Role of neurotransmitters in the settlement and metamorphosis of the limpet Patella ordinaria

Abstract

Settlement and metamorphosis are critical processes that determine success in aquaculture and recruitment in the wild. Only a few settlement inducers have been reported for limpets (Patellogastropoda). In the present study six assays were performed to evaluate different neurotransmitters at a wide range of concentrations as settlement inducers for Patella ordinaria larvae: 5 × 10−8 to 10−4 M gamma-aminobutyric acid (GABA), 10−7 to 4 × 10−3 M acetylcholine, 10−7 to 10−4 M 3-isobutyl-1-methylxanthine (IBMX), and 5 × 10−3 to 2 × 10−2 M potassium chloride (KCl). Filtered and UV-treated seawater without any inducer was used as a negative control and natural crustose coralline algae (CCA) and cultured biofilms of the benthic diatom Navicula salinicola as positive controls. Neither GABA, IBMX, nor KCl induced settlement. IBMX promoted larval pedal exploration. Acetylcholine at concentrations above 10−3 M induced the onset of metamorphosis (velar abscission) with an efficiency similar to that of coralline algae, but the proportion of individuals completing metamorphosis was similar to the negative control. Coralline algae positive controls offered more consistent and higher settlement rates than biofilms of the diatom N. salinicola. The present results suggest that limpet larvae respond to a limited spectrum of settlement cues. Further research is required to elucidate the importance of acetylcholine on the physiology of metamorphosis in limpets.