Inhibition and induction of barnacle settlement by natural products present in octocorals.

Barnacle settlement inhibitors and inducers are present in the gorgonianLeptogorgia virgulata and the pennatulaceanRenilla reniformis. The inhibitors are low-molecular-weight compounds (<20,000 daltons) that were detected in soft tissue homogenates and dialysates of homogenate and in ambient "gorgonian water." Settlement was almost completely inhibited at a dialysate concentration of 1.0 g wet weight equivalents/liter. The inhibitors probably function in chemical defense against predation and fouling, and could prove useful in ship fouling control. The settlement inducers are high-molecular-weight substances (>20,000 daltons) that adsorb to surfaces.