Brevis Blooms Research Articles

Brevenal, a brevetoxin antagonist from Karenia brevis, binds to a previously unreported site on mammalian sodium channels

Brevetoxins are a family of ladder-frame polyether toxins produced by the marine dinoflagellate Karenia brevis. During blooms of K. brevis, inhalation of brevetoxins aerosolized by wind and wave action can lead to asthma-like symptoms in persons at the beach. Consumption of either shellfish or finfish contaminated by K. brevis blooms can lead to the development of neurotoxic shellfish poisoning. The toxic effects of brevetoxins are due to binding at a defined site on, and subsequent activation of, voltage-sensitive sodium channels (VSSCs) in cell membranes (site 5). In addition to brevetoxins, K. brevis produces several other ladder-frame compounds. One of these compounds, brevenal, has been shown to antagonize the effects of brevetoxin. In an effort to further characterize the effects of brevenal, a radioactive analog ([3H]-brevenol) was produced by reducing the terminal aldehyde moiety of brevenal to an alcohol using tritiated sodium borohydride. A KD of 67nM and Bmax of 7.1pmol/mg protein were obtained for [3H]-brevenol in rat brain synaptosomes, suggesting a 1:1 matching with VSSCs. Brevenal and brevenol competed for [3H]-brevenol binding with Ki values of 75nM and 56nM, respectively. However, although both brevenal and brevenol inhibited brevetoxin binding, brevetoxin was completely ineffective at competition for [3H]-brevenol binding. After examining other site-specific compounds, it was determined that [3H]-brevenol binds to a site that is distinct from the other known sites on the sodium channel, including the brevetoxin site, (site 5) although some interaction with site 5 is apparent.

Increased toxicity of Karenia brevis during phosphate limited growth: ecological and evolutionary implications.

Karenia brevis is the dominant toxic red tide algal species in the Gulf of Mexico. It produces potent neurotoxins (brevetoxins [PbTxs]), which negatively impact human and animal health, local economies, and ecosystem function. Field measurements have shown that cellular brevetoxin contents vary from 1–68 pg/cell but the source of this variability is uncertain. Increases in cellular toxicity caused by nutrient-limitation and inter-strain differences have been observed in many algal species. This study examined the effect of P-limitation of growth rate on cellular toxin concentrations in five Karenia brevis strains from different geographic locations. Phosphorous was selected because of evidence for regional P-limitation of algal growth in the Gulf of Mexico. Depending on the isolate, P-limited cells had 2.3- to 7.3-fold higher PbTx per cell than P-replete cells. The percent of cellular carbon associated with brevetoxins (%C-PbTx) was ∼ 0.7 to 2.1% in P-replete cells, but increased to 1.6–5% under P-limitation. Because PbTxs are potent anti-grazing compounds, this increased investment in PbTxs should enhance cellular survival during periods of nutrient-limited growth. The %C-PbTx was inversely related to the specific growth rate in both the nutrient-replete and P-limited cultures of all strains. This inverse relationship is consistent with an evolutionary tradeoff between carbon investment in PbTxs and other grazing defenses, and C investment in growth and reproduction. In aquatic environments where nutrient supply and grazing pressure often vary on different temporal and spatial scales, this tradeoff would be selectively advantageous as it would result in increased net population growth rates. The variation in PbTx/cell values observed in this study can account for the range of values observed in the field, including the highest values, which are not observed under N-limitation. These results suggest P-limitation is an important factor regulating cellular toxicity and adverse impacts during at least some K. brevis blooms.

Satellite-Observed Black Water Events off Southwest Florida: Implications for Coral Reef Health in the Florida Keys National Marine Sanctuary

A “black water” event, as observed from satellites, occurred off southwest Florida in 2012. Satellite observations suggested that the event started in early January and ended in mid-April 2012. The black water patch formed off central west Florida and advected southward towards Florida Bay and the Florida Keys with the shelf circulation, which was confirmed by satellite-tracked surface drifter trajectories. Compared with a previous black water event in 2002, the 2012 event was weaker in terms of spatial and temporal coverage. An in situ survey indicated that the 2012 black water patch contained toxic K. brevis and had relatively low CDOM (colored dissolved organic matter) and turbidity but high chlorophyll-a concentrations, while salinity was somewhat high compared with historical values. Further analysis revealed that the 2012 black water was formed by the K. brevis bloom initiated off central west Florida in late September 2011, while river runoff, Trichodesmium and possibly submarine groundwater discharge also played important roles in its formation. Black water patches can affect benthic coral reef communities by decreasing light availability at the bottom, and enhanced nutrient concentrations from black water patches support massive macroalgae growth that can overgrow coral reefs. It is thus important to continue the integrated observations where satellites provide synoptic and repeated observations of such adverse water quality events.

