Red tides and toxic algal bloomswho's to blame?

Resumen

Nigh on 5000 living phytoplankton species that make up the base of the marine food web. only 40 are known to be toxic. However, some dinoflagellates are able to produce such potent toxins that just a few dozen of cells per litre can be very harmful, While harmful algal blooms are natural phenomena that have occurred throughout recorded history, there is a conviction among many experts that the scale and complexity of this natural phenomenon are expanding. So. a major constraint to research and monitoring programmes for harmful algae stems from the need to identify the toxin-producing species within a mixed plankton sample. Invariably. microalgae maintain a fixed morphology whilst accumulating genetic variability within them. Hence, while considerable time, effort and skill are required to identify the alga responsible using microscopy, misidentification may appear if morphology is the sole criterion for the identification of toxin-producing species. A working alternative to morphological identification is the use of molecular probes that can bind to species-specific sites on thin target cells, to be visualized using spectrofluorirnetry, flow-cytornetry or epifluorescent microscopy. This communication will outline the recent progress in rooting out the dinoflagellates responsible for red tides and toxic algal blooms. The development of immunological, lectin-based and nucleic acid-based probes for harmful algal species goes hand in hand with this search. One such example of misplaced blame is the Mediterranean red-tide but non-toxic dinoflagellate Gyrodinium impudicurn. It is so morphologically similar to the PSP toxin-producing Gymnodinium catenatum that neither species can be distinguished in forrnalin-fixed samples. Regular misidentification of these species has been long suspected. However both species can be rapidly and easily differentiated using the FITC-labelled WA lectini which specifically binds to G. catenaturn. Thus the blame can be shifted back to the toxic species. Molecular probes can also clarify the taxonomy of toxigenic genera, for example, the genus Alexancirium. Further uses include facilitating rapid cell counts and separating toxic species, e.g. A. minutum, from mixed plankton assemblages from nature which can further aid the apparently unending search for the guilty algal species.