INDUCTION OF LARVAL ATTACHMENT AND METAMORPHOSIS IN THE ABALONE HALIOTIS DIVERSICOLOR (REEVE)

The attachment and metamorphic responses of veliger larvae of the abal one, Haliotis diversicolor (Reeve) to potassium chloride (KCI), gamma- aminobutyric acid (GABA) and natural cues were determined. Attachment and metamorphosis of H. diversicolor were two distinctly different res ponses. Attachment was characterized by larval contact with a substrat um followed by crawling with the larval foot firmly attached to the su rface of the substratum. This behavior began approximately 48 h post-f ertilization at 22 degrees C. Larvae could detach from the substratum and continue to swim for over 96 h after attachment behavior began. Me tamorphosis was irreversible and could occur in larvae that were 96 h post-fertilization. The neurotransmitter GABA, stimulated attachment b ehavior and induced low levels of normal metamorphosis at a concentrat ion of 10(-5) M, but was toxic to larvae at concentrations of 10(-3) a nd 10(-4) M. KCl at 10, 20 and 30 mM concentrations above normal seawa ter salinity stimulated attachment behavior, but became toxic at 30 an d 40 mM. Low levels of metamorphosis were induced at excess KCI concen trations of 20 and 30 mM. Single films of mucus, diatoms and three spe cies of bacteria were not as stimulatory as a combination film of diat oms and mucus in dish assays. Survival of larvae settled in dishes coa ted with a film of diatoms and mucus was higher than that in dishes co ntaining either diatom or mucus films alone. The combination of diatom film and conspecific mucus may produce a novel cue that is not presen t in either film alone. Observations suggest that the condition of the adults may influence cues present in mucus. Moreover, when given a ch oice of vertical attachment sites, H. diversicolor larvae attached mor e frequently to slides filmed with both diatoms and mucus than to clea n or diatom-filmed slides. A combination film may increase numbers of attached larvae and reduce mortality in commercial aquaculture facilit ies. (C) 1998 Elsevier Science B.V.