Blooms of Karlodinium veneficum can produce fish-killing toxins called karlotoxins. Toxicity varies over time, with karlotoxins increasing prior to blooms and under growth-limiting conditions. We are testing the theory that rapidly multiplying cells have a low toxin content, while slowly- or non-multiplying cells accumulate more toxins. Quantifying the inverse relationship between proliferation rates and toxicity will provide a tool to predict when K. veneficum becomes highly toxic.

Why We Care
Karlodinium veneficum is a relatively small (less than 20 microns) dinoflagellate found in temperate-subtropical coastal waters worldwide. Blooms of Karlodinium that reach high densities have been associated with ecologically and economically damaging fish kills in aquaculture and natural systems in North America, Europe, Africa, and Asia. In the eastern U.S., fish kills associated with K. veneficum blooms commonly occur in brackish aquaculture facilities and other shallow coastal areas, where harmful blooms can be a recurrent annual phenomenon. K. veneficum produces blood and cell toxins (karlotoxins) that exhibit widespread toxicity to many organisms. Current thinking is that the toxins serve as an aid in prey capture and as a grazing deterrent. Fish and invertebrate (e.g., oyster) death associated with K. veneficum blooms is just one of several known or proposed forms of “collateral damage” resulting from karlotoxin production.
What We Are Doing
(1) We are using laboratory cultures of Karlodinium veneficum to determine if karlotoxin synthesis is correlated with cell cycle phase and if the stationary phase results in cellular toxin accumulation. This also includes investigating the influence of prey (mixotrophic nutrition) on daily cell division under controlled conditions.

(2) We are conducting field sampling in Baltimore Harbor, Maryland, to determine the relationship between K. veneficum cell cycle progression, in situ (field) growth rate, and cellular toxin amounts during both bloom formation and stationary bloom phases in conjunction with light, temperature, and nutrient monitoring. The team will intensively sample a summer harbor bloom, optimizing methods to ensure proper sample processing and analyses.

(3) Field experiments in Baltimore Harbor will determine the influence of key potential growth limiters (phosphorus, nitrogen, and selenium) on in situ growth and toxicity of stationary phase K. veneficum bloom populations. Experimental field manipulations using mesocosm containers (experimental water enclosures) filled with stationary phase K. veneficum bloom samples will be incubated in situ (in the harbor). This experiment will consist of controls and treatments for increased nutrients (phosphorus, nitrogen, and selenium), microalgal prey, and decreased light to determine their effect on in situ growth and amounts of cellular karlotoxin.

The project will take place over three years, with the first year devoted to the necessary laboratory culture investigations and optimization of methods. Years two and three will involve the intensive natural bloom sampling and field mesocosm experiments, which depend on the occurrence of K. veneficum blooms.

The research will provide fundamental information on the relationship between cell proliferation events that lead to bloom formation and the production of toxins that cause fish kills and other damage to coastal ecosystems. Such information is necessary for the construction of conceptual models as possible tools in prediction and management of harmful K. veneficum blooms. The project is designed to generate not only new and important information for models (e.g., a new model that incorporates in situ growth rates with toxin accumulation), but also a specific, monitoring-friendly tool that can be used by managers to predict K.veneficum bloom toxicity.

Dr. Matthew Parrow (University of North Carolina at Charlotte) and Dr. Allen Place (University of Maryland Center for Environmental Science) are leading the project. The NCCOS Ecology and Oceanography of Harmful Algal Blooms (ECOHAB) Program is providing funding for the project.