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VICTORIA LÓPEZ-RODAS Y COLS. AN. R. ACAD. NAC. FARM.

addition, some species are so toxic that they can produce serious
problems occurring at such a low density that they are virtually
invisible to cell counts in monitoring programs. Considerable time
and effort are required to identify a particular species especially
when its distinguishing characteristics are difficult to discern under
light microscopy (5).

Invariably, microalgae maintain a fixed morphology, whilst
accumulating genetic variability within them. Hence, while great
effort is required to identify and counting toxin-producing
microalgae using microscopy, misidentification may appear if
morphology is the unique criterion for the identification of toxin
producing species. A working alternative is the use of molecular
probes that can bind species-specific sites on target harmful algae,
to be visualized using flow-cytometry, spectrofluorometry, or
epifluorescence microscopy. The use of immunological (32-33),
lectin-based (34-35) and DNA based probes (36) for harmful algal
species identification is increasing in monitoring programs. These
cellular and molecular probes allow a precise identification that is
impossible using classic microscopic identification. As an example
of misidentification, the red tide non-toxic dinoflagellate Gyrodinium
impudicum was continuously confused with the PSP toxin-producing
dinoflagellate Gymnodinium catenatum. G. impudicum is so
morphologically similar to G. catenatum that both species cannot be
distinguished in formalin fixed samples. However, both species can
be easily differentiated using the WGA lectin, which specifically binds
to G. catenatum. Misidentification during decades between these
species originated enormous economic looses when shellfish yield
was forbidden after detect the innocuous species G. impudicum in
water samples (5).

Shellfish yield is forbidden when the toxins exceed the prescribed
limits providing a margin of safety to prevent contaminated shellfish
reach the market. In spite of regulation on DSP toxins are usually
taking into account, repeatedly outbreaks of DSP provoked by
ingestion of mussels have been reported in European countries (24,
37). Even recently, shellfish contained more than 0,16 µg/g of okadaic
acid have been detected in UE markets (25-26, 38). In addition, DSP
outbreaks are probably undervalued because DSP is a self-limited
and mild disease, and the most patients with DSP are detected when

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