a b s t r a c tParalytic shellfish poisoning (PSP) is the foodborne illness associated with the consumption of seafood products contaminated with the neurotoxins known collectively as saxitoxins (STXs). This family of neurotoxins binds to voltage-gated sodium channels, thereby attenuating action potentials by preventing the passage of sodium ions across the membrane. Symptoms include tingling, numbness, headaches, weakness and difficulty breathing. Medical treatment is to provide respiratory support, without which the prognosis can be fatal. To protect human health, seafood harvesting bans are in effect when toxins exceed a safe action level (typically 80 mg STX eq 100 g À1 tissue). Though worldwide fatalities have occurred, successful management and monitoring programs have minimized PSP cases and associated deaths. Much is known about the toxin sources, primarily certain dinoflagellate species, and there is extensive information on toxin transfer to traditional vectors -filter-feeding molluscan bivalves. Non-traditional vectors, such as puffer fish and lobster, may also pose a risk. Rapid and reliable detection methods are critical for toxin monitoring in a wide range of matrices, and these methods must be appropriately validated for regulatory purposes. This paper highlights PSP seafood safety concerns, documented human cases, applied detection methods as well as monitoring and management strategies for preventing PSP-contaminated seafood products from entering the food supply.Published by Elsevier Ltd. Paralytic shellfish poisoning toxins and sourcesParalytic shellfish poisoning (PSP) is a common seafood toxicity problem with worldwide distribution, and typically this illness is due to the consumption of contaminated molluscan bivalves and other shellfish. A similar seafood-related syndrome involves puffer fish contaminated with the same family of toxins. To distinguish these puffer fish poisonings from those caused by tetrodotoxin, this food poisoning syndrome is becoming known in the literature as saxitoxin puffer fish poisoning (SPFP; Landsberg et al., 2006;Deeds et al., 2008a). The toxins responsible for both of these seafood-borne illnesses are the neurotoxins known collectively as the saxitoxins (STXs), also referred to as PSP toxins (or PSTs). At least 24 saxitoxin-like congeners have been identified (Fig. 1), with a range of hydroxyl, carbamyl, and sulfate moieties at four sites on the backbone structure. These substitutions result in congeners varying more than three orders of magnitude in potency (Oshima et al., 1993). The carbamate toxins are the most potent, and they include saxitoxin (STX), neosaxitoxin (NEO), and the gonyautoxins (GTX1-4). The decarbamoyl toxins (dcSTX, dcNEO, dcGTX1-4) have intermediate toxicity and are reported in certain bivalves, but are not commonly found in toxic dinoflagellates. The N-sulfocarbamoyl toxins (B1 [GTX5], B2 [GTX6] and C1-4) are less potent. There is a fourth group known as the deoxydecarbamoyl toxins, but their potency has not yet *

BackgroundFrom January 2002 to May 2004, 28 puffer fish poisoning (PFP) cases in Florida, New Jersey, Virginia, and New York were linked to the Indian River Lagoon (IRL) in Florida. Saxitoxins (STXs) of unknown source were first identified in fillet remnants from a New Jersey PFP case in 2002.MethodsWe used the standard mouse bioassay (MBA), receptor binding assay (RBA), mouse neuroblastoma cytotoxicity assay (MNCA), Ridascreen ELISA, MIST Alert assay, HPLC, and liquid chromatography-mass spectrometry (LC-MS) to determine the presence of STX, decarbamoyl STX (dc-STX), and N-sulfocarbamoyl (B1) toxin in puffer fish tissues, clonal cultures, and natural bloom samples of Pyrodinium bahamense from the IRL.ResultsWe found STXs in 516 IRL southern (Sphoeroides nephelus), checkered (Sphoeroides testudineus), and bandtail (Sphoeroides spengleri) puffer fish. During 36 months of monitoring, we detected STXs in skin, muscle, and viscera, with concentrations up to 22,104 μg STX equivalents (eq)/100 g tissue (action level, 80 μg STX eq/100 g tissue) in ovaries. Puffer fish tissues, clonal cultures, and natural bloom samples of P. bahamense from the IRL tested toxic in the MBA, RBA, MNCA, Ridascreen ELISA, and MIST Alert assay and positive for STX, dc-STX, and B1 toxin by HPLC and LC-MS. Skin mucus of IRL southern puffer fish captive for 1-year was highly toxic compared to Florida Gulf coast puffer fish. Therefore, we confirm puffer fish to be a hazardous reservoir of STXs in Florida’s marine waters and implicate the dinoflagellate P. bahamense as the putative toxin source.ConclusionsAssociated with fatal paralytic shellfish poisoning (PSP) in the Pacific but not known to be toxic in the western Atlantic, P. bahamense is an emerging public health threat. We propose characterizing this food poisoning syndrome as saxitoxin puffer fish poisoning (SPFP) to distinguish it from PFP, which is traditionally associated with tetrodotoxin, and from PSP caused by STXs in shellfish.

