Brevetoxin Concentrations Research Articles

Emerging Insights into Brevetoxicosis in Sea Turtles.

This review summarizes the current understanding of how brevetoxins, produced by Karenia brevis during harmful algal blooms, impact sea turtle health. Sea turtles may be exposed to brevetoxins through ingestion, inhalation, maternal transfer, and potentially absorption through the skin. Brevetoxins bind to voltage-gated sodium channels in the central nervous system, disrupting cellular function and inducing neurological symptoms in affected sea turtles. Moreover, the current evidence suggests a broader and longer-term impact on sea turtle health beyond what is seen during stranding events. Diagnosis relies on the detection of brevetoxins in tissues and plasma from stranded turtles. The current treatment of choice, intravenous lipid emulsion therapy, may rapidly reduce symptoms and brevetoxin concentrations, improving survival rates. Monitoring, prevention, and control strategies for harmful algal blooms are discussed. However, as the frequency and severity of blooms are expected to increase due to climate change and increased environmental pollution, continued research is needed to better understand the sublethal effects of brevetoxins on sea turtles and the impact on hatchlings, as well as the pharmacokinetic mechanisms underlying brevetoxicosis. Moreover, research into the optimization of treatments may help to protect endangered sea turtle populations in the face of this growing threat.

Clam calamity: five concurrent cases of neurotoxic shellfish poisoning with varying presentations following ingestion of clams from Gulf of Mexico water contaminated with Karenia brevis confirmed by serum brevetoxin assays

Introduction Karinia brevis, a marine dinoflagellate, is the causative organism for “red-tide” on the east coast of Florida.This microbe produces brevetoxins, which bioaccumulate in filter feeding bivalve shellfish. In humans, inhalational exposure is common, while ingestion of contaminated shellfish is more rare. Ingested brevetoxin causes gastrointestinal and neurological symptoms collectively known as neurotoxic shellfish poisoning. Case cluster A group of tourists collected clams from a beach during a red tide event. The clams were soaked in brine, microwaved, and consumed for lunch. The index patient experienced seizure-like activity postprandially prompting the cohort to present for medical attention. Five people presented to the emergency department with neurotoxic shellfish poisoning-related symptoms. All patients received supportive care only. Symptoms resolved within 24 hours. Serum brevetoxin concentrations were reported for four patients. Discussion Ingestion of brevetoxin is rare but may become more common as the frequency and severity of “red-tide” events increase. In our cluster, each person consumed a different number of clams and presented with classic and some “non-classic” symptoms. A trend toward more severe symptoms with a larger number of clams ingested was observed. Conclusions This case cluster describes the clinical course of individuals after consumption of brevetoxin contaminated shellfish.

Preservation of brevetoxins in Southwest Florida coastal sediments

Florida red tide is a natural phenomenon caused by the dinoflagellate, Karenia brevis. Karenia brevis blooms produce potent toxins (brevetoxins) that can cause neurotoxic and respiratory illness in humans and marine life. Red tides were recorded by Spanish explorers as early as the 17th century, however published red tide studies before 1940 are unavailable. Recent studies have suggested that red tide events may be becoming more frequent, intense, and longer lasting, which may be linked to modern land development and changing water quality. While the scientific record of modern red tides is relatively short, the distributions and concentrations of chemical biomarkers (e.g., brevetoxins produced by K. brevis) in coastal-marine sediments can potentially be used to study historic red tides. This study aims to quantify the concentration and vertical distribution of brevetoxins in coastal Southwest Florida (SWFL) sediment cores in order to determine if downcore brevetoxins may potentially be used to reconstruct historic red tide events. Sediment samples were radiometrically dated using 210Pb and subsamples were analyzed utilizing liquid chromatography/triple quadrupole mass spectrometry (LC–MS/MS) for brevetoxin congeners, namely, PbTx-1, PbTx-2, PbTx-3, and PbTx-5. The 210Pb–dated sediment cores represent ∼60–80 years of brevetoxin accumulation and total brevetoxin (ΣPbTx) concentrations in sediment cores varied from below detection limits to 25.3 ng g − 1 of dry sediments. Highest concentrations were found in surficial sediments (top 0–3 cm) and may indicate brevetoxin preservation from the 2017–2019 red-tide event. The down-core preservation and variability of brevetoxin indicate its potential use as a chemical biomarker to assess long-term red tide intensities and frequencies. This research is a first step towards reconstructing historic red tide events from sedimentary chemical biomarkers and may allow for future assessment of the human impacts on red tide frequency, intensity and duration.

