Effects of UV-LED irradiation on decapod crustacean larval mortality, motility, and respiration: Implications for ballast water treatments and invasive species management.

Ballast water is a major vector for the transport of aquatic non-indigenous species among ecosystems worldwide. To comply with the International Convention for the Control and Management of Ships' Ballast Water and Sediments, vessels on international voyages commonly rely on Ballast Water Management Systems (BWMS) to meet the D-2 performance standard, often using ultraviolet (UV) irradiation as a key disinfection step. UV-light-emitting diodes (UV-LEDs) offer a mercury-free UV source with long lifespan and flexibility in wavelength selection; compared to conventional lamps, they are smaller in size and require no warm-up time. Yet, their effects on larger planktonic organisms (≥50 μm) remain poorly understood. Here, we tested the effect of UV-C-LED (λ = 265 nm) on larvae of the invasive European green crab Carcinus maenas, assessing mortality, immobility, and respiration under three UV-C doses (40, 120, and 200 mJ·cm-2). All UV-C treatments significantly reduced larval motility and respiration relative to controls, leading to increased mortality over time. Larvae required comparatively high doses (120-200 mJ·cm-2) to reach substantial inactivation, relative to doses reported for bacterial and phytoplanktonic fractions. These results provide species- and life stage-specific UV-C thresholds for the ≥50 μm size class and demonstrate the value of combining behavioural, lethal and physiological endpoints when validating UV-LED-based BWMS.