Historical patterns of Prorocentrum minimum blooms:
Choptank, Patuxent and Potomac Rivers.

The Choptank River consistently shows small blooms each year between 1980 and the present typically at levels below 5000 cells/ml. There have been additional observations of large Prorocentrum blooms in the Choptank River system but they have not been recorded at our permanent monitoring station.

In the lower Patuxent River, there is evidence of increases in Prorocentrum every year but the magnitude of the blooms appears to have declined since 1989 when a density of over 20,000 cells/ml was recorded. The bloom recorded in May, however, is about 2.5 times the density of the 1989 bloom.

The historical record of Prorocentrum abundances on the lower Potomac River shows a common frequency of blooms under 10,000 cells/milliliter between 1984 and 1991.  Prorocentrum blooms appeared less frequently during the remainder of the 1990's. The spring 2000 bloom of 169,600 cells/ml in early May exceeds the greatest density recorded by Maryland DNR’s monitoring program by roughly 20 times.

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