INTRA‐CELLULAR AND EXTRA‐CELLULAR TOXINS IN THE RED TIDE DINOFLAGELLATE,GYMNODINIUM BREVE

The marine dinoflagellate, Gymnodinium breve (Davis), produces several neurotoxins that cause neurotoxic shellfish poisoning (nsp), massive fish kills and respiratory irritation in marine mammals and humans. The common method for discerning toxic levels of G. breve for public health advisories is enumeration of live cells in a given water mass. In this study, laboratory cultures, as well as natural blooms, were added to a stirred ultra‐filtration cell concentrator to separate viable cells containing intra‐cell toxins from ambient water containing extra‐cell toxins. Methods were validated using various mixtures of lysed and whole G. breve laboratory culture. Extractions and recovery of brevetoxins were done using a C‐18 bonded‐phase glass fiber extraction disc eluted with methanol. Total PbTx toxin concentrations were quantified by HPLC/UV using a C‐18 column and an 85:15 methanol:water (1 ml min^?1) isocratic elution at 215 nm. This method of separation and extraction was subsequently applied to water samples collected during natural blooms along two different areas of the Florida Gulf coast. The results indicated that early stages of G. breve blooms contained primarily intra‐cell toxins with extra‐cell toxins increasing as the bloom progressed, even though very few viable G. breve cells were present. This suggests that enumeration of cells alone may be insufficient and additional toxin quantitation is necessary.     

NOVEL STEROLS OF THE TOXIC DINOFLAGELLATE KARENIA BREVIS (DINOPHYCEAE): A DEFENSIVE FUNCTION FOR UNUSUAL MARINE STEROLS?1

The “red tide” organism Karenia brevis (Davis) Hansen & Moestrup (=Gymnodinium breve Davis) produces a mixture of brevetoxins, potent neurotoxins responsible for neurotoxic shellfish poisoning in humans and massive fish kills in the Gulf of Mexico and the southern Atlantic coast of the United States. The sterol composition of K. brevis was found to be a mixture of six novel and rare Δ⁸⁽¹⁴⁾ sterols. The two predominant sterols, (24R)‐4α‐methylergosta‐8(14), 22‐dienol and (24R)‐4α‐methyl‐27‐norergosta‐8(14), 22‐dienol, were named gymnodinosterol and brevesterol and represent potentially useful biomarkers for K. brevis. A possible function for such unusual marine sterols is proposed whereby structural modifications render the sterols non‐nutritious to marine invertebrates, reducing predation and thereby enhancing the ability of the dinoflagellates to form massive blooms.     

Anatomy of a red tide bloom off the southwest coast of Florida

A massive outbreak of Karenia brevis that had been ongoing for several months along the southwestern coast of Florida was sampled in early September 2005 off Sanibel Island to assess the utility of bio-optical features and ataxonomic analysis (quantification of eukaryotic and cyanobacterial picoplankton) by flow cytometry in monitoring red tide blooms. Sea-surface sampling followed aircraft visual location of discolored water. Within the most concentrated area of the bloom, chlorophyll a values exceeded 500 μg l⁻¹, and concentrations of nitrate (0.3 μM ± 0.0) and ammonium (<0.2 μM) were depleted compared to high concentrations of total dissolved nitrogen, total dissolved phosphorus, and soluble reactive phosphorus (141 ± 34 μM, 16.5 ± 2.5 μM, and 6.44 ± 0.57 μM, respectively). Low water clarity in the bloom (Secchi depth transparency 0.3 m, K_d estimated at 4.83 m⁻¹) was strongly influenced by attenuation from dinoflagellates as well as chromophoric dissolved organic matter (CDOM). The fact that the K. brevis bloom occurred in lower-salinity (30 psu), high-nutrient waters implicates riverine transport of land-based nutrients as a source of nutrient supplies that fueled or sustained the bloom. Throughout ongoing efforts to advance modeling and technological capabilities that presently lack reliable predictive capability, bio-optical remote sensing via aerial flyovers along with in-water sensor data can continue to provide accurate coverage of relatively large temporal and spatial features. Flow cytometry can provide conservative (because of some cell lysis), rapid, near-real-time validation of bloom components. The concentration and position of the organisms, along with water mass scalars, can also help to diagnose factors promoting K. brevis bloom development and dispersion.     

