Reports of population increases of phytoplankton species, also known as harmful algal blooms (HABs), are increasing in frequency along the coastal regions of the world's oceans. Many of these microorganisms are single cell dinoflagellate species that co-existing with a host of other microorganism which undergo changes in species composition, compete for nutrients, and produce bioactive compounds, including toxins. Pfiesteria piscicida (and P. shumwayae) are two HAB dinoflagellates that has been implicated in fish deaths as well as human illness, including respiratory problems, skin rashes or irritation, and short-term memory loss. Our laboratory is interested in understanding Pfiesteria dinoflagellate physiology and how it is affected by other microbes. As part of this research, we are also active in developing biosensors to detect Pfiesteria and other microbes and have become interested in aspects of coral bleaching (loss of symbiotic dinoflagellates from corals) that may be caused by bacterial infection.