Energy content at metamorphosis and growth rate of the early juvenile barnacle Balanus amphitrite

The energetic cost of metamorphosis in cyprids of the barnacle Balanus amphitrite Darwin was estimated by quantification of lipid, carbohydrate and protein contents. About 38-58% (4-5 mJ individual_-1) of cypris energy reserves were used during metamorphosis. Lipids accounted for 55-65%, proteins for 34-44% and carbohydrates for <2% of the energy used. Juveniles obtained from larvae fed 106 cells ml^-1 of Chaetoceros gracilis were bigger (carapace length: 560-616 μm) and contained more energy (5.56 ± 0.10 mJ juvenile^-1) than their counterparts (carapace length: 420-462 μm; energy content: 2.49 ± 0.20 mJ juvenile ^-1) obtained from larvae fed 10⁴ cells ml^-1. At water temperatures of 30°C and 24°C and food concentrations of 10⁴ and 10² cells ml^-1 (3:1 mixture of C. gracilis and Isochrysis galbana) as well as under field conditions (26.9 ± 3.1°C and 2.2 ± 0.8 μg chlorophyll a 1^-1), juveniles obtained from larvae fed the high food concentration grew faster than juveniles obtained from larvae fed low food concentration until 5 days post-metamorphosis. Laboratory experiments revealed a combined effect of early juvenile energy content, temperature and food concentration on growth until 5 days post-metamorphosis. After 10 days post-metamorphosis, the influence of the early juvenile energy content on growth became negligible. Overall, our results indicate that the energy content at metamorphosis is of critical importance for initial growth of juvenile barnacles and emphasize the dependency of the physiological performance of early juvenile barnacles on the larval exposure to food.