Bioassay experiments for screening biocidal antifouling paints using CIELAB-based colorimetric analysis of fragmented green ( Ulva aragoënsis ) and brown ( Ectocarpus sp.) macroalgae

This study describes the development of a CIELAB color-based method for screening biocidal antifouling paints using fragmented green (Ulva aragoënsis) and brown (Ectocarpus sp.) macroalgae, which exhibit distinct attachment and growth behaviors. Significant correlations between dry weight and CIELAB color parameters enabled the precise adjustment of test suspension densities. Viability assessments confirmed that the algae retained full growth capacity for up to 10 weeks when stored at 5 °C in total darkness. Analytical results of antifouling bioassays using 0–40 wt % Cu2O revealed that the inhibition rate of color change (IRCC) for U. aragoënsis (after a 24-h exposure followed by a three-day recovery assessment), the cell mortality rate (CMR) for Ectocarpus sp. (after a 24-h exposure), and the daily total color difference between the control and Cu2O groups (ΔE*Bio) for both species exhibited a strong, exponential dose-dependent response to the biocide concentration. These findings demonstrate that CIELAB-based quantification provides an effective, non-destructive, and visually consistent tool for screening biocidal antifouling paints.