Comparative analysis of three brevetoxin-associated bottlenose dolphin (Tursiops truncatus) mortality events in the Florida Panhandle region (USA).

In the Florida Panhandle region, bottlenose dolphins (Tursiops truncatus) have been highly susceptible to large-scale unusual mortality events (UMEs) that may have been the result of exposure to blooms of the dinoflagellate Karenia brevis and its neurotoxin, brevetoxin (PbTx). Between 1999 and 2006, three bottlenose dolphin UMEs occurred in the Florida Panhandle region. The primary objective of this study was to determine if these mortality events were due to brevetoxicosis. Analysis of over 850 samples from 105 bottlenose dolphins and associated prey items were analyzed for algal toxins and have provided details on tissue distribution, pathways of trophic transfer, and spatial-temporal trends for each mortality event. In 1999/2000, 152 dolphins died following extensive K. brevis blooms and brevetoxin was detected in 52% of animals tested at concentrations up to 500 ng/g. In 2004, 105 bottlenose dolphins died in the absence of an identifiable K. brevis bloom; however, 100% of the tested animals were positive for brevetoxin at concentrations up to 29,126 ng/mL. Dolphin stomach contents frequently consisted of brevetoxin-contaminated menhaden. In addition, another potentially toxigenic algal species, Pseudo-nitzschia, was present and low levels of the neurotoxin domoic acid (DA) were detected in nearly all tested animals (89%). In 2005/2006, 90 bottlenose dolphins died that were initially coincident with high densities of K. brevis. Most (93%) of the tested animals were positive for brevetoxin at concentrations up to 2,724 ng/mL. No DA was detected in these animals despite the presence of an intense DA-producing Pseudo-nitzschia bloom. In contrast to the absence or very low levels of brevetoxins measured in live dolphins, and those stranding in the absence of a K. brevis bloom, these data, taken together with the absence of any other obvious pathology, provide strong evidence that brevetoxin was the causative agent involved in these bottlenose dolphin mortality events.

Development of a competitive fluorescence-based synaptosome binding assay for brevetoxins

Brevetoxins are a family of ladder-frame polyether toxins produced during blooms of the marine dinoflagellate Karenia brevis. Inhalation of brevetoxins aerosolized by wind and wave action can lead to asthma-like symptoms in beach goers. Consumption of either shellfish or finfish exposed to K. brevis blooms can lead to the development of neurotoxic shellfish poisoning. The toxic effects of brevetoxins are due to activation of voltage-sensitive sodium channels (VSSCs) in cell membranes. Binding of brevetoxin analogs and competitors to site 5 on these channels has historically been measured using a radioligand competition assay that is fraught with difficulty, including slow analysis time, production of radioactive waste, and cumbersome and expensive methods associated with the generation of radioactive labeled ligands. In this study, we describe the development of a novel fluorescent synaptosome binding assay for the brevetoxin receptor. BODIPY®-conjugated to PbTx-2 was used as the labeled ligand. The BODIPY®–PbTx-2 conjugate was found to displace [3H]–PbTx-3 from its binding site on VSSCs on rat brain synaptosomes with an equilibrium inhibition constant of 0.11nM. We have shown that brevetoxin A and B analogs are all able to compete for binding with the fluorescent ligand. Most importantly, this assay was validated against the current site 5 receptor binding assay standard, the radioligand receptor assay for the brevetoxin receptor using [3H]–PbTx-3 as the labeled ligand. The fluorescence based assay yielded equilibrium inhibition constants comparable to the radioligand assay for all brevetoxin analogs. The fluorescence based assay was quicker, far less expensive, and did not generate radioactive waste or need radioactive facilities. As such, this fluorescence-based assay can be used to replace the current radioligand assay for site 5 on voltage-sensitive sodium channels and will be a vital tool for future experiments examining the binding affinity of various ligands for site 5 on sodium channels.

