How many organisms are in ballast water discharge? A framework for validating and selecting compliance monitoring tools

As regulations governing the discharge of living organisms in ships’ ballast water enter into force, tools to rapidly and easily measure compliance with the discharge standards will be essential. To assess, validate, and select compliance tools, a framework—consisting of three parts—is presented: proof-of-concept, validation and verification, and final selection stages. Next, a case study describing the proof-of-concept stage is discussed. Specifically, variable fluorescence was evaluated as an approach for determining compliance with the discharge standard for living organisms ⩾10 μm and <50 μm (typically protists). Preliminary laboratory experiments were conducted, which were followed by an expert workshop to gauge the feasibility of this approach and propose hypothetical thresholds indicating when the discharge standard is undoubtedly exceeded. Subsequently, field trials were conducted to assess this approach and recommended thresholds. All results were favorable, indicating the validation and verification stages are merited to further evaluate fluorometers as compliance monitoring tools.