Chronic Effects of Toxic Microalgae
on Finfish, Shellfish, and
JoAnn M. Burkholder
Near centers of increasing human population growth in estuarine and coastal areas throughout many regions of the world, outbreaks of toxic microscopic algae, or microaglae, increasingly have been noted in the past few decades (Hallegraeff 1993). Other toxic microalgae, the blue-green algae or cyanobacteria, historically have affected estuaries in certain regions, and freshwaters worldwide (Carmichael 1995). Scientists debate whether the incidence of toxic microalgal blooms is actually increasing or is perceived to be increasing because of improved reporting (Culotta 1992; Hallegraeff 1993). For example, the paralytic shellfish-poisoning dinoflagellates, which many cultures worldwide historically have known to be highly toxic, seem to have significantly increased in their geographic range within the past two decades (Hallegraeff 1993). Some scientists believe that this apparent increase reflects increased monitoring for these species, especially in economically depressed subtropical regions. Although such areas previously may well have been poorly assessed, it is difficult to believe the same of countries such as the United States, which has experienced a notable increase in the geographic range and occurrence of various toxic microalgae at least since the 1970s (figure 18.1).
The “signs of the times” might best be captured by the following statistics. In 1984 scientists recognized 22 species worldwide of the most notorious of the harmful microalgae, the dinoflagellates (Steidinger and Baden 1984). Within the past 15 years, that number has increased to more than 70 (Burkholder 1998; Hallegraeff 2000). Although some of these newly recognized toxic species are cryptic members of the “hidden flora” (Smayda 1989), many have made their presence known through major discoloration of the water, or massive fish kills, or serious health effects for people who consumed toxin-contaminated seafood—