Effects of chemical cues on larval settlement of the flat oyster (Ostrea edulis L.): A hatchery approach

The flat oyster Ostrea edulis (L.) is a species native to Europe and a highly valued product for consumption. Rearing the oyster larvae, through the settlement and metamorphosis processes, is extremely critical for researchers and the hatchery industry. Settlement and metamorphosis in marine invertebrates typically occur in response to environmental, chemical and/or physical cues. The effect of several environmental factors, bacteria biofilms and analogues of natural inducers on settlement and metamorphosis of different bivalve larvae has been reported. However, there are no studies about the effect of chemical inducers on the settlement and production of flat oyster larvae under laboratory and hatchery conditions.In the present study, competent larvae of the flat oyster O. edulis were induced to settle by exposure to the neurotransmitter GABA, l-DOPA, the catecholamines epinephrine and norepinephrine, and IBMX, under laboratory conditions. After 24h, maximum percentages of settlement were induced by 10−4M IBMX, 10−4M l-DOPA, 10−5M GABA and 10−6M epinephrine. Exposure to IBMX and norepinephrine also induced significant levels of settlement in Ostrea after 48h. In contrast, 10−4, and 10−5M epinephrine and 10−6M l-DOPA failed to induce significantly higher settlement rates than the control larvae. GABA was found to be the most effective inducer. Maximum settlement rate was achieved by 10−4M GABA (>64%), four times higher compared to the control larvae. Exposure to 10−5M and 10−6M GABA also induced a significantly higher larval settlement. Mortality of O. edulis larvae was not affected by the chemical inducers. In hatchery conditions, GABA was an active and fast inducer of settlement and metamorphosis. 10−6M GABA promoted synchronisation of larvae and positively affected the spat growth.