Trophic transfer of brevetoxins to the benthic macrofaunal community during a bloom of the harmful dinoflagellate Karenia brevis in Sarasota Bay, Florida

Harmful algal blooms can cause mass mortalities of top predators such as fish, marine mammals and seabirds but the food web transfer from toxic phytoplankton to these organisms has not been fully elucidated. Macrobenthic invertebrates in coastal waters, including bivalve suspension- and deposit-feeders, carnivorous gastropods, deposit-feeding amphipods and polychaetes, are a major food source for a wide variety of predators and can thus play a critical role in the trophic transfer of algal toxins to higher trophic levels. The objective of this study was to investigate toxin accumulation in transplanted juvenile hard clams, Mercenaria mercenaria, a species naturally occurring in the region, and in various macrobenthic functional groups from Florida coastal waters during a natural bloom of the dinoflagellate, Karenia brevis, a producer of brevetoxins. Bloom concentrations in the water column ranged from 100 to 1200cellsml−1 over the course of the experiment. This study revealed that these lipophilic toxins can be rapidly accumulated by both suspension- and deposit-feeding benthos, especially bivalve molluscs [1.9–2.8μg PbTx-3 eq (g wet weight)−1]. Transplanted M. mercenaria rapidly accumulated toxins from the water column attaining ∼0.5μg PbTx-3 eq (g wet tissue)−1 after only 4h-exposure to the K. brevis bloom and a maximum value of 1.5±0.2μg PbTx-3 eq (g wet tissue)−1 after 72h. Relatively high brevetoxin concentrations were also measured in co-occurring benthic carnivorous gastropods [1–2.6μg PbTx-3 eq (g wet weight, WW)−1]. Mean toxin concentrations in polychaetes and crustaceans varied in the range ∼0.04–0.2μg PbTx-3 eq (g WW)−1 over the study period, and thus were typically lower than in molluscs. This study demonstrated in situ toxin accumulation by benthic primary and secondary consumers during a natural Florida red tide. Accumulation by primary consumers may be highly variable in space and time (as shown in bivalves from the natural benthic community) and among taxonomic groups. Toxin transfer further up the food web will thus depend on the toxin level accumulated in prey, the number of pathways from which the predator may accumulate toxins and on possible biological magnification of lipophilic toxins. Overall, this study revealed qualitatively and quantitatively that benthic consumers of a number of taxa can serve as vectors for transporting brevetoxins within the food web.

Karenia brevis red tides and brevetoxin-contaminated fish: a high risk factor for Florida’s scavenging shorebirds?

Shorebirds, including sanderlings ( Calidris alba ) and ruddy turnstones ( Arenaria interpres ), were observed scavenging beached fish, such as thread herring ( Opisthonema oglinum ), scaled sardine ( Harengula jaguana ) and mullet ( Mugil spp.) killed during a 2005 Karenia brevis red tide along the central west coast of Florida. Brevetoxin concentrations in dead fish tissues were analyzed to determine the potential exposure risk to scavenging shorebirds. This component of brevetoxin cycling in the food web has not previously been explored and the risks or benefits of this behavior for shorebirds are not currently understood. Toxin levels in freshly dead fish tissues ranged from 32 to 95,753 ng PbTx g -1 . Brevetoxins in shorebird livers were also confirmed (26–1313 ng PbTx g -1 ) in dead birds collected opportunistically from local beaches and rehabilitation centers during the red tide event, suggesting that brevetoxin exposure is a risk factor for mortality. These findings underscore the need to assess the ecological impacts of K. brevis blooms on Florida’s migratory and resident shorebird populations.

Resolving DOM fluorescence fractions during a Karenia brevis bloom patch on the Southwest Florida Shelf

Organic matter can be supplied naturally from land through rivers or produced in-situ in the marine environment. Current methods of examining natural bulk dissolved organic matter (DOM) are not able to discriminate multiple sources of DOM. A diagnostic tool to identify DOM sources is critical to determine possible sources of organic nutrients that influence K. brevis harmful algal bloom (HAB) development. This study applied multi-wavelength fluorescence coupled with a supervised pattern recognition technique (e.g., parallel factorial analysis (PARAFAC) using samples collected from river, estuary and shelf waters where the toxic dinoflagellate Karenia brevis off of Sanibel Island, Florida was observed. The PARAFAC model distinguished four different fractions of DOM components containing humic-like and protein-like components. The derived terrestrial humic-like material was indicative of land-based sources while the tryptophan-like component was likely produced from in-situ biological production. The study developed and tested the hypothesis that the direct relationship of the protein-like DOM fluorescence with K. brevis cell density indicated that the bloom patch was most likely supported by organic nutrients produced in-situ. The results demonstrated that multi-wavelength fluorescence analysis coupled with PARAFAC modeling technique simultaneously resolved DOM fluorescence fractions and their possible sources—information that are critical in explaining harmful algal bloom formation.

