The southwest coast of Florida experiences near-annual blooms of the toxic dinoflagellate Karenia brevis, resulting in extensive wildlife mortalities and risks to human health. The ecological role of anthropogenic contributions of dissolved organic matter (DOM) from sources such as urban stormwater runoff (USR) and atmospheric deposition (AD) in supporting coastal K. brevis bloom populations is unknown.  We examined the bioavailability of DOM in USR from two urban-residential sites (USR-1,USR-2), as well as AD (wet) collected from Pinellas County, Florida to non-axenic laboratory cultures of K. brevis in a 6-day bioassay experiment. Labile DOM compound classes and K. brevis degradation products were identified using Excitation Emission Matrices (EEMs) generated by fluorescence spectroscopy coupled with parallel factor analysis (PARAFAC) comparing changes in the fluorescence properties of DOM at the beginning and end of the incubation. Results showed the K. brevis-dominated microbial community transformed compounds which correspond to humic-like components in the USR treatment spectra. The highest overall biomass was measured in the USR-2 treatment at 594,921 cells L ^–1 which was more than double the maximum cell density of controls. These results confirm that inputs of stormwater runoff and AD from urbanized landscapes contain a pool of bioavailable DOM compounds that can contribute to the growth of K. brevis and have important implications for coastal blooms and DOM mitigation strategies.  

Primary Presenter: Amanda Muni-Morgan, University of Florida (a.munimorgan@ufl.edu)

Authors:

Mary Lusk, Soil and Water Quality Laboratory, Gulf Coast Research and Education Center, University of Florida, Institute of Food and Agricultural Sciences, 14625 CR 672, Wimauma, FL, USA  (mary.lusk@ufl.edu)

Cynthia Heil, Mote Marine Laboratory, 1600 Ken Thompson Parkway, Sarasota, FL 34236, USA   (cheil@mote.org)