Chemical cues inducing settlement and metamorphosis in the fouling oyster Crassostrea madrasensis

Abstract

The Indian edible oyster Crassostrea madrasensis is an important fouling organism to the coastal waters of both east and west coasts of India, The oyster larvae were reared in the laboratory and their response to settlement and metamorphic reduction, was tested. Natural bioflims developed under field (height) and laboratory (dark) conditions, a unispecies bacterial film, unialgal films of the diatom Nitzscihia sp, and a polysaccharide organic film were tested for their ability to reduce settlement and metamorphosis. Silmilarly, neurotransmitters like L· and D-dopa, dopamine, octopamine, epincphrine, norepinephrine, cAMP, db-cAMP, isobutylmethylxanthine farskolin and the amino acids lysine. argine, phenylalanine and tyrosine were assessed far their inductive ability. Biofilms proved to be a potent source of inducers for the larvae. Unispecies bacterial films of the strain Alteromonas sp excited maximum settlement and metamorphic response. Induction by the polysaccharide film of gum arabic revealed the involvement of adsorbed organic molecules on the settlement process, The neuclotransmitter L-dopa was effective in inducing settlement and inetumorphosu, medium settlement und metamorphic were observed at a concentration of 10.5 M of L-dopa. On exposure to catecholamines, epinephrine and norepinephrine, the larvae metamorphosed Without exhibiting the characteristic settlement behavior maximum metamorphosis was observed at a concentration of 10'4 M with respect to both the catecholamines tested. Lysine and arginine proved to be effective settlement cues to the larvae. The larvae were more sensitive to lysine than arginme. Results of the present study have revealed that substratum filming is an essential factor. In the induction process and reveal the involvement of neuronal pathways to the induction of settlement and metamorphosis.