Co-occurrence of multiple classes of harmful algal toxins in bottlenose dolphins ( Tursiops truncatus) stranding during an unusual mortality event in Texas, USA

During February–April 2008, an unusual mortality event occurred in Texas coastal waters that resulted in over 100 bottlenose dolphin ( Tursiops truncatus) deaths. This mortality event overlapped spatially and temporally with a harmful algal bloom (HAB) composed of the toxin-producing genera Dinophysis spp. and Prorocentrum spp., and was associated with shellfish bed closures due to HAB toxins. A bloom of the toxin-producing diatom Pseudo- nitzschia pungens was also detected in Texas coastal waters in early April, towards the end of the dolphin mortality event. Analysis of dolphin gastrointestinal contents collected during this event demonstrated the presence of the HAB toxins domoic acid and okadaic acid in association with these blooms, as well as evidence of brevetoxin exposure in the absence of an associated K. brevis bloom. Historical dolphin stranding data for Texas waters indicate seasonal stranding peaks similar to the present study, indicating a need for investigating potential HAB involvement in mass strandings in previous years and in future events. This study marks the first reported occurrence of okadaic acid in marine mammals, and documents a unique co-occurrence of multiple HAB toxins associated with an unusual mortality event. Texas waters harbor a high diversity of HAB events relative to other coastal regions, and this study highlights the importance of efforts to understand the impacts of such HAB events on the health of Texas marine wildlife.

Effects of a Persistent Red Tide (Karenia brevis) Bloom on Community Structure and Species-Specific Relative Abundance of Nekton in a Gulf of Mexico Estuary

An unusually persistent red tide event caused by the ichthyotoxic dinoflagellate Karenia brevis occurred along the southwest Florida coast in 2005. Extensive fish kills led to concerns regarding the effect of red tide on fish populations and their subsequent recruitment. Community structure differences were analyzed for all small- and large-bodied nekton species collected by fisheries-independent monitoring from 1996 through 2006. Indices of abundance of five economically important fish species were also calculated from this time period. A significant change in small- and large-bodied nekton community structure was apparent from summer 2005 through spring 2006. Declines in the annual recruitment of juvenile spotted seatrout (Cynoscion nebulosus), sand seatrout (Cynoscion arenarius), and red drum (Sciaenops ocellatus) were evident in 2005 and 2006. Species-specific subadult and adult abundances, however, were consistent with those of previous years. These community shifts and species-specific declines appear to be associated with the red tide event.

Photodegradation of the brevetoxin PbTx‐2 in coastal seawater

The photodegradation rate of the brevetoxin analog PbTx‐2 was investigated in a variety of natural water matrices. The observed first‐order photodegradation rate coefficient of the logarithmic‐transformed dissolved PbTx‐2 concentrations vs. irradiation time was 0.20 ± 0.04 h−1 in coastal seawater, corresponding to a half‐life of approximately 3 h based on 10 separate photolysis experiments. No loss of PbTx‐2 occurred in dark controls, indicating that this was primarily a photo‐mediated process. Photodegradation rate coefficients in samples in which dissolved organic matter was removed by ultraviolet oxidation prior to photolysis resulted in significantly slower rates of PbTx‐2 photodegradation (0.08 ± 0.03 h−1). When trace metals were also removed prior to photolysis, no loss of PbTx‐2 occurred, indicating that direct photolytic loss of PbTx‐2 is insignificant in coastal seawater. The proposed mechanism of PbTx‐2 decay is a photosensitized pathway involving organic matter and trace metals that is significantly accelerated by decreasing oxygen concentrations. The influence of molecular oxygen on the rate of toxin loss has important ramifications for the fate of PbTx‐2 during Karenia brevis blooms, as in situ dissolved O2 concentrations fluctuate widely during bloom development and decay. Sunlight‐mediated reactions are therefore a significant, yet previously unrecognized, sink of dissolved PbTx‐2 in seawater under environmentally relevant conditions.

