Inhibitory effect of 2,4-dibromophenol and 2,4,6-tribromophenol on settlement and survival of larvae of the japanese abalone haliotis discus hannai ino

We examined the inhibitory effects of 2,4-dibromophenol (DBP) and 2,4,6-tribromophenol (TBP), which are released by the large perennial brown algae Eisenia bicyclis and Ecklonia kurome, on settlement and survival of veliger larvae of the Japanese abalone Haliotis discus hannai. The proportion of larvae attached to a polycarbonate chip coated with pregrazed diatom films and abalone trail mucus reached 70% by 2 h, and the proportion of larvae that underwent metamorphosis rose gradually to 65% at 8 h and 85% at 24 h. DBP and TBP at 1 ppm had no effect on larval health or settlement. However, in the presence of 10 ppm DBP, the proportions of larvae attached and metamorphosed were reduced to less than 15% and less than 2%, respectively, and those of overturned and dead larvae were increased to 50% and 41% at 24 h, respectively. In the presence of 10 ppm TBP, the proportion of metamorphosed larvae was reduced to 53% and that of overturned larvae increased to 30% at 24 h. All larvae exposed to 50 ppm DBP or TBP died after 2 h or 8 h, respectively. These findings suggest that DBP and TBP strongly inhibit attachment, metamorphosis, or both at 10 ppm, and that DBP is more toxic than TBP. DBP and TBP may explain low recruitment levels of abalone in kelp forests.