Characterization of Atmospheric Processes of Brevetoxins in Sea Spray Aerosols from Red Tide Events.

Atmospheric processes can affect the longevity of harmful toxins in sea spray aerosols (SSA). This study characterized the degradation of brevetoxin (BTx) in SSA under different environmental conditions. The samples of seawater collected during a Karenia brevis bloom in Manasota, Florida, were nebulized into a large outdoor photochemical chamber to mimic the atmospheric oxidation of aerosolized toxins and then aged in the presence or absence of sunlight and/or O3. Aerosol samples were collected during the aging process using a Particle-Into-Liquid Sampler. Their BTx concentrations were measured using an enzyme-linked immuno-sorbent assay (ELISA) and high-performance liquid chromatography/tandem mass spectroscopy. The BTx ozonolysis rate constant measured by ELISA was 5.74 ± 0.21 × 103 M-1 s-1. The corresponding lifetime for decay of 87.5% BTx in the presence of 20 ppb of O3 was 7.08 ± 0.26 h, suggesting that aerosolized BTx can still travel long distances at night before SSA deposition. BTx concentrations in SSA decreased more rapidly in the presence of sunlight than in its absence due to oxidation with photochemically produced OH radicals.

A reusable QCR aptasensor for the detection of Brevetoxin-2 in shellfish

Brevetoxins (BTX) are pharmacologically active, lipid soluble cyclic polyether neurotoxins that are known to cause a wide range of neurological symptoms in humans.Harvesting and consumption of infected molluscs provide an entry point for BTXs into, the food chain, causing long-term health effects on accumulation for individuals, commonly in people with a compromised immune system and existing allergies. This study is an acoustic assay that has been constructed using a 9 MHz AT-cut quartz crystal resonator modified by attaching a specific single-stranded DNA aptamer. The DNA oligo modifies its conformation to attach itself to the binding site of the incoming BTX molecule resulting in a change in frequency on the QCR. A small Δf value was observed for lower concentrations of BTX indicating a small change in mass deposited on the crystal surface, while the opposite was true for higher concentrations. Cross-species behavior was evaluated using samples of similar origin, molecular weight and a combination of two toxins. The LOD of the fabricated QCR is 220 nM which is lower than the maximum recommended residue limit in food samples. Fresh mussel samples were spiked with known concentrations of BTX to evaluate its sensitivity in a food matrix. No interaction with other compounds was observed. Overall, this sensor finds potential application in the food sector (fishing units) where mussels are tested and graded for allergens and toxins before reaching the customer.

Profiling of Brevetoxin Metabolites Produced by Karenia brevis 165 Based on Liquid Chromatography-Mass Spectrometry.

In this study, Karenia brevis 165 (K. brevis 165), a Chinese strain, was used to research brevetoxin (BTX) metabolites. The sample pretreatment method for the enrichment of BTX metabolites in an algal culture medium was improved here. The method for screening and identifying intracellular and extracellular BTX metabolites was established based on liquid chromatography-time-of-flight mass spectrometry (LC-ToF-MS) and liquid chromatography triple quadrupole tandem mass spectrometry (LC-QqQ-MS/MS). The results show that the recovery rates for BTX toxins enriched by a hydrophilic–lipophilic balance (HLB) extraction column were higher than those with a C18 extraction column. This method was used to analyze the profiles of extracellular and intracellular BTX metabolites at different growth stages of K. brevis 165. This is the first time a Chinese strain of K. brevis has been reported that can produce toxic BTX metabolites. Five and eight kinds of BTX toxin metabolites were detected in the cell and culture media of K. brevis 165, respectively. Brevenal, a toxic BTX metabolite antagonist, was found for the first time in the culture media. The toxic BTX metabolites and brevenal in the K. brevis 165 cell and culture media were found to be fully proven in terms of the necessity of establishing a method for screening and identifying toxic BTX metabolites. The results found by qualitatively and quantitatively analyzing BTX metabolites produced by K. brevis 165 at different growth stages show that the total toxic BTX metabolite contents in single cells ranged between 6.78 and 21.53 pg/cell, and the total toxin concentration in culture media ranged between 10.27 and 449.11 μg/L. There were significant differences in the types and contents of toxic BTX metabolites with varying growth stages. Therefore, when harmful algal blooms occur, the accurate determination of BTX metabolite types and concentrations will be helpful to assess the ecological disaster risk in order to avoid hazards and provide appropriate disaster warnings.