Study of phytoplankton characteristics in Tolo Harbour,Hong Kong,by HPLC analysis of chemotaxonomic pigments

Spatial and seasonal characteristics of phytoplankton in Tolo Harbour, Hong Kong, were studied by microscopic observation of phytoplankton samples and HPLC analysis of chemotaxonomic pigments. Diatoms dominated the phytoplankton. Common diatoms included Skeletonema costatum and species of Cerataulina, Leptocylindrus, Pseudo-nitzschia and Thalassiosira. Dinoflagellates occurred sporadically and mainly in the inner part of the harbour. The dinoflagellate Scrippsiella trochoidea was the causative organism for the red tide occurrences in March, April and September 2001. Significant positive correlations between fucoxanthin and diatoms and between peridinin and dinoflagellates suggested that fucoxanthin and peridinin were valuable chemotaxonomic markers for diatoms and dinoflagellates, respectively. Analysis of pigment ratios revealed that red tide events caused by dinoflagellates were marked by increase in the value of PERI:chl a and decrease in the value of FUCO:chl a. Increase in the value of FUCO:chl a also revealed the presence of a dense population of Pseudo-nitzschia that was not indicated by increase in chlorophyll a and fucoxanthin concentrations. Pigment analysis also revealed the presence of cyanobacteria, silicoflagellates, cryptophytes and green algae in the surface waters of Tolo Harbour.     

ALGICIDAL BACTERIA ACTIVE AGAINST GYMNODINIUM BREVE (DINOPHYCEAE). I. BACTERIAL ISOLATION AND CHARACTERIZATION OF KILLING ACTIVITY1,3

Interactions between bacteria and species of harmful and/or toxic algae are potentially important factors affecting both the population dynamics and the toxicity of these algae. Recent reports of bacteria lethal to certain harmful algal bloom (HAB) species, coupled with a rapidly evolving interest in attempting to minimize the adverse effects of HABs through various prevention, control, and mitigation strategies, have focused attention on defining the role of algicidal bacteria in bloom termination. The aim of the present study was to determine whether algicidal bacteria active against Gymnodinium breve Davis, a dinoflagellate responsible for frequent and protracted red tides in the Gulf of Mexico, are present in the waters of the west Florida shelf. To date, we have isolated two bacterial strains from this region lethal to G. breve and have begun to characterize the algicidal activity of one of these strains, 41-DBG2. This bacterium, a yellow-pigmented, gram-negative rod, was isolated from waters containing no detectable G. breve cells, suggesting that such bacteria are part of the ambient microbial community and are not restricted to areas of high G. breve abundance. Strain 41-DBG2 produced a dissolved algicidal compound(s) that was released into the growth medium, and the algicide was effective against the four Gulf of Mexico G. breve isolates tested as well as a closely related HAB species that also occurs in this region, Gymnodinium mikimotoi Miyake et Kominami ex Oda. Nonetheless, data showing that a nontoxic isolate of Gymnodinium sanguineum Hirasaka from Florida Bay was not affected indicate that the algicidal activity of this bacterium does exhibit a degree of taxonomic specificity. Our efforts are currently being directed at resolving several critical issues, including the identity of the algicide(s), the mechanisms regulating its production and ability to discriminate between target algal species, and how the growth rate of 41-DBG2 is affected by the presence of G. breve cells. We have also proposed a conceptual model for interactions between algicidal bacteria and their target species to serve as a testable framework for ensuing field studies.     

Severe Karenia brevis red tides influence juvenile bottlenose dolphin (Tursiops truncatus) behavior in Sarasota Bay,Florida

Harmful algal blooms (HABs) are natural stressors in the coastal environment that may be increasing in frequency and severity. This study investigates whether severe red tide blooms, caused by Karenia brevis, affect the behavior of resident coastal bottlenose dolphins in Sarasota Bay, Florida through changes to juvenile dolphin activity budgets, ranging patterns, and social associations. Behavioral observations were conducted on free‐ranging juvenile dolphins during the summer months of 2005–2007, and behavior during red tide blooms was compared to periods of background K. brevis abundance. We also utilized dolphin group sighting data from 2004 to 2007 to obtain comparison information from before the most severe recent red tide of 2005 and incorporate social association information from adults in the study area. We found that coastal dolphins displayed a suite of behavioral changes associated with red tide blooms, including significantly altered activity budgets, increased sociality, and expanded ranging behavior. At present, we do not fully understand the mechanism behind these red tide‐associated behavioral effects, but they are most likely linked to underlying changes in resource availability and distribution. These behavioral changes have implications for more widespread population impacts, including increased susceptibility to disease outbreaks, which may contribute to unusual mortality events during HABs.     

