Overview and present status of the toxic Pfiesteria complex (Dinophyceae)

Abstract

This paper reviews the Pfiesteria issue and Pfiesteria science and presents new information on variation in toxicity among Pfiesteria strains, culture effects on their toxicity, the trophic interactions of Pfiesteria spp ., and impacts on fish and mammals. We also assess Pfiesteria spp. impacts on fish in comparison to certain other estuarine dinoflagellates of similar appearance. Species of the toxic Pfiesteria complex (TPC) thus far include P. piscicida and P. shumwayae. These species share morphological and genetic similarities, and both have toxic strains that (1) show strong attraction to live fish;(2) exhibit toxicity that is triggered by live fish or their fresh tissues and excreta; and (3) produce toxin(s) that cause fish stress, disease and death under ecologically relevant conditions (the standardized fish bioassay process involves testing live Pfiesteria cells at similar densities to those encountered during Pfiesteria-related fish kill/disease events). Both Pfiesteria species also have a complex life cycle with multiple amoeboid, flagellated and cyst stages, several of which are ichthyotoxic. TPC species are eurythermal and euryhaline, with prey spanning the estuarine food web, from bacteria to mammalian tissues. They can be stimulated directly or indirectly by nitrogen and phosphorus enrichment. Toxic strains can be either actively or potentially toxic (the TOX-A and TOX-B functional types, respectively); in addition, c.40% of randomly isolated clones have been found to be benign [the noninducible or NON-IND functional type, which apparently lacks the ability to produce bioactive substances (toxins) that cause fish disease or death]. These functional types differ significantly in response to algal prey, predators, nutrients and fish. Moreover, as an apparent artifact of culture conditions, toxic strains generally lose their ability to cause fish death and disease and become NON-IND within weeks to months. At low cell densities, toxic strains can be causative agents of acute and/or chronic diffuse and focal lesions and of other fish diseases, as demonstrated in fish bioassays. A partially purified, water-soluble Pjiesteria toxin disrupts calcium metabolism in rat pituitary cells and mimics an adenosine triphosphate neurotransmitter that targets P2X7 purinoreceptors found predominantly on immune cells. Respiratory, visual, and neurological impacts have been sustained by people exposed to aerosols from fish-killing Pfiesteria cultures or to water and aerosols during estuarine fish kills associated with toxic Pfiesteria. Neurocognitive impacts from exposure to toxic Pfiesteria have been replicated experimentally in small mammals. Toxic strains of Pfiesteria species have been confirmed from mid-Atlantic and Gulf Coast estuaries in the United States and from northern Europe and New Zealand, indicating that these toxic dinoflagellates are cosmopolitan in distribution.