Comparison of during-bloom and inter-bloom brevetoxin and saxitoxin concentrations in Indian River Lagoon bottlenose dolphins, 2002–2011

Harmful algal bloom (HAB) toxins have severe negative impacts on marine mammals, particularly for Florida bottlenose dolphins (Tursiops truncatus) which frequently experience mass mortality events. Dolphins on the Florida Atlantic coast inhabit a region endemic to two HAB species, Karenia brevis and Pyrodinium bahamense, which produce the neurotoxins brevetoxin (PbTx) and saxitoxin (STX), respectively. Although toxic HABs and associated dolphin mortality events have been reported from this region, there is a lack of available data necessary for comparing toxin exposure levels between bloom (‘exposed’) conditions and non-bloom (‘baseline’) conditions. Here we present a 10-year dataset of PbTx and STX concentrations detected in dolphins stranding in this region, and compare the toxin loads from HAB-exposed dolphins to those detected in dolphins recovered in the absence of a HAB. We analyzed liver tissue samples from dead-stranded dolphins (n = 119) recovered and necropsied between 2002–2011, using an enzyme-linked immunosorbent assay (ELISA) modified for use with mammalian tissues. For dolphins recovered during baseline conditions, toxin-positive samples ranged in concentration from 0.27 to 1.2 ng/g for PbTx and from 0.41 to 1.9 ng/g for STX. For K. brevis-exposed dolphins, concentrations of up to 12.1 ng PbTx/g were detected, and for P. bahamense-exposed dolphins, concentrations of up to 9.9 ng STX/g were detected. Baseline PbTx values were similar to those reported in other regions where K. brevis blooms are more frequent and severe, but HAB-exposed PbTx values were considerably lower relative to these other regions. Since no baseline STX dolphin data exist for any region, our data serve as a first step towards establishing reference STX values for potential dolphin mortality events associated with STX-producing blooms in the future. This study demonstrates that although HABs in eastern Florida are only infrequently associated with dolphin mortalities, the presence of toxins in these animals may pose significant health risks in this region.

Brevetoxin-Producing Spherical Cells Present in Karenia brevis Bloom: Evidence of Morphological Plasticity?

Spherical cells were detected in low salinity waters during a bloom of Karenia brevis in Alabama coastal waters. These balls resembled K. brevis in size and organelle appearance, contained similar concentration of brevetoxin, and occurred during ongoing K. brevis bloom. Based on the environmental conditions in which these cells were observed, we speculate that a rapid drop in salinity triggered the sphere formation in K. brevis. Brevetoxin concentrations were comparable between surface water samples containing typical and atypical cells ranging from 1 to 10 ng/mL brevetoxin-3 equivalents. Accurate identification and quantification of cell abundance in the water column is essential for routine monitoring of coastal waters, so misidentification of these spherical cells may result in significant underestimation of cell densities, and consequently, brevetoxin level. These potential discrepancies may negatively impact the quality of regulatory decisions and their impact on shellfish harvest area closures. We demonstrate that traditional monitoring based on microscopy alone is not sufficient for brevetoxin detection, and supporting toxin data is necessary to evaluate potential risk.

Assessing Karenia brevis red tide as a mortality factor of sea turtles in Florida, USA.

Data on Karenia brevis red tides (≥105 cells l-1) and on dead or debilitated (i.e. stranded) Kemp's ridleys Lepidochelys kempii, loggerheads Caretta caretta, green turtles Chelonia mydas, hawksbills Eretmochelys imbricata, and leatherbacks Dermochelys coriacea documented in Florida during 1986-2013 were evaluated to assess red tides as a sea turtle mortality factor. Unusually large numbers of stranded sea turtles were found coincident with red tides primarily along Florida's Gulf coast but also along a portion of Florida's Atlantic coast. These strandings were mainly adult and large immature loggerheads and Kemp's ridleys, and small immature green turtles and hawksbills. Unusually large numbers of stranded leatherbacks never coincided with red tide. For the 3 most common species, results of stranding data modeling, and of investigations that included determining brevetoxin concentrations in samples collected from stranded turtles, all indicated that red tides were associated with greater and more frequent increases in the numbers of stranded loggerheads and Kemp's ridleys than in the number of stranded green turtles. The mean annual number of stranded sea turtles attributed to K. brevis red tide was 80 (SE = 21.6, range = 2-338). Considering typical stranding probabilities, the overall mortality was probably 5-10 times greater. Red tide accounted for a substantial portion of all stranded loggerheads (7.1%) and Kemp's ridleys (17.7%), and a smaller portion of all stranded green turtles (1.6%). Even though K. brevis red tides occur naturally, the mortality they cause needs to be considered when managing these threatened and endangered species.

