SETTLEMENT BEHAVIOR AND METAMORPHOSIS OF OYSTER LARVAE (CRASSOSTREA-GIGAS) IN RESPONSE TO BACTERIAL SUPERNATANTS

Veliger larvae of the oyster Crassostrea gigas (Thunberg) responded to unknown dissolved chemical inducers found in supernatants of cultures of the bacteria Alteromonas colwelliana and Vibrio cholerae. The response, which was similar to that seen when larvae were exposed to the neurotransmitter precursor L-3,4-dihydroxyphenylalanine (L-DOPA), consisted of an initial settlement phase of swimming with the foot extended and crawling on the substrate. Subsequently larvae attached to the substrate and metamorphosed. The percentage of veligers metamorphosing following inducation of settlement behavior was higher in a group of older larvae, a response similar to that seen with L-DOPA, suggesting that competence to respond to bacterial supernatants is divided into two phases: behavioral competence followed by morphogenetic competence. Following size exclusion chromatography, the molecular weight of the peak containing the activity which induced settlement behavior was determined to be ≤ 300 daltons. Autoclaved Marine Broth, which induced low levels of settlement behavior also contained this low molecular weight active peak, suggesting that an oyster settlement inducer is also present in this medium. © 1990 Springer-Verlag.