The Occurrence of “Green Tides”— a Review

The eutrophication, or nutrient enrichment, of coastal waters as a result of man's activities is now widely recognized as a major, world-wide pollution threat. Essentially, the increased anthropogenic source of inorganic plant nutrients interferes with the natural annual nutrient cycles and can artifically enhance primary production during periods when activity is normally low. This can have quite considerable ecological consequences for both pelagic and benthic organisms. For example, phytoplankton activity will be increased (Hoogweg et al. 1991) and, although this can be generally beneficial by increasing fisheries (Raymont 1947; Fonselius 1978; Elmgren 1989), there is some evidence that it has resulted in the occurrence of some phytoplankton blooms, both toxic and non-toxic, which have had serious effects on local fisheries and leisure activities (Braarud 1945; Ruud 1968; O'Sullivan 1971; Zou and Dong 1983; Rosenberg 1985; Kimor 1991). One such bloom occurred in the northern Adriatic in 1988 when large quantities of mucilaginous material was washed up on many tourist beaches (Degobbis 1989; Vukadin 1991). A number of authors have similarly speculated on the possible relationship between eutrophication and the occurrence of toxic blooms of microalgae in the North Sea (Cole 1972).