Nitrate metabolism of the red tide dinoflagellate Gonyaulax polyedra Stein

Certain idiosyncracies in the metabolism of nitrogen and diurnal vertical migration may account for the development and persistence of Gonyaulax polyedra Stein red tides along the Southern California Coast.In culture, G. polyedra has the ability for both uptake and assimilation of nitrate in the dark and this together with its enhancement by previous N-starvation could enable these dinoflagellates to meet 50–100 % of their daily nitrogen requirements for growth from dark assimilation alone. Less pronounced light-dark variations in nitrate assimilation and a greater stability of the nitrate assimilatory enzymes, together with the ability to migrate into nitrate-rich subsurface waters at night, probably give G. polyedra and other red tide dinoflagellates a competitive advantage over coastal diatoms during the ‘upwelling season’, when most red tides occur.     

Florida red tide perception: Residents versus tourists

The west coast of Florida has annual blooms of the toxin-producing dinoflagellate, Karenia brevis with Sarasota, FL considered the epicenter for these blooms. Numerous outreach materials, including Frequently Asked Question (FAQ) cards, exhibits for local museums and aquaria, public beach signs, and numerous websites have been developed to disseminate information to the public about this natural hazard. In addition, during intense onshore blooms, a great deal of media attention, primarily via newspaper (print and web) and television, is focused on red tide. However to date, the only measure of effectiveness of these outreach methods has been counts of the number of people exposed to the information, e.g., visits to a website or number of FAQ cards distributed. No formal assessment has been conducted to determine if these materials meet their goal of informing the public about Florida red tide. Also, although local residents have the opinion that they are very knowledgeable about Florida red tide, this has not been verified empirically. This study addressed these issues by creating and administering an evaluation tool for the assessment of public knowledge about Florida red tide. A focus group of Florida red tide outreach developers assisted in the creation of the evaluation tool. The location of the evaluation was the west coast of Florida, in Sarasota County. The objective was to assess the knowledge of the general public about Florida red tide. This assessment identified gaps in public knowledge regarding Florida red tides and also identified what information sources people want to use to obtain information on Florida red tide. The results from this study can be used to develop more effective outreach materials on Florida red tide.     

Winter condition of marine plankton populations in Saanich inlet,B.C., canada. I. Phytoplankton and its surrounding environment

Weekly sampling was carried out in Saanich Inlet, British Columbia throughout the winter of 1975–1976. The surface water column was characterized by exposure to low solar radiation energy (<150 g cal·cm^?2 · day^?1), slight stratification with occasional vertical mixing, and abundant algal nutrients. Phytoplankton were mostly distributed above 5 m in the water column, with a fairly low biomass averaging <1 μgchla·1^?1. Dominant phytoplankton organisms were nanoflagellates occasionally accompanied by dinoflagellates as the second dominant. Centric diatoms, which were dominant in the blooms, were always present but less than a few percentage of the total phytoplankton biomass. Daily photosynthetic productivity was exclusively limited by available radiant energy. Low solar radiation and occasional mixing of the surface zone prohibited the centric diatoms from becoming dominant.     