Long-term evaluation of three satellite ocean color algorithms for identifying harmful algal blooms ( Karenia brevis) along the west coast of Florida: A matchup assessment

We present a simple algorithm to identify Karenia brevis blooms in the Gulf of Mexico along the west coast of Florida in satellite imagery. It is based on an empirical analysis of collocated matchups of satellite and in situ measurements. The results of this Empirical Approach is compared to those of a Bio-optical Technique – taken from the published literature – and the Operational Method currently implemented by the NOAA Harmful Algal Bloom Forecasting System for K. brevis blooms. These three algorithms are evaluated using a multi-year MODIS data set (from July, 2002 to October, 2006) and a long-term in situ database. Matchup pairs, consisting of remotely-sensed ocean color parameters and near-coincident field measurements of K. brevis concentration, are used to assess the accuracy of the algorithms. Fair evaluation of the algorithms was only possible in the central west Florida shelf (i.e. between 25.75°N and 28.25°N) during the boreal Summer and Fall months (i.e. July to December) due to the availability of valid cloud-free matchups. Even though the predictive values of the three algorithms are similar, the statistical measure of success in red tide identification (defined as cell counts in excess of 1.5 × 10 4 cells L −1) varied considerably (sensitivity— Empirical: 86%; Bio-optical: 77%; Operational: 26%), as did their effectiveness in identifying non-bloom cases (specificity— Empirical: 53%; Bio-optical: 65%; Operational: 84%). As the Operational Method had an elevated frequency of false-negative cases (i.e. presented low accuracy in detecting known red tides), and because of the considerable overlap between the optical characteristics of the red tide and non-bloom population, only the other two algorithms underwent a procedure for further inspecting possible detection improvements. Both optimized versions of the Empirical and Bio-optical algorithms performed similarly, being equally specific and sensitive (~ 70% for both) and showing low levels of uncertainties (i.e. few cases of false-negatives and false-positives: ~ 30%)—improved positive predictive values (~ 60%) were also observed along with good negative predictive values (~ 80%).

Compositional changes in neurotoxins and their oxidative derivatives from the dinoflagellate, Karenia brevis, in seawater and marine aerosol.

The harmful alga, Karenia brevis, produces a suite of polyether neurotoxins, brevetoxins or PbTx, that cause marine animal mortality and neurotoxic shellfish poisoning (NSP). A characteristic of K. brevis blooms is associated airborne toxins that result in severe respiratory problems. This study was undertaken to determine the composition of aerosolized brevetoxins and oxidative derivatives to which beachgoers are exposed during a K. brevis bloom. The suite of brevetoxins and derivatives in seawater is comprised of intra-cellular (IC) and extra-cellular (EC) compounds. We hypothesized that aerosolized compounds are generated primarily from EC, hydrophobic compounds in seawater by bubble-mediated transport. Thus the composition of aerosolized brevetoxins and derivatives, to which beachgoers are exposed, would reflect the EC composition of the source matrix (the local surf zone). Brevetoxins were extracted from water collected along the shore and from marine aerosols along Siesta Beach and Lido Beach in Sarasota, FL, USA, during K. brevis blooms. Water samples were further processed into IC and EC components. The primary brevetoxins observed in water and air included PbTx-1, -2, -3, -PbTx-2-carboxylic acid, and brevenal. Oxidation and/or hydrolysis products of PbTx-1, -2, -3 and -7 were also found in EC water and in aerosol, but not IC.

Lagrangian particle tracking of a toxic dinoflagellate bloom within the Tampa Bay estuary

A coastal risk assessment system simulates the basic physical mechanisms underlying contaminant transport in Tampa Bay. This risk assessment system, comprised of a three-dimensional numerical circulation model coupled to a Lagrangian particle tracking model, simulates the transport and dispersion of a toxic dinoflagellate bloom. Instantaneous velocity output from the circulation model drives the movement of particles, each representing a fraction of a K. brevis bloom, within the model grid cells. Hindcast simulations of the spatial distribution of the K. brevis bloom are presented and compared with water sample concentrations collected during the peak of the bloom. Probability calculations, herein called transport quotients, allow for rapid analysis of bay-wide K. brevis transport showing locations most likely to be impacted by the contaminant. Maps constructed from the transport quotients provide managers with a bay-wide snapshot of areas in Tampa Bay most at risk during a hazardous bloom event.

