Repetitive testing of TBTO, sea‐nine 211 and farnesol using<i>Balanus amphitrite</i>(Darwin) cypris larvae: Variability in larval sensitivity

Settlement inhibition assays with mass cultured cypris larvae of the barnacle Balanus amphitrite are widely used in (anti)fouling research. In this study, TBTO, Sea‐Nine 211 and farnesol were tested repeatedly using multiple batches of larvae to study variability in larval sensitivity. There were significant differences in EC50 values among batches of cyprids of the same age and a maximum three‐fold difference between EC50 values. Larval sensitivity did not change significantly when culture duration was longer than normal (5 or 6d instead of 4d). The effect of the 3 compounds on settlement was independent of cyprid age. Notwithstanding the variability encountered, the assay is suitable for screening purposes, but for a more precise comparison of antisettlement activity improved reproducibility is desirable, which might be achieved using artificial seawater, sibling barnacles and including an internal reference in the assay.