Man paints the sea red

Under favourable conditions, Dinoflagellata can rapidly proliferate and form large clusters. Red tides are the most conspicuous proofs of the massive presence of Dinoflagellata. In 1986, an increase in the Dinoflagellata population of the type Gymnodium brevi caused a significant red tide along the coasts of the Gulf of Texas. It extended 500 km along the coasts and caused the death of over 22 million fish in 2 months. Mollusc fishing was banned along 3/4 of the coast of the Gulf of Texas, south of Galveston, which caused a loss of oysters for a total of 1,4 million US dollars. Bivalvular molluscs are filter feeders, which feed on plankton and which, although storing the toxins contained in these Dinoflagellata, are only partly affected by their harmful effects. Nevertheless, under special circumstances, the amount of toxins that can concentrate in each single mollusc can be lethal even for man. In the same year, hundreds of tursiops dolphins died along the coasts of New Jersey and Maryland, when the red tide moved eastwards from the western coast of Florida after surviving a fairly mild winter. In Italy, algal proliferation phenomena took place in 1975 in the coastal area south of the mouth of the Po. Between 1975 and 1976, the algae caused the death of plenty of benthic animals (i.e. that live in contact with the seabed) and fish. It is assumed that the human impact on the coastal areas and in particular the gradual increase in the discharge of urban, industrial, agricultural and zoo-technical waste water into the sea may have boosted the development of these toxic algae.

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