Heterosigma akashiwo has emerged as a threat to finfish and shellfish stocks resulting in significant impacts to the coastal economy. We are working to identify the mechanisms and nitrogen sources utilized by Heterosigma, which potentially provide this species with a competitive advantage. The research will enhance our understanding of key linkages between nitrogen sources and the progression of HABs, and provide a better characterization of the primary factors that impact HAB ecology. 

Why We Care

Heterosigma akashiwo is a harmful algal bloom (HAB) species, with blooms recorded in temperate, subtropical, and tropical coastal regions of both Pacific and Atlantic Oceans. It produces an as-yet-unknown toxin or suite of toxic compounds that have been implicated in extensive mortality of finfish and shellfish. In 2014, for example, a Heterosigma bloom killed an estimated 280,000 farmed salmon near Port Hardy, British Columbia, while in 2006, a bloom of Heterosigma in Puget Sound resulted in a loss of nearly $2 million to the fish aquaculture industry. Laboratory culture experiments examining the growth and physiological response of Heterosigma to nitrogen source have focused on its ability to utilize nitrate, ammonium and urea. Other nitrogen sources, such as nitric oxide (NO) may be an important but overlooked source of nitrogen to Heterosigma productivity in the natural environment.

NO is a reactive nitrogen species and the amount of NO in marine systems can be substantial, with concentrations at the sediment/water interface that are on par with other nitrogen species. In spite of its abundance, NO can be toxic at high concentrations and studies indicate that marine species avoid areas where NO concentrations are elevated. The ability to use NO as a nitrogen source adds a previously unknown dimension to the range of biochemical mechanisms employed by Heterosigma to access nitrogen in marine environments, potentially providing this species with a competitive advantage and contributing to the formation of harmful blooms.

What We Are Doing

This innovative study is a multidisciplinary, hypothesis-driven approach with both laboratory culture experiments and field studies to (1) empirically assess the molecular and biochemical responses of Heterosigma to NO input, (2) determine the effects of other nitrogen sources on uptake and assimilation of NO, (3) Measure changes in NO flux from coastal sediments when Heterosigma is present, and (4) evaluate the contribution of NO to species selection during the early stages of a Heterosigma bloom.The focus of studying a novel source of nitrogen potentially supporting the growth of Heterosigma is viewed as exciting. The series of planned experiments are logical and likely to provide meaningful information that can be used by managers.

This project specifically addresses the goals of the ECOHAB program to develop a quantitative understanding of HABs in relation to the surrounding environment by (1) investigating the factors controlling HAB growth, and (2) understanding community ecology and ecosystem dynamics including the bottom-up control of HABs. In particular, this project will contribute to our understanding of factors that fuel blooms of Heterosigma akashiwo in coastal regions.

Dr. Kathryn Coyne of the University of Delaware leads this project. Co-leads are Drs. Joanna York (University of Delaware) and Robinson Fulweiler (Boston University). The project is funded through the NCCOS Ecology and Oceanography of Harmful Algal Bloom (ECOHAB) Program.