Impact of tropical storms and drought on the dinoflagellates Karlodinium micrum and Prorocentrum minimum in estuarine rivers of North Carolina, USA

Abstract

The dinoflagellates Karlodinium micrum and Prorocentrum minimum are harmful algal bloom taxa from different parts of the world. They are routinely documented in estuarine rivers in North Carolina, but there have been no known toxic outbreaks of these taxa in these rivers. P. minimum usually blooms during January–March and K. micrum is most likely to bloom during June–August. North Carolina experienced three hurricanes during autumn 1999, an ongoing drought from October 2001 to October 2002, one hurricane during autumn 2003, and remnants from seven tropical systems during August–September 2004. These weather events impacted the abundance patterns of both dinoflagellates. In the months following the 1999 storms, cell concentrations of both species were abnormally low or absent during their respective bloom seasons. During the first few months of the drought, cell concentrations of both dinoflagellates were unusually high but decreased as the drought continued. The abundance of both species seemed to be unaffected by the 2003 storm. K. micrum concentrations were unusually low during the late summer growing season of 2004. Extreme weather events may impact the presence of these potentially harmful dinoflagellates.