncoordinated meiosis in both encysting and non‐encysting zygotes. Encystment in culture was greater under low nitrate and phosphate limitation (L/15) than when only one or neither of these nutrients were added (L‐N, L‐P, and ‐N‐P). However, planozygotes individually monitored achieved the maximum encystment (40%) in a medium with no phosphate or nitrate added (‐N‐P), while most of them divided (70%–90%) in replete (L1) or half‐replete (L‐N and L‐P) media. Low levels of nitrate in the medium of cyst formation promoted a deficient development of the cyst wall. On the other hand, low phosphate levels in the medium of germination prevented both planozygote and germling division and lowered the final germination frequencies of cysts. The minimum dormancy, with an average value of 13.7±5.5 days, was not affected by any of the nutritional conditions studied.

Infecciones por Vibrio parahaemolyticus e intoxicaciones por algas: problemas emergentes de salud pública en Chile

There is interest in the paradigm that relates environmental sea changes to the emergence of diseases that affect both aquatic organisms in the sea and human beings. The emergence of Vibrio parahaemolyticus as an important cause of epidemic summer diarrhea in 2004 and 2005, confined mainly to the tenth region in Chile, could be a manifestation of this trend. This and other areas of the country have also experienced several outbreaks of paralytic shellfish poisoning (PSP), diarrheal shellfish poisoning (DSP) and amnesic shellfish poisoning (ASP) caused by harmful algal blooms (HAB) of Alexandrium catenella, Dinophysis acuta and Pseudonitzchia species, respectively. The short historical record of these pathological phenomena in Chile suggests that they are increasing in frequency and expanding their geographical range. The V parahaemolyticus isolates responsible for the Chilean outbreaks correspond mainly to the pandemic strain O3:K6. HAB found in Chile and the intoxications caused by them have similar biological characteristics to those described in other areas of the world. The tenth region, the area where these problems are emerging, produces approximately 80-90% of the shellfish consumed in Chile and a large proportion of the shellfish that is exported. Prevention of these public health problems can be attained by developing policies that increase environmental surveillance for Vibrios and toxic algae, improve the epidemiological surveillance of acute diarrhea and algal intoxications after the ingestion of raw bivalves, and educate the population on the mode of transmission of these diseases. Scientific capacity and laboratories need to be developed to widen the limited knowledge of the biology of Vibrio and toxic algae and the environmental factors that favor their emergence as public health and economic problems in Chile.

Identification and Characterization of Potentially Algal‐lytic Marine Bacteria Strongly Associated with the Toxic Dinoflagellate Alexandrium catenella

The toxic dinoflagellate Alexandrium catenella isolated from fjords in Southern Chile produces several analogues of saxitoxin and has been associated with outbreaks of paralytic shellfish poisoning. Three bacterial strains, which remained in close association with this dinoflagellate in culture, were isolated by inoculating the dinoflagellate onto marine agar. The phenotypically different cultivable bacterial colonies were purified. Their genetic identification was done by polymerase chain reaction amplification of the 16S rRNA genes. Partial sequence analysis suggested that the most probable affiliations were to two bacterial phyla: Proteobacteria and the Cytophaga group. The molecular identification was complemented by morphological data and biochemical profiling. The three bacterial species, when grown separately from phytoplankton cells in high-nutrient media, released algal-lytic compounds together with aminopeptidase, lipase, glucosaminidase, and alkaline phosphatase. When the same bacteria, free of organic nutrients, were added back to the algal culture they displayed no detrimental effects on the dinoflagellate cells and recovered their symbiotic characteristics. This observation is consistent with phylogenetic analysis that reveals that these bacteria correspond to species distinct from other bacterial strains previously classified as algicidal bacteria. Thus, bacterial-derived lytic activities are expressed only in the presence of high-nutrient culture media and it is likely that in situ environmental conditions may modulate their expression.

Toxic Alexandrium blooms in the western Gulf of Maine: The plume advection hypothesis revisited

