Are recommended dosages of copper-based Marine Growth Prevention Systems (MGPS) effective for vessel biosecurity?

Biofouling within vessel sea chests and internal seawater systems (ISS) presents a range of operational and biosecurity issues. Marine Growth Prevention Systems (MGPS) are designed to prevent biofouling accumulation in these areas, however independent data regarding their efficacy is scarce. Sacrificial copper anode MGPS, which operate by releasing reactive copper ions, have the dominant market share. In this study, we tested copper dosages generated using cupric chloride to mimic cupric ion (Cu²⁺) generation by copper anode-based MGPS. We assessed the effect of copper dosages, including those recommended by MGPS manufacturers, on mortality of larval biofouling species (Ciona savignyi and Crassostrea gigas) and mature biofouling communities under various environmental conditions. Minimum inhibitory concentrations (MICs) were 2-3 orders of magnitude higher than MGPS manufacturer-reported dosages for both larval and mature biofouling. Efficacy varied with exposure regime, organic matter load, biofouling species, and organism development stage. Based on our results, short-term copper MGPS dosing according to current manufacturer recommendations appears insufficient to manage biosecurity risks within sea chests and ISS.