An extensive bloom of the brevetoxin-producing Karenia brevis occurred from 2017 to 2019 in Florida. The economic, environmental, and human health impacts were quite severe during this event. This regional project applies new field, laboratory, and modeling approaches to better understand and predict interannual variation in the magnitude and duration of Florida red tides as well as the physical, chemical, and biological factors associated with K. brevis bloom termination.

Why We Care
Blooms of the toxic dinoflagellate Karenia brevis occur almost annually in the eastern Gulf of Mexico and results in significant human, environmental health and economic impacts. K. brevis produces brevetoxins that accumulate in shellfish, and harm marine ecosystems, killing fish, marine mammals, birds and turtles. K. brevis blooms often require shellfish harvesting and fisheries closures. Brevetoxins can be aerosolized by wave action, causing respiratory problems among beach goers and coastal residents. These events can devastate local economies and ecosystems and greatly impact human health. As exemplified by the recent 2017-2019 bloom that killed nearly 600 sea turtles, 200 manatees, and 150 dolphins, prolonged red tide events have become the focus of public and political scrutiny. This prolonged bloom coincided with several extreme events (Hurricane Irma, Tropical Storm Gordon, and an extremely wet summer), and their role in this bloom is unknown. This red tide event highlights the need to address two critical aspects of K. brevis bloom ecology: the role of extreme events that potentially magnify the intensity or duration of blooms, and the factors that ultimately lead to bloom decline.

What Are We Doing
This project will apply new field, laboratory, and modeling approaches to better understand interannual variation in K. brevis blooms in the eastern Gulf of Mexico and the physical, chemical and biological factors associated with bloom decline.

Three hypotheses will be addressed:

1. Interannual spatial and temporal variability in the magnitude of K. brevis blooms on the western Florida shelf is a function of physical factors, including deep-ocean interactions with the shelf slope, wind and precipitation patterns resulting from extreme events.
2. Nutrient supply supporting blooms varies with extreme events both directly (more runoff of dissolved nutrients, increasing bloom intensity), and indirectly in supporting prey upon which K. brevis may feed, that in turn gains a growth advantage and an ability to be sustained when inorganic nutrients become depleted.
3. Bloom dispersal and termination result from specific physical, chemical and biological factors, acting alone or in concert.

Historical bloom analysis, measurements of the predominant physical forcing mechanisms acting on bloom expansion and termination, and laboratory and field measurements of nutrient supply, mixotrophy and associated bacterial and viral communities will be utilized in order to address the hypotheses. These data will populate new mechanistic models of K. brevis, to be developed within an open source physical and biogeochemical framework. It will be then applied in scenario testing and forecasting of the impacts of a) large scale climatological extreme events, b) microbial interactions, and c) mixotrophy on K. brevis blooms.

Such knowledge is absolutely critical for effective bloom management, including modeling that will allow for longer-term prediction than is currently possible, minimization of bloom-related economic damage to marine industries and tourism, and the development of targeted mitigation efforts.

Dr. Cynthia Heil of Mote Marine Laboratory leads this project. Co-investigators are Drs. Shady Amin (New York University-Abu Dhabi), Patricia Glibert (University of Maryland), Katherine Hubbard (Florida Fish and Wildlife Conservation Commission), Ming Li (University of Maryland), Joaquín Martínez Martínez (Bigelow Laboratory for Ocean Sciences), and Robert Weisberg (University of South Florida). The project is funded through the NCCOS Ecology and Oceanography of Harmful Algal Bloom (ECOHAB) Program.