In March 2025, a harmful algal bloom began spreading through the coastal waters of South Australia’s Gulf St Vincent and Spencer Gulf. By early 2026, it was still ongoing — one of the longest-running marine HAB events on record in the Southern Hemisphere. The organism responsible was Karenia mikimotoi, a dinoflagellate species that had never before been detected in Australian waters. It killed thousands of marine creatures across hundreds of kilometers of coastline. Beachgoers reported coughing, eye irritation, and blurred vision from aerosolized toxins. And it left aquaculture operators, fisheries agencies, and food safety labs confronting an uncomfortable question: if a bloom species previously unknown to an entire continent can appear and persist for over a year, how confident are you in the geographic assumptions behind your shellfish toxin testing program?

For decades, shellfish toxin monitoring has been organized around predictable geographic risk. Brevetoxins and Neurotoxic Shellfish Poisoning (NSP) were a Gulf of Mexico concern. Paralytic Shellfish Poisoning (PSP) from saxitoxin was a New England red tide problem, a Pacific Northwest concern, a North Sea issue. Diarrhetic Shellfish Poisoning (DSP) from okadaic acid was tracked closely in European and Asian coastal waters. Monitoring programs built around these regional patterns made practical sense when HAB-causing species stayed largely within their known distributions.

That organizing principle is breaking down. Rising sea surface temperatures, shifting ocean circulation patterns, and the documented range expansion of HAB-causing dinoflagellates mean that toxin syndromes once confined to specific coastlines are appearing in waters where they have no historical precedent. The South Australian Karenia mikimotoi bloom is one of the most striking examples in recent memory, but it is far from isolated. Alexandrium species producing saxitoxin have expanded their northern and southern range limits in the Atlantic. Dinophysis, which produces okadaic acid and drives DSP events, has appeared in shellfish harvesting areas that previously had no history of DSP closure. The practical implication for shellfish safety testing is significant: monitoring programs built around local historical risk may no longer reflect the actual hazard profile of the waters they protect.

Shellfish toxicity from harmful algal blooms is not a single clinical or analytical problem — it is four distinct ones, each driven by different toxin classes, different causative organisms, and different regulatory action levels. A robust shellfish safety program needs tools that address all four. Understanding the distinctions between them is the starting point for building a testing panel that closes the gaps rather than just checking regulatory boxes.

Brevetoxins are cyclic polyether neurotoxins produced primarily by Karenia brevis, the Florida red tide organism, and by related Karenia species including K. mikimotoi. They bind to voltage-gated sodium channels, causing neurological symptoms including tingling, numbness, dizziness, and in severe cases respiratory compromise. Unlike many other shellfish toxins, brevetoxins can also be aerosolized by wave action, causing respiratory irritation in beachgoers even without shellfish consumption — a feature that made the South Australian bloom events so alarming to coastal communities. Filter-feeding shellfish concentrate brevetoxins from the water column during bloom events, and because the toxins are highly stable (surviving heat up to 300°C), they cannot be eliminated from contaminated tissue by cooking. Brevetoxins are not toxic to the shellfish themselves, making visual inspection of harvested product useless as a safety screen. The only reliable path to consumer protection is analytical testing of shellfish tissue.

Attogene’s Brevetoxin ELISA Kit (SKU: EL2023-05) is a competitive immunoassay designed for regulatory-grade quantitative measurement of brevetoxins in shellfish tissue, water, and environmental samples. It has been validated for use in the sensitive matrices that shellfish toxin monitoring requires and is widely used by monitoring programs tracking red tide events in Gulf Coast shellfish harvesting areas. The CDC has also explored adapted versions of commercial brevetoxin ELISA methods for measuring human plasma exposure following bloom events — underscoring the clinical relevance of this detection platform beyond food safety alone.

Saxitoxin and its more than 30 analogues constitute the paralytic shellfish toxin (PST) family, produced primarily by marine dinoflagellates of the genus Alexandrium and by certain freshwater cyanobacteria. PSP is the most clinically dangerous of the shellfish toxin syndromes — saxitoxin LD50 values in rodents of 3–9 µg/kg intravenously place it among the most acutely toxic natural compounds known, and human fatalities from PSP have been recorded globally. Filter-feeding bivalves can accumulate sufficient toxin to cause human illness within 24 hours of filter feeding during an active bloom. Connecticut’s aquaculture monitoring program, established in 1985, documents how consistently PSP risk correlates with seasonal bloom dynamics — and how that window of risk is expanding as water temperatures warm earlier each year.

For rapid field screening of water and source water during bloom events, Attogene’s Saxitoxin Lateral Flow Kit for Freshwater (SKU: AU2057) detects saxitoxin at concentrations as low as 70 ppt with a 15-minute run time. For shellfish tissue screening, the Saxitoxin Shellfish Rapid Test (SKU: AU2057-01) provides 30-minute qualitative screening of extracts at the 50 ppb tissue threshold, allowing harvest area managers to make rapid closure decisions during bloom events without waiting for laboratory confirmation. Positive rapid test results can then be confirmed by ELISA or HPLC for regulatory reporting purposes.