The plume advection hypothesis links blooms of the toxic dinoflagellate Alexandrium fundyensein the western Gulf of Maine (GOM) to a buoyant plume derived from river outflows. This hypothesis was examined with cruise and moored-instrument observations in 1993 when levels of paralytic shellfish poisoning (PSP) toxins were high, and in 1994 when toxicity was low. A coupled physical‐biological model simulated hydrography and A. fundyense distributions. Initial A. fundyense populations were restricted to low-salinity nearshore waters near Casco Bay, but also occurred in higher salinity waters along the plume boundary. This suggests two sources of cells—those from shallow-water cyst populations and those transported to shore from offshore blooms in the eastern segment of the Maine coastal current (EMCC). Observations confirm the role of the plume inA. fundyense transport and growth. Downwelling-favorable winds in 1993 transported the plume and its cells rapidly alongshore, enhancing toxicity and propagating PSP to the south. In 1994, sustained upwelling moved the plume offshore, resulting in low toxicity in intertidal shellfish. A. fundyense blooms were likely nutrient limited, leading to low growth rates and moderate cell abundances. These observations and mechanisms were reproduced by coupled physical‐biological model simulations. The plume advection hypothesis provides a viable explanation for outbreaks of PSP in the western GOM, but should be refined to include two sources for cells that populate the plume and two major pathways for transport: one within the low-salinity plume and another where A. fundyense cells originating in the EMCC are transported along the outer boundary of the plume front with the western segment of the Maine coastal current.

Dinoflagellate cysts in recent marine sediments from Scapa Flow, Orkney, Scotland

To determine the composition, abundance and horizontal distribution of resting cysts in modern coastal sediments from Scapa Flow, Orkney, Scotland, sediment samples were collected from 12 stations. Twenty-six dinoflagellate cyst types representing eight motile-defined genera and one cyst-defined genus were observed. Four species or species groups dominated the assemblage for the Flow as a whole, Scrippsiella trochoidea, unidentified round brown cysts, Polykrikos schwartzii and Alexandrium tamarense. Total cyst abundance ranged from 37–1524 cysts ml−1 wet sediment. The majority of cysts occurred in the central area of the Flow, where higher densities were observed. Of particular importance is the distribution and abundance of cysts of A. tamarense. Since 1991 there have been annual toxic episodes of paralytic shellfish poisoning, caused by the vegetative stage of A. tamarense, in Scapa Flow, leading to widespread bans on all shellfish activities for months at a time. Cysts of A. tamarense were widely distributed within the Flow and ranged from 0–212 cysts ml−1 wet sediment. The overall widespread distribution and higher abundances of cysts of A. tamarense in the central areas of the Flow indicate potential seedbeds for initiation of future vegetative growth and subsequent outbreaks of paralytic shellfish poisoning.

Offshore blooms of the red tide dinoflagellate, Alexandrium sp., in the Gulf of Maine

Paralytic shellfish poisoning (PSP) occurs nearly every year in the Gulf of Maine. In a study of dynamics of the causative organism, the toxic dinoflagellate Alexandrium sp., we conducted three surveys of the coastal and offshore waters of Gulf of Maine during the summer of 1998, sampling more than 200 stations during each cruise in June, July and August. Hydrographic data were collected and concentrations of phytoplankton chlorophyll, inorganic nutrients and densities of Alexandrium cells were measured in discrete water samples. The distributions of Alexandrium at the surface and in subsurface waters displayed maximum cell densities in the offshore waters of the Gulf on all three cruises. Highest cell densities in surface waters (ca. 5.5×10 3 cells l −1) were observed in two broad patches: one in the Bay of Fundy and another in shelf and offshore waters of the central and eastern Gulf of Maine in association with the Eastern Maine Coastal Current. Highest subsurface densities of cells appeared to be associated with the frontal edges beyond the cold surface waters associated with the Eastern Maine Coastal Current. As the summer progressed, the highest surface densities of Alexandrium receded toward the eastern portions of the Gulf and the Bay of Fundy. We suggest that the offshore distributions of relatively high densities of Alexandrium are naturally occurring and can be related to inorganic nutrient fluxes, and to the ambient light field as it varies seasonally and vertically. Locations of high cell densities were described and interpreted using a nondimensional light-nutrient parameter, computed as the ratio of the depth of the 10% surface irradiance to the depth of 4 μM NO 3 concentration. Possible mechanisms responsible for periodic development of PSP outbreaks in nearshore shellfish beds are discussed.

Paralytic Shellfish Poisoning on the East Coast of the UK in Relation to Seasonal Density-driven Circulation

Paralytic shellfish poisoning (PSP) toxin associated with the dinoflagellate Alexandrium tamarense is found on the north-east coast of the UK in late spring/early summer. Severe outbreaks are sporadic, and knowledge of the cause and origin of the phytoplankton blooms and whether they develop from a diffuse source or from a seed population is uncertain. Recent observations of the circulation of the region demonstrate a persistent southward near-coastal flow associated with strong bottom fronts bounding a pool of cold dense bottom water isolated below the seasonal (spring/summer) thermocline. Flows extend continuously for ~500 km from the Firth of Forth to Flamborough Head before passing offshore to the Dogger Bank. These observations suggest that dinoflagellates originating from the high concentrations of A. tamarense cysts in the sediment of the Firth of Forth act to maintain a dinoflagellate population in the coastal region south to Flamborough Head, thereby maintaining the risk of PSP outbreaks.

