Marine dinoflagellate cysts as indicators of eutrophication and industrial pollution: a discussion.

The results from an investigation of dinoflagellate cysts as indicators of eutrophication in Tokyo Bay, Japan, by Matsuoka [Sci Total Environ 231 (1999) 17] are discussed with reference to other pertinent literature not discussed in the original article. Both the Japanese study and previous work from Norwegian fjords show that pollution (including cultural eutrophication) may produce changes in the phytoplankton reflected by a shift from more autotrophic--to more heterotrophic--dominance of cyst assemblages. However, this is a proportional change that seems likely to result from reduced autotrophic production rather than the increased heterotrophic production suggested by Matsuoka. This is not unequivocal evidence of eutrophication, since Tokyo Bay is impacted also by heavy industrial pollution, the possible effects of which cannot be distinguished, and the quantitative method used for estimating changes in cyst productivity is flawed.