Image of large cell Pseudo-nitzschia by Brian Bill, NOAA Image of small cell Pseudo-nitzschia by Brian Bill, NOAA
Left image: Large size cells of Pseudo-nitzschia; Right image: Small size cells of Pseudo-nitzschia
Photo credit: Brian Bill, NOAA

Phytoplankton of the month — July 2015

Pseudo-nitzschia spp.

Pseudo-nitzschia spp. are pennate diatoms. For the purposes of SoundToxins, we categorize them into two size classes: Large size cells (P. australis, P. heimii, P. fraudulenta, P. pungens, P. multiseries) which are generally 50-145 µm long and 2.5-10.0 µm wide and small size cells (P. pseudodelicatissima, P. delicatissima, P. cuspidata) which are generally 30 to 90 µm long and 1.0-2.0 µm wide.

The genus Pseudo-ntizschia includes approximately eight species that SoundToxins is looking for, including P. australis, P. multiseries, P. heimii, P. fraudulenta, P. pungens, P. pseudodelicatissima, P. delicatissima, and P. cuspidata.

This genus is known to produce domoic acid, a naturally occurring toxin. Domoic acid can be accumulated by both shellfish and finfish. Organisms can accumulate domoic acid without apparent ill effects; however, in humans the toxin interferes with nerve signal transmission. Also known as Amnesic Shellfish Poisoning (ASP), mild domoic acid poisoning symptoms can include nausea, vomiting, dizziness, and possibly short-term memory loss, while people poisoned with very high doses of the toxin can die.

Domoic acid poisoning via shellfish was first observed in Eastern Canada when three people died and 105 people became ill from eating contaminated blue mussels from Prince Edward Island in 1987. The toxin has since been identified along the West coast in fish and shellfish causing the closures of both recreational and commercial fisheries for extended periods of time. These closures have had serious economic impacts on the communities dependent on these fisheries.

The Washington Department of Health actively monitors and routinely closes shellfish harvesting areas when domoic acid levels are at or above 20 ppm, except in the viscera of Dungeness crab where the closure level is 30 ppm. SoundToxins volunteers identify and count Pseudo-ntizschia cells from whole water samples and provide an alert when the large size varieties are observed at cell counts over 50,000 cells/L and small size varieties are at cell counts over 1,000,000 cells/L.

For more information about Domoic Acid Poisoning, please refer to NOAA's Harmful Algal Blooms and Biotoxins page.

For more information on Pseudo-nitzschia see the following references:

A Taxonomic Guide to Some Common Marine Phytoplankton, by Rita Horner (Biopress Ltd. 2002)

Fryxell, G.A., M.C. Villac, and L.P. Shapiro. 1997. The occurrence of the toxic diatom genus Pseudo-nitzschia (Bacillariophyceae) on the West Coast of the USA, 1920-1996: a review. Phycologia 36:419-437

Hasle, G.R. and E.E. Syvertsen. 1996. Marine Diatoms, pp.5-385. In: C.R. Tomas (ed.) Identifying Marine Diatoms and Dinoflagellates, Academic Press, San Diego.

Hasle, G.R., C.B. Lange, and E.E. Syvertsen. 1996. A review of Pseudo-nitzschia, with special reference to the Skagerrak, North Atlantic, and adjacent waters. Helgolander Meeresunters. 50:131-175

Skov, J., N. Lundholm, O. Moestrop, and J. Larsen. 1999. Potentially toxic phytoplankton 4. The diatom genus Pseudo-nitzschia (Diatomophyceae/Bacillariophyceae). ICES Identificatioin Leaflets for Plankton. Leaflet No. 185. ICES, Copenhagen. 23 pp.

Lundholm, N. et al. 2003. A study of the Pseudo-nitzschia pseudodelicatissima/cuspidata complex (Bacillariophyceae): What is P. pseudodelicatissima? J. Phycol. 39:797-813

Lundholm, N. et al. 2006. Inter- and intraspecific variation of the Pseudo-nitzschia delicatissima complex (Bacillariophyceae) illustrated by rRNA probes, morphological data and phylogenetic analyses. J. Phycol. 42:464-481

Lundholm, N. et al. 2010. Cryptic and pseudo-cryptic diveristy among species of the diatom genus Pseudo-nitzschia based on nuclear, plastid and mitochondrial sequence data; including descriptions of P. hasleana sp. nov. and P. fryxelliana sp. nov.

SoundToxins, a diverse partnership of Washington state shellfish and finfish growers, environmental learning centers, Native American tribes, and Puget Sound volunteers, is a monitoring program designed to provide early warning of harmful algal bloom events in order to minimize both human health risks and economic losses to Puget Sound fisheries.

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