Comparative analysis of bacterioplankton assemblages from Karenia brevis bloom and nonbloom water on the west Florida shelf (Gulf of Mexico, USA) using 16S rRNA gene clone libraries

The brevetoxin-producing dinoflagellate, Karenia brevis, forms nearly annual blooms off the Florida west coast, severely impacting the region's ecology and economy. Bacteria are often cited as either promoting or interfering with the development of algal blooms, and thus a detailed study of the bacterioplankton assemblages associated with K. brevis was undertaken. We developed sixteen 16S rRNA gene clone libraries from K. brevis bloom and adjacent nonbloom water to determine the bacterial groups present and assess the influence of K. brevis cell number and/or depth on bacterioplankton community composition. Most notably, bacterial groups such as Rhodobacterales (Alphaproteobacteria) and Cytophagales/Sphingobacteriales (Bacteroidetes), reported previously to be associated with other harmful algal species, were often abundant in the presence of K. brevis. Cyanobacteria frequently dominated surface samples containing no detectable K. brevis, consistent with earlier work suggesting that these photosynthetic organisms may be important in promoting the proliferation of these blooms by conditioning the water. Moreover, differences in the abundance/diversity of traditionally more rare and often undocumented phylogenetic groups (e.g. Betaproteobacteria, Deltaproteobacteria, Chloroflexus, Firmicutes) were apparent in bloom vs. nonbloom water. This is the first study to document the association of these phylogenetic groups with natural K. brevis populations and suggests a potential role for these microorganisms in K. brevis bloom dynamics.

A historical analysis of the potential nutrient supply from the N2 fixing marine cyanobacterium Trichodesmium spp. to Karenia brevis blooms in the eastern Gulf of Mexico

Blooms of Karenia brevis co-occur with populations of the N2 fixing cyanobacterium Trichodesmium on the West Florida shelf where iron (Fe) and phosphorus (P) supplies have been shown to control the growth potential of these cyanophytes. Historical data records of Trichodesmium presence and abundance (1960–2008) were analyzed in relation to the nutrient requirements of annually coincident K. brevis blooms, focusing on the potential direct supply of nitrogen (N) via N2-fixation with subsequent excretion of recently fixed N2 as NH4+ and dissolved organic nitrogen and indirect transfer from Trichodesmium biomass (as particulate N and P) during cell death. While release of “new” N from biological N2-fixation can supply up to 40% of the 2001 large red tide (9.5 × 106 cells L−1), estimates of the total N available, including the regeneration of additional nutrients supplied from particulate stocks aggregated within surface populations of observed Trichodesmium biomass during cell death, suggest that up to 100% of N and P requirements of such large blooms can be met from N2-fixation sources.

Eosinophilia and biotoxin exposure in bottlenose dolphins (Tursiops truncatus) from a coastal area impacted by repeated mortality events

Bottlenose dolphins (Tursiops truncatus) inhabiting coastal waters in the northern Gulf of Mexico have been impacted by recurrent unusual mortality events over the past few decades. Several of these mortality events along the Florida panhandle have been tentatively attributed to poisoning from brevetoxin produced by the dinoflagellate Karenia brevis. While dolphins in other regions of the Florida coast are often exposed to K. brevis blooms, large-scale dolphin mortality events are relatively rare and the frequency and magnitude of die-offs along the Panhandle raise concern for the apparent vulnerability of dolphins in this region. We report results from dolphin health assessments conducted near St. Joseph Bay, Florida, an area impacted by 3 unusual die-offs within a 7-year time span. An eosinophilia syndrome, manifested as an elevated blood eosinophil count without obvious cause, was observed in 23% of sampled dolphins. Elevated eosinophil counts were associated with decreased T-lymphocyte proliferation and increased neutrophil phagocytosis. In addition, indication of chronic low-level exposure to another algal toxin, domoic acid produced by the diatom Pseudo-nitzschia spp., was determined. Previous studies of other marine mammal populations exposed recurrently to Pseudo-nitzschia blooms have suggested a possible link between the eosinophilia and domoic acid exposure. While the chronic eosinophilia syndrome could over the long-term produce organ damage and alter immunological status and thereby increase vulnerability to other challenges, the significance of the high prevalence of the syndrome to the observed mortality events in the St. Joseph Bay area is unclear. Nonetheless, the unusual immunological findings and concurrent evidence of domoic acid exposure in this sentinel marine species suggest a need for further investigation to elucidate potential links between chronic, low-level exposure to algal toxins and immune health.

