Relationship between cyprid energy reserves and metamorphosis in the barnacle Balanus amphitrite Darwin (Cirripedia; Thoracica)

Abstract

Nauplii batch cultures of Balanus amphitrite were reared with four different diatoms ( Skeletonema costatum, Thalassiosira pseudonana, Chaetoceros gracilis, silicate-limited C. gracilis) at three different cells concentrations: 1×10 5, 5×10 5, and 1×10 6 cells ml −1. The cyprid energy reserves were quantified as the ratio of triacylglycerols (TAG) to DNA. Energy reserves of larvae fed on different diatoms at a concentration of 1×10 6 cells ml −1 were ranked in the order: silicate-limited C. gracilis> C. gracilis> T. pseudonana> S. costatum. There was a significant linear relationship between the TAG content of the diet and cyprid energy reserves. The effect of cyprid energy reserves on metamorphosis to polystyrene surface in the presence and the absence of conspecific settlement factor (SF) was studied after 12, 24, and 48 h of incubation. A strong positive correlation between energy reserves and percent metamorphosis was observed in the absence of SF ( r 12 h=0.88, r 24 h=0.82, r 48 h=0.68, P<0.05). A weak positive correlation was observed in the presence of SF ( r 12 h=0.43, r 24 h=0.48, r 48 h=0.50, P<0.05). In both treatments, more than 80% of the cyprids with high energy reserves metamorphosed within 24 h. In contrast, a high proportion of cyprids with low energy reserves metamorphosed in response to SF in 24 h. Our results indicate that discriminatory metamorphic behavior of cyprids is closely linked to their TAG/DNA ratio, a proxy for energy reserve.