Potential effects of brevetoxins and toxic elements on various health variables in Kemp's ridley (Lepidochelys kempii) and green (Chelonia mydas) sea turtles after a red tide bloom event

Natural biotoxins and anthropogenic toxicants pose a significant risk to sea turtle health. Documented effects of contaminants include potential disease progression and adverse impacts on development, immune function, and survival in these imperiled species. The shallow seagrass habitats of Florida's northwest coast (Big Bend) serve as an important developmental habitat for Kemp's ridley (Lepidochelys kempii) and green (Chelonia mydas) sea turtles; however, few studies have been conducted in this area. Our objectives were (1) to evaluate plasma analytes (mass, minimum straight carapace length, body condition index [BCI], fibropapilloma tumor score, lysozyme, superoxide dismutase, reactive oxygen/nitrogen species, plasma protein electrophoresis, cholesterol, and total solids) in Kemp's ridleys and green turtles and their correlation to brevetoxins that were released from a red tide bloom event from July–October 2014 in the Gulf of Mexico near Florida's Big Bend, and (2) to analyze red blood cells in Kemp's ridleys and green turtles for toxic elements (arsenic, cadmium, lead, mercury, selenium, thallium) with correlation to the measured plasma analytes. Positive correlations were observed between brevetoxins and α2-globulins in Kemp's ridleys and α2- and γ-globulins in green turtles, indicating potential immunostimulation. Arsenic, cadmium, and lead positively correlated with superoxide dismutase in Kemp's ridleys, suggesting oxidative stress. Lead and mercury in green turtles negatively correlated with BCI, while mercury positively correlated with total tumor score of green turtles afflicted with fibropapillomatosis, suggesting a possible association with mercury and increased tumor growth. The total tumor score of green turtles positively correlated with total protein, total globulins, α2-globulins, and γ-globulins, further suggesting inflammation and immunomodulation as a result of fibropapillomatosis. Lastly, brevetoxin concentrations were positively related to tumor score, indicating potential tumor promotion by brevetoxin. These results signify that brevetoxins and toxic elements elicit various negative effects on sea turtle health, including immune function, oxidative stress, and possibly disease progression.

Maternal transfer and sublethal immune system effects of brevetoxin exposure in nesting loggerhead sea turtles (Caretta caretta) from western Florida

Blooms of Karenia brevis (also called red tides) occur almost annually in the Gulf of Mexico. The health effects of the neurotoxins (i.e., brevetoxins) produced by this toxic dinoflagellate on marine turtles are poorly understood. Florida’s Gulf Coast represents an important foraging and nesting area for a number of marine turtle species. Most studies investigating brevetoxin exposure in marine turtles thus far focus on dead and/or stranded individuals and rarely examine the effects in apparently “healthy” free-ranging individuals. From May–July 2014, one year after the last red tide bloom, we collected blood from nesting loggerhead sea turtles (Caretta caretta) on Casey Key, Florida USA. These organisms show both strong nesting and foraging site fidelity. The plasma was analyzed for brevetoxin concentrations in addition to a number of health and immune-related parameters in an effort to establish sublethal effects of this toxin. Lastly, from July–September 2014, we collected unhatched eggs and liver and yolk sacs from dead-in-nest hatchlings from nests laid by the sampled females and tested these samples for brevetoxin concentrations to determine maternal transfer and effects on reproductive success. Using a competitive enzyme-linked immunosorbent assay (ELISA), all plasma samples from nesting females tested positive for brevetoxin (reported as ng brevetoxin-3[PbTx-3] equivalents [eq]/mL) exposure (2.1–26.7ng PbTx-3eq/mL). Additionally, 100% of livers (1.4–13.3ng PbTx-3eq/mL) and yolk sacs (1.7–6.6ng PbTx-3eq/mL) from dead-in-nest hatchlings and 70% of eggs (<1.0–24.4ng PbTx-3eq/mL) tested positive for brevetoxin exposure with the ELISA. We found that plasma brevetoxin concentrations determined by an ELISA in nesting females positively correlated with gamma-globulins, indicating a potential for immunomodulation as a result of brevetoxin exposure. While the sample sizes were small, we also found that plasma brevetoxin concentrations determined by an ELISA in nesting females significantly correlated with liver brevetoxin concentrations of dead-in-nest hatchlings and that brevetoxins could be related to a decreased reproductive success in this species. This study suggests that brevetoxins can still elicit negative effects on marine life long after a bloom has dissipated. These results improve our understanding of maternal transfer and sublethal effects of brevetoxin exposure in marine turtles.