Why no red tide was observed on the West Florida Continental Shelf in 2010

Over the past two decades, the two most anomalous years for water properties on the west Florida continental shelf were 1998 and 2010. In both instances, the shelf was ventilated by relatively cold, nutrient-rich waters of deep ocean origin, which reset the background state underlying shelf ecology. The ventilation in both of these years derived from prolonged interactions of the Gulf of Mexico Loop Current with the shelf slope near the Dry Tortugas located on the southwest corner of the shelf. By contacting relatively shallow isobaths, the boundary current interactions there set the entire shelf into motion, facilitating upwelling across the shelf break, even to DeSoto Canyon some 500 km away, and then across the shelf to the near shore. Such prolonged and intense upwelling of nutrient-rich water in 2010 contrasted with the more typically occurring locally wind driven upwelling conditions, whereby waters upwelled at the near shore are from the inner shelf, versus the deep ocean. Thus not all upwelling scenarios have similar consequences. Whereas the typical wind driven upwelling scenario is necessary for Karenia brevis red tide blooms to manifest along the coastline, the rarer, deep ocean induced upwelling scenario (as occurred in 1998 and particularly in 2010) acts to suppress K. brevis red tides because of the elevated inorganic nutrient conditions that they facilitate. Hence, minimal cell counts above background were observed in 1998, and no cell counts above background were observed in 2010. We conclude that the lack of red tide along the west coast of Florida in 2010 was due to anomalously large and protracted upwelling of nutrient-rich waters of deep ocean origin caused by Loop Current and eddy interactions with the shelf slope.     

OBSERVATIONS ON THE PECULIAR DIURNAL MIGRATION OF A RED TIDE DINOPHYCEAE IN TROPICAL SHALLOW WATERS1

The dinoflagellate Peridinium cf. quinquecorne Abé forms red tide-like blooms in eutrophic shallow waters in the Philippines. The organism moves into a distinct near-surface layer when intensive solar radiation occurs, but only during the incoming tide. Shortly before high tide, regardless of light levels, the dinoflagellates seem to disappear. Simple experiments show that once intensive radiation has been reduced Peridinium quinquecorne moves out of the water column and attaches itself to solid objects away from the light. The morphology of the organism, especially as related to attachment, was studied through SEM. Its high swimming velocity and the reaction to radiation and tidal changes are described. The possibility that, superimposed on its reaction to light, this dinoflagellate may follow intrinsic tide-dependent oscillations is discussed.     

A spring poleward current and its influence on microplankton assemblages and harmful dinoflagellates on the western Iberian coast

Along-shore currents can propagate harmful algal blooms (HABs) over long distances in many coastal areas of the ocean. Harmful dinoflagellate blooms on the west coast of Iberia frequently occur when the Iberian poleward current (IPC) establishes on the continental slope. This has led to the suggestion that HABs could be transported northward by the IPC. To examine this possibility, the microplankton composition along the west coast of Iberia was studied in May 1993 coinciding with the presence of the IPC. The microplankton of the IPC was almost exclusively composed of small flagellates, with the notable absence of the harmful species usually associated with coastal waters. The primary influence of the IPC was to confine coastal microplankton populations to the shelf, where a downwelling convergence prevented their export from the coastal environment. Microplankton assemblages on the shelf revealed a north–south gradient related to different stages of succession. Earlier stages of succession in which diatoms were prominent were found on the northern shelf, whereas dinoflagellates were more abundant in the south. The toxic species Gymnodinium catenatum, which was only present in the southern shelf, did not show a northward transport associated with the IPC. It is suggested that the northward spreading of HABs along the west coast of Iberia must be related to the interaction between the IPC, which accumulates coastal populations on the shelf, and the latitudinal progress of microplankton succession that determines species composition. Thus, during the course of the season, HABs are likely to be observed in the south prior to their development in the north.     

A modified assay to determine hemolytic toxin variability among Karenia clones isolated from the Gulf of Mexico

