Ballast water management system certification testing requirements for protists are a poor fit for the Great Lakes

Challenge condition requirements for testing of ballast water management systems (BWMS) are a poor fit with regard to protection of the Laurentian Great Lakes from aquatic invasive species, particularly with respect to protists. Though protists are abundant in the Great Lakes, required densities of cells (1000 cells/mL) meeting the 10–50 µm (“protist”) regulatory size class of the ballast water discharge standard (BWDS) are rarely achievable under ambient conditions. This deficiency drives certification testing to aquatic systems dissimilar to the Great Lakes or necessitates manipulation of intake water during testing. This requirement is unnecessary because: (1) protist cells both within and smaller than the regulatory size class are largely equivalent in their challenge to BWMS performance and their threat to ecosystems; and (2) lower densities of cells in challenge water can meet regulatory requirements; i.e. at least 100 live cells/mL in untreated discharge (control) water are required for test validity. We describe how current requirements for high densities of protists within the regulatory size class as a challenge condition in certification testing unnecessarily undermine vetting of BWMS performance and operation. We posit a range of alternatives and identify approaches to modifying challenge requirements to alleviate problems while protecting test rigor and relevancy to the BWDS. Without a change to these requirements there will be no certification testing in freshwater resources like the Great Lakes without substantial intake stream manipulation during testing, and therefore, little way to confirm whether a BWMS will perform in the Great Lakes and other freshwater systems.