Sublethal red tide toxin exposure in free-ranging manatees (Trichechus manatus) affects the immune system through reduced lymphocyte proliferation responses, inflammation, and oxidative stress

The health of many Florida manatees (Trichechus manatus latirostris) is adversely affected by exposure to blooms of the toxic dinoflagellate, Karenia brevis. K. brevis blooms are common in manatee habitats of Florida’s southwestern coast and produce a group of cyclic polyether toxins collectively referred to as red tide toxins, or brevetoxins. Although a large number of manatees exposed to significant levels of red tide toxins die, several manatees are rescued from sublethal exposure and are successfully treated and returned to the wild. Sublethal brevetoxin exposure may potentially impact the manatee immune system. Lymphocyte proliferative responses and a suite of immune function parameters in the plasma were used to evaluate effects of brevetoxin exposure on health of manatees rescued from natural exposure to red tide toxins in their habitat. Blood samples were collected from rescued manatees at Lowry Park Zoo in Tampa, FL and from healthy, unexposed manatees in Crystal River, FL. Peripheral blood leukocytes (PBL) isolated from whole blood were stimulated with T-cell mitogens, ConA and PHA. A suite of plasma parameters, including plasma protein electrophoresis profiles, lysozyme activity, superoxide dismutase (SOD) activity, and reactive oxygen/nitrogen (ROS/RNS) species, was also used to assess manatee health. Significant decreases (p<0.05) in lymphocyte proliferation were observed in ConA and PHA stimulated lymphocytes from rescued animals compared to non-exposed animals. Significant correlations were observed between oxidative stress markers (SOD, ROS/RNS) and plasma brevetoxin concentrations. Sublethal exposure to brevetoxins in the wild impacts some immune function components, and thus, overall health, in the Florida manatee.

Brevetoxin exposure, superoxide dismutase activity and plasma protein electrophoretic profiles in wild-caught Kemp's ridley sea turtles (Lepidochelys kempii) in southwest Florida

Because of their vulnerable population status, assessing exposure levels and impacts of toxins on the health status of Gulf of Mexico marine turtle populations is critical. From 2011 to 2013, two large blooms of the red tide dinoflagellate, Karenia brevis, occurred along the west coast of Florida USA (from October 2011 to January 2012 and October 2012 to April 2013). Other than recovery of stranded individuals, it is unknown how harmful algal blooms affected the Kemp's ridley sea turtles (Lepidochelys kempii) inhabiting the affected coastal waters. It is essential to gather information regarding brevetoxin exposure in these turtles to determine if it poses a threat to marine turtle health and survival. From April 2012 to May 2013, we collected blood from 13 immature Kemp's ridley turtles captured in the Pine Island Sound region of the Charlotte Harbor estuary. Nine turtles were sampled immediately after or during the red tide events (bloom group) while four turtles were sampled between the events (non-bloom group). Plasma was analyzed for total brevetoxins (reported as ng PbTx-3eq/mL), superoxide dismutase (SOD) activity, total protein concentration and protein electrophoretic profiles (albumin, alpha-, beta- and gamma-globulins). Brevetoxin concentrations ranged from 7.0 to 33.8ng PbTx-3eq/mL. Plasma brevetoxin concentrations in the nine turtles sampled during or immediately after the red tide events were significantly higher (by 59%, P=0.04) than turtles sampled between events. No significant correlations were observed between plasma brevetoxin concentrations and plasma proteins or SOD activity, most likely due to the small sample size; however alpha-globulins tended to increase with increasing brevetoxin concentrations in the bloom group. Smaller (carapace length and mass) bloom turtles had higher plasma brevetoxin concentrations than larger bloom turtles, possibly due to a growth dilution effect with increasing size. The research presented here improves the current understanding of potential impacts of environmental brevetoxin exposure on marine turtle health and survival.

