L Journal of Experimental Marine Biology and Ecology, 223 (1998) 39–51 Induction of larval attachment and metamorphosis in the abalone Haliotis diversicolor (Reeve) * Patrick J. Bryan, Pei-Yuan Qian Department of Biology, Hong Kong University of Science and Technology, Clearwater Bay, Kowloon, Hong Kong, China Received 6 June 1996; received in revised form 2 May 1997; accepted 3 June 1997 Abstract The attachment and metamorphic responses of veliger larvae of the abalone, Haliotis diversicolor (Reeve) to potassium chloride (KCl), gamma-aminobutyric acid (GABA) and natural cues were determined. Attachment and metamorphosis of H. diversicolor were two distinctly different responses. Attachment was characterized by larval contact with a substratum followed by crawling with the larval foot firmly attached to the surface of the substratum. This behavior began approximately 48 h post-fertilization at 228C. Larvae could detach from the substratum and continue to swim for over 96 h after attachment behavior began. Metamorphosis was irreversible and could occur in larvae that were 96 h post-fertilization. The neurotransmitter GABA, stimulated 25 attachment behavior and induced low levels of normal metamorphosis at a concentration of 10 23 24 M, but was toxic to larvae at concentrations of 10 and 10 M. KCl at 10, 20 and 30 mM concentrations above normal seawater salinity stimulated attachment behavior, but became toxic at 30 and 40 mM. Low levels of metamorphosis were induced at excess KCl concentrations of 20 and 30 mM. Single films of mucus, diatoms and three species of bacteria were not as stimulatory as a combination film of diatoms and mucus in dish assays. Survival of larvae settled in dishes coated with a film of diatoms and mucus was higher than that in dishes containing either diatom or mucus films alone. The combination of diatom film and conspecific mucus may produce a novel cue that is not present in either film alone. Observations suggest that the condition of the adults may influence cues present in mucus. Moreover, when given a choice of vertical attachment sites, H. diversicolor larvae attached more frequently to slides filmed with both diatoms and mucus than to clean or diatom-filmed slides. A combination film may increase numbers of attached larvae and reduce mortality in commercial aquaculture facilities.  1998 Elsevier Science B.V. Keywords: Attachment; Metamorphosis; Gastropod; Conspecific cue; Artificial inducer; Diatom film * Corresponding author. Tel.: 1 852 2358 7331 / 7336; fax: 1 852 2335 1477; e-mail: boqianpy@usthk.ust.hk 0022-0981 / 98 / $19.00  1998 Elsevier Science B.V. All rights reserved. PII S0022-0981(97)00156-1