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

In some cases the microalgal species of red tides produce toxins
that are deleterious to fauna. In other cases algal cells become so
dense during the red tides that they produce anoxic conditions. As
result red tides usually cause the death of thousands of marine
animals (invertebrates, fishes, birds…), including vertebrates as big
as monk seals and humpback whales (1-3).

Ancient proverbs and oral traditions of seaside peoples prevent
against red tides and HABs effects. As an example, a popular
tradition in NW of Spain warns people against eating mussels
towards the end of the summer. Thousands cases of human
poisoning by microalgal toxins (usually from shellfish consumption)
are reported each year in the first world (4-5). But only recently we
commence to understand how HABs, red tides, the marine ecosystem
integrity, global change and human health are intimately linked.

MICROALGAE, HABS, AND RED TIDES

Marine unicellular microscopic algae generate 40% of primary
production on the Earth (6-7). They form part of marine food chain
and make higher life possible in oceans and shores, and allow human
fisheries and aquaculture. Of the thousands of marine microalgae
species (˜ 70000) that occurs in the sea, only a small number are
harmful (8). Around a dozen produce red tides, and only 40 are
known to be toxic (9). Not all red tides are toxic, and not all toxic
microalgae produce red tides. When these species proliferate, they
can cause massive mortality among marine organisms (Figure 1),
damage marine cultures, fisheries, and human health (9-10). The
proliferation of toxic algae is denominated harmful algal blooms
(HAB). HAB may generate high densities of toxic population, but
low dense population (200 cells/l or less) of some toxic species can
be enough to cause poisoning (11).

DINOFLAGELLATES

The majority of the toxic and red tide species are dinoflagellates
(9). Dinoflagellates comprise a widely diversified group of unicellular

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