Over one half of the world's fish production for human consumption currently comes from aquaculture while wild fisheries' yields are either stable or declining. Recurring threats from the raphidophyte, Heterosigma akashiwo Hada (Sournia) have caused extensive damage ($2-6 million per episode) to wild and net-penned fish of Puget Sound, Washington, and are believed to be increasing in scope and magnitude in this region, and elsewhere in the world over the past two decades.
The mechanism of H. akashiwo toxicity is not well understood. The toxic activity of H. akashiwo has been attributed to the production of reactive oxygen species, brevetoxin-like compound(s), excessive mucus, or hemolytic activity; however these mechanisms are not confirmed consistently in all fish-killing events or cultured strains. The difficulty of conducting research with active, toxin-producing field populations of H. akashiwo have resulted in conflicting findings from those obtained in lab culture studies, thereby limiting the ability of managers and fish farmers to respond to these episodic blooms.
The overall goal of this project is to identify the primary toxic element and the specific environmental factors that stimulate fish- killing H. akashiwo blooms, and thereby provide managers with the fundamental tools needed to help reduce the frequency and toxic magnitude of these harmful algal events. Studies to date have provided incomplete and conflicting observations on the mode of toxicity and the environmental stimulation of toxification. We propose a three-pronged approach to study the environmental controls of H. akashiwo growth and toxin production; laboratory culture experiments, field observations, and bottle and mesocosm manipulation experiments.
The project objectives are to: 1. identify the element(s) of toxic activity (inorganic, organic, or synergistic) associated with blooms of H. akashiwo and its various cellular morphologies, 2. determine the environmental parameters that stimulate the growth success and expression of cell toxicity in the H. akashiwo populations of Puget Sound.
Because previous studies have used H. akashiwo cultures with little or no toxic activity, our approach is to use a "living laboratory" to study H. akashiwo bloom ecology and toxicity using natural assemblages. Using a mobile lab at field sites where H. akashiwo cells are regularly found will enable us to fully characterize the toxic element(s) responsible for fish mortality, and the environmental factors influencing toxicity. Findings from annual field studies in late June and two rapid response deployments during major bloom events will be confirmed using laboratory studies with fresh (< 6 mo. old) isolates.
The expected outputs and outcomes are: 1. determination of the key elements of toxicity of H. akashiwo, 2. characterization of the environmental variables that influence either the induction or depression of elements of toxic activity in H. akashiwo, 3. design of a strategy for realistic mitigation of H. akashiwo activities in Puget Sound, Washington.
This project is funded by the NOAA Center for Sponsored Coastal Ocean Research's Ecology and Oceanography of Harmful Algal Blooms (ECOHAB) program.
Cochlan, W.P., Trainer, V.L. Trick, C.G., Wells, M.L., Eberhart, B.-T. L., Bill, B.D. 2013. Heterosigma akashiwo in the Salish Sea: defining growth and toxicity leading to fish kills. Proceedings of the 15th International Conference on Harmful Algae.