Okadaic acid (OA), produced by dinoflagellate genera Dinophysis and Prorocentrum, is the principal causative toxin of Diarrhetic Shellfish Poisoning. DSP produces dose-dependent gastrointestinal illness — diarrhea, nausea, and vomiting — that is rarely fatal but has caused significant shellfish market disruptions in Europe, Japan, and increasingly in North American and South American coastal harvesting areas. The FDA action level for OA is 200 ppb in shellfish tissue; the EU standard is stricter at 160 ppb. Because DSP symptoms overlap with common foodborne illness, it is systematically underreported, and outbreaks are frequently attributed to other causes before shellfish testing identifies OA as the culprit.

Attogene offers both field-deployable and laboratory-grade DSP detection. The Okadaic Acid (DSP) Lateral Flow Kit (SKU: AU2071) provides rapid qualitative shellfish tissue screening, while the Okadaic Acid (DSP) ELISA Kit (SKU: EL2050-01) delivers quantitative results compatible with regulatory reporting for both FDA and EU action level requirements. The ELISA is compatible with the Nix Sensor and standard plate readers for quantitative output. These tools allow programs to implement the same two-tier field-screening-plus-lab-confirmation workflow that is now standard practice for PSP monitoring.

One of the most significant limitations of conventional shellfish toxin monitoring is its reactive nature. Grab samples from shellfish tissue or seawater capture a single point in time and may miss episodic toxin events entirely, particularly for toxins like okadaic acid and brevetoxin that appear in water at concentrations too low for standard grab sample methods to reliably detect before shellfish accumulation has already occurred. Passive sampling changes this dynamic by continuously concentrating dissolved toxins from the water column over deployment periods of days to weeks, providing an integrated signal that reflects real exposure rather than a single moment.

Attogene’s Solid Phase Adsorption Toxin Tracking (SPATT) Bag Set (SKU: CO2029) uses HP20 resin to passively capture an exceptionally broad range of marine and freshwater toxins from a single deployment — including brevetoxins, saxitoxin and PST analogues, okadaic acid and DSP toxins, cyclic imines such as spirolides and gymnodimines, ciguatoxin precursors, domoic acid, and yessotoxins. This makes SPATT an ideal sentinel technology for coastal shellfish harvesting areas facing expanding or unpredictable bloom risk — the kind of geographic uncertainty that the South Australian bloom event has placed front of mind for monitoring programs globally. SPATT devices also provide superior recovery for toxins that are systematically underrepresented in conventional grab samples, including microcystin-LR and cylindrospermopsin in freshwater environments adjacent to estuarine shellfish beds.

The South Australia bloom is a useful forcing function for any shellfish safety program conducting a gap analysis of its current testing panel. The questions to ask are straightforward: Does your program screen for the full range of marine shellfish toxin syndromes — NSP, PSP, and DSP — or only the ones with historical local precedent? Do you have both rapid field screening and quantitative laboratory confirmation capabilities for each? Do you have a passive sentinel monitoring component that can catch toxin accumulation events before shellfish tissue reaches actionable concentrations? And is your program equipped to detect the next novel species before the outbreak, or only to confirm it after?

Attogene’s shellfish toxin detection portfolio is built around exactly this kind of complete panel approach — rapid lateral flow screening for PSP and DSP, ELISA-based quantification for brevetoxin and okadaic acid, and SPATT passive sampling technology for broad-spectrum sentinel monitoring across marine, estuarine, and freshwater matrices. Browse the full range of tools at the Attogene product list, or reach out to the team to design a testing protocol matched to your harvest area geography, regulatory requirements, and bloom risk profile.

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The Attogene SPATT Bag Set uses HP20 resin with broad-spectrum capture capability covering brevetoxins, saxitoxin and paralytic shellfish toxin (PST) analogues, okadaic acid and DSP toxins (dinophysistoxins), cyclic imines including spirolides, gymnodimines, and pinnatoxins, domoic acid, yessotoxins, ciguatoxin precursors, microcystin, cylindrospermopsin, nodularin, and anatoxin-a. This makes it one of the most analytically comprehensive passive sampling options available for coastal and inland water monitoring programs.

No. Brevetoxins are extraordinarily heat-stable, remaining biologically active after exposure to temperatures exceeding 300°C. Cooking, boiling, steaming, or freezing contaminated shellfish does not render them safe. This is a critical public health message for communities near red tide events, and it is the reason that ELISA-based testing of shellfish tissue — not processing or preparation controls — is the only reliable intervention between a contaminated harvest and consumer harm.

The U.S. regulatory action level for paralytic shellfish toxins (saxitoxin equivalents) in shellfish tissue is 80 µg STX equivalents per 100 grams of shellfish meat, as established under the National Shellfish Sanitation Program. The EFSA (European Food Safety Authority) recommended an action level of 0.6 ppb for saxitoxin in source water. Attogene’s Saxitoxin Shellfish Rapid Test detects saxitoxin at or above 50 ppb in tissue extracts, providing a screening margin below the regulatory threshold.

Grab sampling captures toxin concentrations at a single point in time, which can miss episodic bloom events or underestimate toxin accumulation for compounds present at low dissolved concentrations. SPATT passive samplers are deployed in the water column for days to weeks and continuously concentrate dissolved toxins onto a resin matrix, providing an integrated time-averaged signal that better reflects actual exposure. SPATT technology has been shown to detect toxins like microcystin-LR and cylindrospermopsin at lower effective concentrations than grab sampling, and provides better representation of episodic toxin pulses that grab samples taken between events would miss entirely.