Enhancement of larval settlement and metamorphosis through biological and chemical cues in the abalone Haliotis diversicolor supertexta

Chemical and biological cues associated with substrata in the environment were considered to be the primary stimuli initiating larval settlement and metamorphosis in many marine mollusks. In present study, various settlement and metamorphosis inducers at both the laboratory and scale-up experiments were investigated to determine their effects in inducing settlement and metamorphosis on the abalone Haliotis diversicolor supertexta. In lab experiment, results showed that both bacteria and diatoms colonized on the substrata could greatly enhance the larval settlement and metamorphosis, and larval settlement and metamorphosis could be induced by exposure to natural seawater supplemented with potassium chloride (KCl), γ-aminobutyric acid (GABA) or KCl combined with GABA. Treatments supplemented with 5 mM KCl, 10 mM KCl, 10− 6 M GABA or some combinations can significantly enhance both the settlement and metamorphosis rates. And lower settlement and metamorphosis were induced by higher concentration up to 20 mM KCl or 5 × 10− 6 M GABA, which indicated that high concentrations of KCl or GABA were toxic to abalone larvae. The combination of KCl and GABA did not appear positive synergy effects than that of single supplementation. Time course experiment demonstrated that supplementing time was critical to the stimulatory effects on larval settlement and metamorphosis. In scale-up experiment, larval metamorphosis rates at 10 days after fertilization were significantly promoted by exposure to KCl or GABA at low concentration level. The inducement effects were similar to the results at laboratory scale experiment. The results imply that these inducers could be applied on the production of abalone hatchery industry.