Bloom dynamics of toxic Alexandrium species in the northeastern U.S

Coastal waters of the northeastern U.S. are subject to recurrent outbreaks of paralytic shellfish poisoning (PSP) caused by toxic dinoflagellates in the genus Alexandrium. PSP is not uniform across the large region, but instead reflects Alexandrium growth and toxin accumulation in five separate habitats or zones defined by circulation patterns and the discontinuous distribution of the dinoflagellates. Each of these habitats has a unique set of environmental and oceanographic forcings that determine the timing and extent of bloom development and transport and that regulate the extent of genetic exchange with adjacent populations. Several habitats (e.g. the southwestern Gulf of Maine, Massachusetts Bay, and Georges Bank) are linked hydrographically and may share the same Alexandrium population via large‐scale transport in a. coastal current, whereas the other two habitats (eastern Maine and southern salt ponds‐embayments) seem to be isolated and have little or no hydrographic or genetic linkage to adjacent regions during bloom seasons. My paper provides an overview of the regional ecology and oceanography of Alexandrium through a focus on these five subpopulations. Issues that relate to PSP and Alexandrium dynamics throughout the world are highlighted, including species dispersal, the role of cysts and “initiation zones” in bloom development, and the influence of large‐ and small‐scale hydrography on population development and transport. The ability of Alexandrium to colonize multiple habitats and to persist over a large region is emphasized in recognition of the adaptability and resilience of this important organism.

Interannual variability of PSP outbreaks on the north east UK coast

Paralytic shellfish poisoning (PSP) occurs sporadically on the NB UK coast. The degree of toxicity shows considerable interannual variability, but particularly severe events occurred in 1968 and 1990. The time sequence of PSP toxin production in 1990 is described and compared with 1989 when no significant PSP toxin occurred. In 1990, PSP toxin was widespread in shellfish samples taken on 300 km of coastline, from Berwick to Whitby, and toxin was present at high concentrations for >1 month. The distribution of Alerandrium tamarense cysts in the sediments is described. High concentrations were found in the Firth of Forth and also in a number of regions offshore of the Scottish and English coasts. A water transport model has been used to estimate back trajectories, with the aim of determining the source of the A.tamarense bloom. The Firth of Forth has previously been suggested as the seed bed for A.tamarense outbreaks in the area, but the transport model clearly shows that A.tanwrense moved inshore over a wide area in 1990; there was no single source of the bloom. Sea surface temperatures, estimated from satellite imagery, show that water temperatures were much higher at the end of April 1990, when the bloom occurred, than in 1989 when PSP toxin incidence was very low. These conditions would have resulted in early seasonal stratification and would have favoured phytoplankton growth in the water column.

The effects of temperature, growth medium and darkness on excystment and growth of the toxic dinoflagellate Gymnodinium catenatum from northwest Spain

The chain-forming dinoflagellate Gynmodinium catenatum Graham causes recurrent outbreaks of paralytic shellfish poisoning (PSP) in the Galician Rias Bajas (northwest Spain). A sediment survey in Ria de Vigo in April 1986 indicated that the highest concentrations of cysts of this species were located in the middle sections of the ria, with maximum abundance of 310 cysts cm−3. The effects of temperature, growth medium composition and irradiance on the germination of laboratory-produced resting cysts were investigated. Newly formed cysts required very little time for maturation, as excystment was possible within 2 weeks of encystment. Growth media did not affect germination success. In contrast, the excystment rate was retarded signifiantly in darkness. Germination was also strongly affected by temperature, with ˜75% excystment success at 22–28°C and little or no germination below 11°C after 1 month of incubation. In culture, the optimum growth rate of vegetative cells was between 22 and 28°C, the highest rate being 0.53 divisions day−1 at 24°C. Growth did not occur at temperatures < 11°C or >30°C. These results are important with respect to the different hypotheses proposed to explain the initiation of G.catenatum blooms in the Galician Rias Bajas and Northern Portugal. The pattern of G.catenatum bloom development along this coast has been related to seasonal upwelling in the area, with major blooms occurring during the autumn as warmer offshore surface water is transported towards the coast when upwelling relaxes. The landward transport of established offshore populations of G.catenatum with the warm surface layer remains a viable explanation for the observed blooms within the rias, but alternatively, our data suggest that cysts within the rias can provide the inoculum population at times conducive to growth and bloom formation. Even though newly formed G.catenatum cysts have a very short maturation time and can germinate in darkness across a wide temperature range, bloom development will be significant only during the late summer and early autumn, since in other months light levels at the sediment surface and temperatures throughout the water column are too low for significant germination or growth.