Karenia brevis (formerly Gymnodinium breve) is a toxic marine dinoflagellate generally restricted to the Gulf of Mexico and is the main causative organism in fish kills, shellfish intoxications and respiratory distress in humans following bloom events. K. mikimotoi is a morphologically similar co-occurring species which is toxic in other parts of the world oceans, but has not been recognized as a major contributor in toxicity of blooms within the Gulf of Mexico. Recently there has been increasing evidence of the simultaneous production of a variety of bioactive compounds in addition to potent neurotoxins (brevetoxin) in Karenia brevis isolates. These compounds are potentially ichthyotoxic and have been shown to cause hemolysis in several bioassays [Eshbach, E., Scharsack, J., John, U., Medlin, L., 2001. Improved erythrocyte lysis assay in microtitre plates for the sensitive detection and efficient measurement of haemolytic compounds from ichthyotoxic algae. J. Appl. Toxicol. 21, 513–519; Kirkpatrick, B., Fleming, L.E., Squicciarini, D., Backer, L.C., Clark, R., Abraham, W., Benson, J., Cheng, Y.S., Johnson, D., Pierce, R., Zaias, J., Bossart, G.D., Baden, D.G., 2004. Literature review of Florida red tide: implications for human health effects. Harmful Algae 3, 99–115]. Presence of hemolytic compounds may therefore add to the overall toxicity levels of bloom events. Current monitoring methods include assays which are highly sensitive in brevetoxin detection and yet may not target other harmful compounds.By adapting protocols developed by Eshbach et al. [Eshbach, E., Scharsack, J., John, U., Medlin, L., 2001. Improved erythrocyte lysis assay in microtitre plates for the sensitive detection and efficient measurement of haemolytic compounds from ichthyotoxic algae. J. Appl. Toxicol. 21, 513–519], Red drum (Sciaenops ocellatus) erythrocytes were used to create a modified bioassay to detect hemolytic activity of crude algal extracts. Red drum was selected because it is endemic to coastal areas throughout the Gulf of Mexico and is sensitive to Karenia blooms, and thus makes this species a valid ecological target. Preliminary data has shown this method is sensitive for use in assessing hemolysis induced by laboratory cultures down to levels of 1 × 10³ cells mL⁻¹. Results showed an unexpectedly high level of hemolytic activity among K. mikimotoi clones, with one Texas strain inducing significantly higher hemolysis compared to Florida K. brevis isolates. Using this approach, future research efforts will examine the difference in production of hemolytic compounds among various Karenia clones.     

Modeling the influence of nutrients, turbulence and grazing on Pfiesteria population dynamics

A semi-idealized marine ecosystem model, designed as a heuristic tool for exploring the population dynamics of non-inducible versus toxic forms of Pfiesteria is described. The model is based on empirical evidence suggesting that these differing functional types of Pfiesteria also differ substantially in terms of what they eat and how they utilize it to optimize their growth. Non-inducible strains are similar to other mixotrophic dinoflagellates, whereas toxic strains may consume organic matter and detritus, produce toxins and attack fish. In our model formulation we represent these differences in a simplified way: the non-inducible strain is kleptochloroplastidic and it can take up DIN, but it cannot utilize DON, whereas the toxic strain is heterotrophic, it cannot utilize DIN, but it can utilize DON directly. These differences give rise to very different impacts on prey and nutrient concentrations in our model. Under high DIN/DON ratio conditions, the non-inducible cells grew much faster and were therefore more likely to bloom, but this advantage is substantially mitigated when the DIN/DON ratio is low. A turbulence parameterization was also incorporated into our model. The effect of this was to reduce the grazing rate of Pfiesteria when turbulence levels are high. According to our model, increased turbulence is more detrimental to the toxic functional type because it grows more slowly. The further imposition of microzooplankton grazing in the model showed that top-down control effects can be very significant, which is consistent with both laboratory and field studies and the general idea that plankton blooms can only happen in the absence of substantial grazing control. In general, our model results suggest that non-toxic blooms are more likely to occur in more turbulent inorganic-nutrient rich conditions, which are often found in more open coastal and estuarine waters that are subject to high inorganic loading. In contrast, toxic blooms are more likely to occur in calm, organic-nutrient rich conditions, which are often found in shallow, protected tributaries that are subject to high organic nutrient loading. Our model results also support the idea that the absence of strong grazing pressure is a prerequisite to bloom formation for both non-inducible and toxic strains of Pfiesteria. These results are generally consistent with observed patterns of toxic Pfiesteria blooms in Chesapeake Bay, the Neuse River of North Carolina and many other coastal and estuarine environments.     