Paralytic shellfish poisoning (PSP), due to saxitoxin and related compounds, typically results from the consumption of filter-feeding molluscan shellfish that concentrate toxins from marine dinoflagellates. In addition to these microalgal sources, saxitoxin and related compounds, referred to in this review as STXs, are also produced in freshwater cyanobacteria and have been associated with calcareous red macroalgae. STXs are transferred and bioaccumulate throughout aquatic food webs, and can be vectored to terrestrial biota, including humans. Fisheries closures and human intoxications due to STXs have been documented in several non-traditional (i.e. non-filter-feeding) vectors. These include, but are not limited to, marine gastropods, both carnivorous and grazing, crustacea, and fish that acquire STXs through toxin transfer. Often due to spatial, temporal, or a species disconnection from the primary source of STXs (bloom forming dinoflagellates), monitoring and management of such non-traditional PSP vectors has been challenging. A brief literature review is provided for filter feeding (traditional) and nonfilter feeding (non-traditional) vectors of STXs with specific reference to human effects. We include several case studies pertaining to management actions to prevent PSP, as well as food poisoning incidents from STX(s) accumulation in non-traditional PSP vectors.

A recently described unicellular chlorophytic alga isolated from meromictic Mono Lake, California, occupies a niche that spans two environments: the upper oxic mixolimnion and the deeper anoxic and highly reducing monimolimnion. This organism, Picocystis sp. strain ML, accounts for nearly 25% of the primary production during the winter bloom and more than 50% at other times of the year. In incubations, it is heavily grazed by the brine shrimp, Artemia monica. We assessed growth and photosynthetic parameters over broad ranges of irradiance, salinity, and pH and under oxic and anoxic conditions. Picocystis appears to be particularly adapted to low irradiance; we observed an order of magnitude increase in the cellular pigment concentrations, as well as marked increases in cellspecific photosynthetic parameters for cells acclimated to low-growth irradiance. Growth rates of 0.3-1.5 d Ϫ1 were observed over a salinity range of 0-260‰ and a pH range of 4-12, with maximal growth at ϳ50 mol photons m Ϫ2 s Ϫ1 , 40‰, and pH 6-10. Growth and oxygenic photosynthesis were observed under anoxic conditions at rates comparable to those measured under oxic conditions. The ability of the organism to acclimate and grow under such a broad range of environmental conditions makes it an important component of the Mono Lake ecosystem and likely contributes to its dominance of the monimolimnion/mixolimnion interface.Phototrophic microorganisms exhibit a remarkable capability for adaptation and acclimation that allows them to inhabit niches representing temporally varying biological extremes of light, salinity, pH, and water potential (Gorbushina and Krumbein 1999). In aquatic environments, phytoplankton undergo large increases in cellular pigment concentra-1 To whom correspondence should be addressed. Present address: Bigelow Laboratory for Ocean Sciences, West Boothbay Harbor, Maine 04575 (croesler@bigelow.org).2 Present address: District Office, USGS, Augusta, Maine 04330. AcknowledgmentsThe authors thank Jennifer Simeon for culturing assistance, Victor Paganelli (USGS Menlo Park) for processing the total dissolved inorganic carbon samples, and members of the Sierra Nevada Aquatic Research Laboratory for collecting water samples from Mono Lake. The University of Connecticut supported C.S.R. and S.M.E.; the USGS National Research Program supported C.W.C., L.G.M., and R.S.O.; and NSF supported R.P.K. (OCE-9907471).