Neurochemical alterations in lemon shark ( Negaprion brevirostris) brains in association with brevetoxin exposure

Brevetoxins are persistent, bioaccumulative, lipophilic polyether neurotoxins synthesized by Karenia brevis, a harmful algal bloom (HAB) dinoflagellate. Although some marine organisms accumulate potentially harmful levels of brevetoxins, little is known about neurotoxic effects in wild populations. Here, tissue (i.e., liver, kidney, muscle, intestine, gill, brain) brevetoxin levels (as ng PbTx-3 eq/g) and four neurochemical biomarkers (monoamine oxidase, MAO; cholinesterase, ChE; muscarinic cholinergic receptor, mAChR; N-methyl- d-aspartic acid receptor, NMDAR) were compared between eleven lemon sharks collected during a K. brevis bloom and eighteen lemon sharks not exposed to a bloom (controls) in a case–control manner. Brevetoxin levels in tissues were significantly higher in HAB-exposed sharks when compared to controls, and tissue levels (e.g., 277–3112 ng/g in livers, 429–2833 ng/g in gills) in HAB-exposed sharks were comparable to levels detected in a shark (e.g., 1223 ng/g in liver, 930 ng/g in gill) that died presumably of toxin exposure. Further, there were significant correlations between brain brevetoxin levels and ChE activity ( r = −0.41; p < 0.05), MAO activity ( r = −0.37; p < 0.05), mAChR levels ( r = 0.55; p < 0.01), and NMDAR levels ( r = −0.49; p < 0.01). There were no relationships between neurochemical biomarkers and metals (total mercury, methylmercury, selenium). Overall, these results in tissues from free-ranging lemon sharks indicate that ecologically relevant exposures to brevetoxins may cause significant changes in brain neurochemistry. As disruptions to neurochemistry precede structural and functional damage to the nervous system, these results suggest that relevant exposures to HABs may be causing sub-clinical effects in lemon sharks and raise further questions about the ecological and physiological impacts of HABs on marine biota.

Brevetoxins in sharks and rays (Chondrichthyes, Elasmobranchii) from Florida coastal waters

In October 2000, a mass mortality of blacktip sharks (Carcharhinus limbatus) and Atlantic sharpnose sharks (Rhizoprionodon terraenovae) in northwest Florida occurred in conjunction with a Karenia brevis red tide bloom. Before this incident, no information existed on red tide-induced shark mortalities or baseline brevetoxin levels in sharks and rays from red tide-endemic areas. We report here that brevetoxin accumulation in live and red tide-killed elasmobranchs is common during K. brevis blooms and non-bloom periods. Strong relationships were found between the frequency of red tide blooms and the average brevetoxin concentrations in elasmobranch tissues. The presence of brevetoxins in Atlantic coast sharks in the absence of documented K. brevis blooms may suggest that blooms are occurring in areas that are not well monitored. Although red tide-related shark mortalities are rarely observed, the presence of brevetoxins in shark embryos raises questions about the effects these toxins may have on the reproductive success of sharks.

Changes in work habits of lifeguards in relation to Florida red tide

The marine dinoflagellate, Karenia brevis, is responsible for Florida red tides. Brevetoxins, the neurotoxins produced by K. brevis blooms, can cause fish kills, contaminate shellfish, and lead to respiratory illness in humans. Although several studies have assessed different economic impacts from Florida red tide blooms, no studies to date have considered the impact on beach lifeguard work performance. Sarasota County experiences frequent Florida red tides and staffs lifeguards at its beaches 365 days a year. This study examined lifeguard attendance records during the time periods of March 1 to September 30 in 2004 (no bloom) and March 1 to September 30 in 2005 (bloom). The lifeguard attendance data demonstrated statistically significant absenteeism during a Florida red tide bloom. The potential economic costs resulting from red tide blooms were comprised of both lifeguard absenteeism and presenteeism. Our estimate of the costs of absenteeism due to the 2005 red tide in Sarasota County is about $3000. On average, the capitalized costs of lifeguard absenteeism in Sarasota County may be on the order of $100,000 at Sarasota County beaches alone. When surveyed, lifeguards reported not only that they experienced adverse health effects of exposure to Florida red tide but also that their attentiveness and abilities to take preventative actions decrease when they worked during a bloom, implying presenteeism effects. The costs of presenteeism, which imply increased risks to beachgoers, arguably could exceed those of absenteeism by an order of magnitude. Due to the lack of data, however, we are unable to provide credible estimates of the costs of presenteeism or the potential increased risks to bathers.