Applicability of Hydrogen Peroxide in Brown Tide Control – Culture and Microcosm Studies

Brown tide algal blooms, caused by the excessive growth of Aureococcus anophagefferens, recur in several northeastern US coastal bays. Direct bloom control could alleviate the ecological and economic damage associated with bloom outbreak. This paper explored the effectiveness and safety of natural chemical biocide hydrogen peroxide (H₂O₂) for brown tide bloom control. Culture studies showed that H₂O₂ at 1.6 mg L⁻¹ effectively eradicated high density A. anophagefferens within 24-hr, but caused no significant growth inhibition in the diatoms, prymnesiophytes, green algae and dinoflagellates of >2–3 μm cell sizes among 12 phytoplankton species tested over 1-week observation. When applied to brown tide bloom prone natural seawater in a microcosm study, this treatment effectively removed the developing brown tide bloom, while the rest of phytoplankton assemblage (quantified via HPLC based marker pigment analyses), particularly the diatoms and green algae, experienced only transient suppression then recovered with total chlorophyll a exceeding that in the controls within 72-hr; cyanobacteria was not eradicated but was still reduced about 50% at 72-hr, as compared to the controls. The action of H₂O₂ against phytoplankton as a function of cell size and cell wall structure, and a realistic scenario of H₂O₂ application were discussed.     

Karenia brevis causes high mortality and impaired swimming behavior of Florida stone crab larvae

The dinoflagellate Karenia brevis causes harmful algal blooms commonly referred to as red tides that are prevalent along Florida’s gulf coast. Severe blooms often cause fish kills, turbid water, and hypoxic events all of which can negatively impact local fisheries. The stone crab, Menippe mercenaria, is a ˜$25 million per year fishery that occurs primarily along Florida’s gulf coast. On the west Florida shelf, red tides occur from fall through spring, although severe blooms can occur during the summer. During the summer, stone crabs are reproductive and release larvae that are transported offshore where K. brevis blooms originate. This study determined the effects of K. brevis exposure on the survivorship, vertical swimming behavior, and oxygen consumption of stage-1 larval stone crabs. Survivorship was determined by exposing larvae to high (> 1 × 10⁶ cells L⁻¹) and medium (˜1 × 10⁵ cells L⁻¹) K. brevis concentrations for 96-hrs and were compared to controls that had no algae present. Larval swimming behavior (i.e., geotaxis) and oxygen consumption were monitored after 6-hr exposure to K. brevis. After 96-hrs of exposure, mortality was 100% and 30% for larvae in the high and medium concentrations of K. brevis, respectively, relative to the control. Larval swimming behavior was reversed in the K. brevis treatment; however oxygen consumption rates did not differ among treatments. These results suggest that severe blooms during the summer may reduce larval supply and serve as a potential bottleneck for new individuals recruiting into the fishery in years following a K. brevis bloom.     

Relative Uptake of Urea and Ammonium by Dinoflagellates or Cyanobacteria in Shrimp Mesocosms

The relative role of the organic nitrogen source, urea, versus ammonium as a nitrogen source for two species of dinoflagellates was compared with one species of cyanobacteria. Experiments were conducted opportunistically in nutrient-rich marine water during blooms of 34either cyanobacteria or dinoflagellates in outdoor mesocosms. These replicate mesocosms, which were stocked with shrimp fed high-protein formulated feeds, contained high biomasses of phytoplankton (mean chlorophyll a concentrations, 439.2–811.2 μg l⁻¹). ¹⁵N-urea and ammonium uptake rates for dinoflagellate-dominated blooms (Gymnodinium pulchellum-complex (Larsen), Karlodinium micrum (Larsen) (Dinophyceae)) were compared with blooms of the cyanobacterium, Romeria sp. (Cyanophyceae) in mesocosms with mean urea and ammonium concentrations ranging from 2.32 to 3.24 μM, and 7.39 to 64.85 μM, respectively. Urea uptake rates were significantly (p < 0.005) lower than ammonium uptake rates irrespective of which algal species dominated the bloom. Additionally urea uptake rates were not significantly higher in G. pulchellum-complex or K. micrum-dominated blooms than in Romeria sp. blooms. These results suggest that G pulchellum complex and K. micrum may not be gaining a competitive advantage in waters high in dissolved organic matter simply by preferentially utilizing urea. The periodic dominance of these species in highly organic environments, such as shrimp ponds, is likely to have a more complex explanation.     