Paralytic shellfish poisoning in northwest Spain: The toxicity of the dinoflagellate Gymnodinium catenatum

D. M. Anderson, J. J. Sullivan and B. Reguera. Paralytic shellfish poisoning in northwest Spain: the toxicity of the dinoflagellate Gymnodinium catenatum. Toxicon 27, 665–674, 1989.—The highly productive mussel fishery in the Rias Bajas region of northwest Spain has experienced several outbreaks of paralytic shellfish poisoning (PSP) beginning in 1976. In this study, similarities in the HPLC analyses of extracts from toxic shellfish, plankton tows and cultured dinoflagellates from the Rias Vigo and Pontevedra clearly indicate that Gymnodinium catenatum Graham is the organism responsible for recent PSP episodes. The toxin profile of the dinoflagellate contains an unusually high proportion of the low potency sulfocarbamoyl toxins ( ca. 90–95 mole %), although a major portion of the overall toxicity is due to the more potent saxitoxin that is present at 5–10% of the total. Toxin profiles of shellfish showed approximately the same composition as that of the dinoflagellate, although the shellfish contained several carbamate toxins (GTX I, GTX II, GTX IV and NEO) that were not detected in G. catenatum culture extracts. The shellfish also contained decarbamoyl toxins (dc-GTX II and dc-GTX-III) at approximately 2% of the total profile. Since these were not detected in the dinoflagellate, their presence reflects either chemical or enzymatic conversion within the shellfish.

Influence of upwelling relaxation on dinoflagellates and shellfish toxicity in Ria de Vigo, Spain

Outbreaks of paralytic shellfish poisoning (PSP) along the north-west coast of Spain have become a serious threat to the extensive mussel farming industry in that region over the last decade. During the summer, high phytoplankton productivity is supported by the sustained upwelling of nutrient-rich deep water into the rias. An episode of PSP in the autumn of 1985 in Ria de Vigo coincided with the sudden appearance, rapid numerical increase, and dominance of two chain-forming dinoflagellates, Gymnodinium catenatum and Protogonyaulax affinis. Field data suggest that warm offshore surface water was transported into the ria as the summer upwelling ceased. This occurred when winds changed from northerly (upwelling favourable) to southerly or westerly (upwelling unfavourable); the injected water contained established populations of oceanic and neritic dinoflagellates. The simultaneous appearance and dominance of two dinoflagellates that form long chains leads us to speculate that the small-scale downwelling of water within the ria favoured efficient swimmers among the phytoplankton. These data not only implicate these two species as possible sources of the PSP toxins in local mussels, but they also suggest the feasibility of developing a bloom prediction capability for some dinoflagellate species based in part on an upwelling index that can indicate when offshore surface waters might be forced into the rias.

An endogenous annual clock in the toxic marine dinoflagellate Gonyaulax tamarensis.

Blooms of the toxic dinoflagellate Gonyaulax tamarensis (synonyms Protogonyaulax tamarensis and Alexandrium tamarense) cause outbreaks of paralytic shellfish poisoning (PSP) in coastal waters throughout the world. In the Gulf of Maine, episodes occur between April and November, a seasonality due in part to life-cycle alternations between motile, vegetative cells and resting cysts which overwinter in bottom sediments. Newly formed cysts have a mandatory 2-6 month dormancy period during which germination is not possible, but once mature, the resting state will continue if temperatures are unfavourable or oxygen is unavailable. We now report another factor controlling germination of cysts of G. tamarensis from deep coastal waters--an endogenous annual clock that can override an otherwise favourable environment for germination. Similar annual variability in germination has not been observed for cysts of this species from shallow estuaries. These results represent the first conclusive demonstration of an endogenous circannual rhythm in a marine plant. They are evolutionarily and ecologically significant because an endogenous annual clock can lead to the release of motile cells into deep and relatively invariant bottom waters at those times when temperature and light at the surface are suitable for growth. In shallow waters where seasonal variability is large and extends to bottom sediments, a strategy similar to that of the seeds of terrestrial plants would be more appropriate, namely a direct coupling between germination and the external environment.

International Conference on “Red Tide”

Outbreaks of paralytic shellfish poisoning, known as ‘red tide,’ annually cause several billion dollars' worth of damage around the world.To explore current knowledge about these little‐understood but economically important algal blooms, the Massachusetts Science and Technology Foundation is planning and coordinating an international conference on the nature, occurrence, causes, effects, possible prediction, and prevention of red tide.