In the relatively nutrient-poor offshore waters of the eastern Gulf of Mexico, destructive blooms of Karenia brevis cause environmental and economic destruction. We studied how this marine alga initiates and sustains high biomass blooms for extended periods under seemingly low nutrient conditions. Our data will support K. brevis bloom management and mitigation activities.
Why We Care
In January 2005, a Karenia brevis bloom was first detected 25 miles offshore of St. Petersburg, Florida. This bloom persisted through January 2006, and is one of the most destructive blooms recorded in the last 50 years. The bloom affected broad areas of Florida, Mississippi, and Alabama, resulting in massive fish kills; bird, turtle, and manatee deaths; extensive commercial shellfish bed closures; and a benthic mortality event that affected more than 2,000 square kilometers off the west central Florida coast.
Although classified as a coastal bloom species, Karenia brevis blooms over a wide range of nutrient conditions and commonly initiates growth in low-nutrient offshore waters of the eastern Gulf of Mexico. Information is lacking about the entire scope of bloom initiation, maintenance, and decline over the appropriate geographic and oceanographic scales.
What We Did
We used local and national scientific expertise in a collaborative laboratory and field program over multiple years to examine the diverse inter-annual physical, chemical, and biological conditions that characterize K. brevis blooms on the west Florida shelf.
We investigated two outstanding questions that must be resolved to improve K. brevis bloom management and mitigation activities:
- What nutrient sources (nitrogen and phosphorus) fuel the massive, persistent biomass blooms?
- Where are these nutrients coming from?
Our multidisciplinary team of scientists focused on comparing the physical, chemical, and physiological characteristics of K. brevis during three bloom stages (initiation, maintenance, and decline) and in three different bloom environments (lagoonal, estuarine, and coastal). The team was fortunate in that each of the four project field years experienced a different bloom condition, each of which was sampled during a phase that was roughly analogous to one of the three different bloom stages of K. brevis.
What We Found
We found that nutrient sources supporting K. brevis blooms are multiple, diverse, and complex. We quantified and evaluated known nutrient sources for relative significance. The greatest nutrient sources were the decay and recycling of the cyanobacteria (blue-green alga) Trichodesmium bloom biomass and nutrient release from zooplankton grazing, followed by the decay of red tide–related dead fish, then benthic nutrient flux, photochemical nutrient production, nitrification and Trichodesmium nitrogen fixation, and lastly estuarine inputs and pelagic nitrogen fixation. New nutrient sources identified and quantified included nitrification, photochemical nutrient production, microzooplankton grazing, pelagic nitrogen fixation and Trichodesmium biomass decay. Many of these sources alone were sufficient to support observed bloom biomass.
Project partners included the Florida Fish and Wildlife Conservation Commission’s Fish & Wildlife Research Institute, the University of Miami, Mote Marine Laboratory, Old Dominion University, the University of Maryland, and the University of South Florida.
Project data are housed in a Microsoft Access database at the Mote Marine Laboratory in Sarasota, Florida. For more information on these data, contact Dr. Kellie Dixon.
Benefits of Our Work
Understanding the sources of nutrients that support coastal harmful algal bloom events is critical to determine effective management strategies. K. brevis blooms initiate offshore, but only reach high biomass levels in nearshore waters. Effective K. brevis harmful algal bloom management and regulatory interventions are stymied by the lack of an integrated understanding of how nutrients, particularly organic nutrients, regulate these blooms temporally and spatially. This project provides the data necessary to identify regulatory alternatives and to develop improved forecasting models. The project couples results with public outreach targeting resource managers, decision makers, stakeholders, and the general public via symposiums, workshops, newsletters, public seminars, and websites.
Specific management recommendations developed from the research results are:
- Efforts should be made to reduce as much as possible potentially controllable nutrient inputs and sources that contribute to K. brevis blooms, with the understanding that, given the complexity of K. brevis bloom dynamics, no direct impact on frequency or magnitude of blooms may be immediately evident as a result.
- Water quality monitoring programs should include monitoring of both inorganic and organic forms of nitrogen and phosphorus nutrients in coastal systems. Currently most monitoring programs focus on inorganic nutrients, or total nitrogen and phosphorus.
- Localized urea (a nitrogenous compound found in urine) inputs from scales of meters to kilometers should be controlled as much as possible.
- Effective targeted communication of scientific results to the public and stakeholders remains a challenge for all aspects of K. brevis science. Outreach efforts should focus on communication and presentation of timely, accurate science to targeted audiences using professional communicators where possible.
- Harmful algal bloom monitoring efforts at both state and federal levels should include monitoring for known physical conditions that favor/disfavor the initiation, transport and export of K. brevis blooms in the southwest Florida region.
- Continue the provision of red tide related monitoring products that allow for effective targeting of monitoring needs with reduced fiscal and manpower resources for state harmful algal bloom managers (e.g., particle tracking products).
- The feasibility and potential methodologies for estimation of dead fish during red tides should be evaluated for provision of reliable economic impact data for K. brevis blooms.
- Identify and provide the funding necessary to maintain the southwest Florida coastal observing system infrastructure on an operational basis. This system has shown its utility for the provision of red tide related monitoring and forecasting products as well as event response application (i.e., forecast models for oil transport and impacts of the Deepwater Horizon oil spill).