Reponses of the dinoflagellate Karenia brevis to climate change: pCO2 and sea surface temperatures

Increasing atmospheric CO2 is promoting ocean acidification and higher global temperatures and has been suggested as a possible factor for shifts in marine phytoplankton composition to more harmful species. Karenia brevis is the major harmful algal species in the Gulf of Mexico producing potent neurotoxins known as brevetoxins. We examined how changes in ocean inorganic carbon chemistry associated with pre-industrial (250ppm), recent (350ppm), and predicted at 2100 (1000ppm) pCO2 levels and increased temperature affect growth rates and brevetoxin production in K. brevis. At the predicted pCO2 levels for 2100, growth rate of K. brevis Wilson clone increased substantially by 46% at 25°C (0.43±0.01d−1) compared to recent and pre-industrial levels (0.29±0.01d−1). Growth rates also increased for a low brevetoxin-producing clone, SP1, from 0.24±0.02d−1 at lower pCO2 levels to 0.33±0.003d−1 at a pCO2 of 1000ppm. When grown at a higher temperature (30°C), growth rates for the Wilson clone significantly decreased at all three pCO2 by approximately 30%. However, even at the higher temperature, K. brevis growth rate significantly increased by 30% (0.30±0.01d−1) at the 1000ppm CO2 level when compared to recent and pre-industrial CO2 levels (0.21±0.01d−1). Although K. brevis growth rate decreased at higher temperatures, the growth rate at pCO2 level of 1000 and 30°C was slightly higher than at current conditions (pCO2 level of 350 and 25°C). Modification of pCO2 levels and temperatures did not have an effect on total brevetoxin production or brevetoxin profiles in either clone examined. Due to the increased growth rate, total brevetoxin production was significantly higher at the pCO2 level of 1000. Finally, from these results we conclude there is no connection between growth rate and brevetoxin per cell. Although neither pCO2 nor temperature influenced brevetoxin production per cell, we suggest that under predicted future climate conditions K. brevis blooms have the potential to produce higher cell concentrations and increased brevetoxin concentrations, which will pose an increased risk for ecosystem and human health.

Bacteriocidal effects of brevetoxin on natural microbial communities

The sensitivity of bacteria to the marine neurotoxins, brevetoxins, produced by the dinoflagellate Karenia brevis and raphidophytes Chattonella spp. remains an open question. We investigated the bacteriocidal effects of brevetoxin (PbTx-2) on the abundance and community composition of natural microbial communities by adding it to microbes from three coastal marine locations that have varying degrees of historical brevetoxin exposure: (1) Great Bay, New Jersey, (2) Rehoboth Bay, Delaware and (3) Sarasota Bay, Florida. The populations with limited or no documented exposure were more susceptible to the effects of PbTx-2 than the Gulf of Mexico populations which are frequently exposed to brevetoxins. The community with no prior documented exposure to brevetoxins showed significant (p=0.03) changes in bacterial abundance occurring with additions greater than 2.5μgPbTx-2L−1. Brevetoxin concentrations during K. brevis blooms range from ∼2.5 to nearly 100μgL−1 with typical concentrations of ∼10–30μgL−1. In contrast to the unexposed populations, there was no significant decrease in bacterial cell number for the microbial community that was frequently exposed to brevetoxins, which implies variable sensitivity in natural communities. The diversity in the bacterial communities that were sensitive to PbTx-2 declined upon exposure. This suggests that the PbTx-2 was selecting for or against specific species. Mortality was much higher in the 200μgPbTx-2L−1 treatment after 48h and >37% of the species disappeared in the bacterial communities with no documented exposure. These results suggest that toxic red tides may play a role in structuring bacterial communities.

