Discolored waters containing blooms of Karlodinium persist along the western shore of Chesapeake Bay this month.

Maryland Department of the Environment responded to a call on reddish-colored water in Back Creek (Anne Arundel County, Eastport) on August 21, 20002. Dinoflagellate plankton dominated the sample at 205,000 cells/milliliter. The dinoflagellates were dominated by Karlodinium micrum (186,000 cells/ml) and moderate numbers of Prorocentrum minimum. This region is close to areas where the bloom has been observed with samples collected from Spa Creek on August 14th that contained Karlodinium densities of 295,500 cells/ml near the bridge at Commisioners Avenue between downtown Annapolis and Eastport. Also on August 14th, a water sample collected from the main bay near the Bay Bridge at Sandy Point contained 141,245 cells/ml of K. micrum. Similar colored waters were reported by Coast Guard Auxiliary personnel from the Herring Bay region on August 17th, an area of recurrent algal blooms this year. There has been no evidence of fish health events in the region related to the extent and magnitude of the bloom.

Earlier in the month, the DNR Chesapeake Bay Water Quality Monitoring Program identified bloom densities of the dinoflagellate K. micrum (6,095 cells/milliliter) observed on Saturday, August 3, 2002 off Breezy Point. Charter boat Captain Jim Brincefield collected the sample and described the region as having patches of off-colored water. Captain Brincefield observed the bloom again on Sunday August 4th as a solid band of color from Breezy Point to the Calvert Cliffs Power Plant, an estimated 7 miles long and quarter mile wide. A water sample collected in the bloom area by Captain Brincefield tested out at 11,183 cells/ml. Similar densities of Karlodinium were observed in bloom samples also collected by Captain Brincefield north of Breezy Point dating back to July 17th near Herring Bay (11,271 cells/milliliter).

Karlodinium micrum is a common dinoflagellate in the Bay during the summer season and there is evidence that the species can produce toxins that will kill fish. Laboratory studies (Dr. Allen Place and Jonathan Deeds, Center of Marine Biotechnology, University of Maryland Biotechnology Institute, in cooperation with DNR and other researchers) have shown that densities of 50,000-60,000 cells/milliliter are sometimes toxic to fish. In the last 20 years, such densities have rarely been observed during routine monitoring of the Chesapeake Bay. Large algal blooms such as this in the Bay also have the potential to produce low dissolved oxygen events that are harmful to Bay life.