Laboratory-Scale Evaluation of a Plant-Based Algaecide for Harmful and Non-Harmful Algae

Harmful algal blooms can negatively impact freshwater, estuarine, and coastal marine systems globally and pose serious risks to water quality, human and ecosystem health, and food production. Algae can produce toxic compounds, directly interfere with aquaculture species through (e.g.,) the production of foam or mucilage, as well as causing diseases and disorders in fish, and can result in hypoxic conditions when the bloom senesces. Application of US Environmental Protection Agency (USEPA) registered algaecides can be effective, scalable, and inexpensive, but there is growing interest in plant- or bacterial-derived compounds that do not require the use of chemicals such as hydrogen peroxide or copper. The algaecide C7X1 is a plant-based organic algaecide that proves effective against a wide variety of algae, including harmful algal species such as <i>Microcystis</i>, <i>Heterosigma</i>, and <i>Pseudo-nitzschia</i>. Performance is comparable to other USEPA-registered algaecides, with low to moderate extracellular toxin release and a potential lifetime of weeks in treated waters. The mode of action is inhibition of photosynthesis, suggesting that direct off-target impacts on zooplankton and other organisms would be minimal.