BREVETOXICOSIS IN SEABIRDS NATURALLY EXPOSED TO KARENIA BREVIS BLOOMS ALONG THE CENTRAL WEST COAST OF FLORIDA

Harmful algal bloom events caused by the dinoflagellate Karenia brevis occurred along the central west Florida, USA, coast from February 2005 through December 2005 and from August 2006 through December 2006. During these events, from 4 February 2005 through 28 November 2006, live, debilitated seabirds admitted for rehabilitation showed clinical signs that included disorientation, inability to stand, ataxia, and seizures. Testing of blood, biologic fluids, and tissues for brevetoxin by enzyme-linked immunosorbent assay found toxin present in 69% (n=95) of rehabilitating seabirds. Twelve of the 19 species of birds had evidence of brevetoxin exposure. Commonly affected species included Double-crested Cormorants (Phalacrocorax auritus), Brown Pelicans (Pelecanus occidentalis), Great Blue Herons (Ardea herodias), and Common Loons (Gavia immer). Serial blood and fecal samples taken from several live seabirds during rehabilitation showed that brevetoxin was cleared within 5-10 days after being admitted to the rehabilitation facility, depending on the species tested. Among seabirds that died or were euthanized, the highest brevetoxin concentrations were found in bile, stomach contents, and liver. Most dead birds had no significant pathologic findings at necropsy, thereby supporting brevetoxin-related mortality.

Bioaccumulation and depuration of brevetoxins in the eastern oyster (Crassostrea virginica) and the northern quahog (= hard clam, Mercenaria mercenaria)

The eastern oyster (Crassostrea virginica) and northern quahog (= hard clam, Mercenaria mercenaria) are two species of economic and ecological significance in east coast waters of the United States and the Gulf of Mexico. Commercial industries for these species, especially within the state of Florida, are significant. The current study was undertaken to build upon the already established body of knowledge surrounding effects of the toxic dinoflagellate Karenia brevis on shellfish, to provide an understanding of the kinetics of brevetoxins within shellfish tissues, and to provide an estimate of brevetoxin retention times in these shellfish after a bloom event.Individual clams and oysters were exposed to the toxic dinoflagellate, K. brevis at a bloom concentration of 5 × 105 cells·L−1 for eight days and then transferred to filtered water for depuration. Individuals were sampled periodically to determine depuration rates. Concentrations of brevetoxins (and/or their metabolites measured as PbTx-3 equivalent) in tissues were determined using an Enzyme Linked Immunosorbent Assay (ELISA). After five days of exposure, brevetoxin levels in tissues of both species reached concentrations well above the regulatory limit of 800 ng g−1 (Pb-TX3 equivalent). Averaged concentration of brevetoxins in clams was 1000 ng g−1, while the oysters averaged 1986 ng g−1. After two weeks of depuration, tissue concentrations in both species were below regulatory levels with clams averaging ∼204 ng g−1 and oysters averaging ∼437 ng g−1. Toxins (or their metabolities) remained detectable in both clams (139 days) and oysters (82 days) for the duration of the experiment.

NITROGEN LIMITATION INCREASES BREVETOXINS IN KARENIA BREVIS (DINOPHYCEAE): IMPLICATIONS FOR BLOOM TOXICITY(1).

Laboratory and field measurements of the toxin content in Karenia brevis cells vary by >4-fold. These differences have been largely attributed to genotypic variations in toxin production among strains. We hypothesized that nutrient limitation of growth rate is equally or more important in controlling the toxicity of K. brevis, as has been documented for other toxic algae. To test this hypothesis, we measured cellular growth rate, chlorophyll a, cellular carbon and nitrogen, cell volume, and brevetoxins in four strains of K. brevis grown in nutrient-replete and nitrogen (N)-limited semi-continuous cultures. N-limitation resulted in reductions of chlorophyll a, growth rate, volume per cell and nirtogen:carbon (N:C) ratios as well as a two-fold increase (1%-4% to 5%-9%) in the percentage of cellular carbon present as brevetoxins. The increase in cellular brevetoxin concentrations was consistent among genetically distinct strains. Normalizing brevetoxins to cellular volume instead of per cell eliminated much of the commonly reported toxin variability among strains. These results suggest that genetically linked differences in cellular volume may affect the toxin content of K. brevis cells as much or more than innate genotypic differences in cellular toxin content per unit of biomass. Our data suggest at least some of the >4-fold difference in toxicity per cell reported from field studies can be explained by limitation by nitrogen or other nutrients and by differences in cell size. The observed increase in brevetoxins in nitrogen limited cells is consistent with the carbon:nutrient balance hypothesis for increases in toxins and other plant defenses under nutrient limitation.

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.