Diurnal changes in zooplankton respiration rates and the phytoplankton activity in two Chilean lakes

Phytoplankton spatial distribution patterns in the Abra of Bilbao (a semienclosed coastal body of water) and adjacent shelf waters have been studied during June–July 1983 and May–June 1984. Small naked dinoflagellates, cryptophyceans and an unidentified nanoplankton component, were a common feature in all surveys. In July 1983 a dense bloom of nanoplankton developed inside the Abra which, in contrast to the community in the adhacent waters, contained high densities of small diatoms, naked dinoflagellates, cryptophyceans and the Haptophyta Phaeocystis pouchetii. Microplankton was mainly composed of dinoflagellates in July 1983, and of diatoms in June 1983 and May–June 1984. Microplankton abundance was highest in May–June 1984 and decreased from the shelf to the Abra. A principal component analysis performed separately on each cruise revealed the differences in the structure of the phytoplankton community between the Abra of Bilbao and the adjacent shelf waters.     

Red tide assemblage formation in an estuarine upwelling ecosystem: Ria de Vigo

Red tides are conspicuous in the upwelling system of Galicia(NW Iberian Peninsula). At present, there are conflicting hypothesesabout the generation site of these phytoplankton assemblages.It is interesting to know whether the rias can be sites of redtide formation or if they act only as accumulation sites ofpopulations advected from shelf waters. A study in the Ra deVigo, carried out during late September 1990, showed the developmentof a red tide assemblage, composed of Alexandrium affinis, Ceraiiumfusus and Gymnodinium catenaium, during a 2 week upwelling-downwellingcycle. Growth occurred at the bottom of the thermocline-topof the nutricline. Above this assemblage, a diatom assemblage(large diatoms) was blooming. Prior to the formation of thered tide, a subsurface chlorophyll maximum made up of smalldiatoms (Nilzschia f. seriaia, Chaeloceros socialis), smallflagellates (<30 µm) and small gymnodinid forms (<30µm) was observed. In the nutrient-depleted upper layer,several autotrophic and large heterotrophic dinoflagellatesdominated. It is suggested that the ratio between the velocityof upward water movement and the depth of the stratified upperlayer (flushing rate, day^–1) is the critical parameterwhich triggers active phytoplankton growth. It can be concludedthat upward water velocities of {small tilde}2.5 m day^–1and a stratified upper layer of 10 m depth (flushing rate 0.25day^–1) are the main physical constraints for red tidedevelopment.     

Environmental exposures to Florida red tides: Effects on emergency room respiratory diagnoses admissions

Human exposure to Florida red tides formed by Karenia brevis, occurs from eating contaminated shellfish and inhaling aerosolized brevetoxins. Recent studies have documented acute symptom changes and pulmonary function responses after inhalation of the toxic aerosols, particularly among asthmatics. These findings suggest that there are increases in medical care facility visits for respiratory complaints and for exacerbations of underlying respiratory diseases associated with the occurrence of Florida red tides.This study examined whether the presence of a Florida red tide affected the rates of admission with a respiratory diagnosis to a hospital emergency room in Sarasota, FL. The rate of respiratory diagnoses admissions were compared for a 3-month time period when there was an onshore red tide in 2001 (red tide period) and during the same 3-month period in 2002 when no red tide bloom occurred (non-red tide period). There was no significant increase in the total number of respiratory admissions between the two time periods. However, there was a 19% increase in the rate of pneumonia cases diagnosed during the red tide period compared with the non-red tide period. We categorized home residence zip codes as coastal (within 1.6 km from the shore) or inland (>1.6 km from shore). Compared with the non-red tide period, the coastal residents had a significantly higher (54%) rate of respiratory diagnoses admissions than during the red tide period. We then divided the diagnoses into subcategories (i.e. pneumonia, bronchitis, asthma, and upper airway disease). When compared with the non-red tide period, the coastal zip codes had increases in the rates of admission of each of the subcategories during the red tide period (i.e. 31, 56, 44, and 64%, respectively). This increase was not observed seen in the inland zip codes.These results suggest that the healthcare community has a significant burden from patients, particularly those who live along the coast, needing emergency medical care for both acute and potentially chronic respiratory illnesses during red tide blooms.