Growth and survival of juvenile barnacle Balanus amphitrite: interactive effects of cyprid energy reserve and habitat

Using factorial laboratory and field-transplant experiments, we have examined the effects of cyprid energy reserve and habitat on the performance of juvenile Balanus amphitrite. The cyprid energy reserve (quantified as total lipid content) increased linearly with increasing food (the diatom Chaetoceros gracilis) concentrations, i.e. cyprids from nauplii fed the highest (1 × 10⁶ cells ml^-1), high (5 × 10⁵ cells ml^-1), low (1 × 10⁵ cells ml^-1) and the lowest (5 × 10⁴ cells ml^-1) food concentrations had the highest (0.81 μg cyprid^-1), high (0.65 μg cyprid ^-1), low (0.45 pg cyprid^-1) and the lowest (0.18 μg cyprid^-1) energy reserves, respectively. These cyprids were induced to metamorphose in the laboratory and then transplanted to 4 field sites differing in food availability. Their performance (measured as growth and survival) was assessed on Day 6. Regardless of the site, both survival and growth were lower for juveniles obtained from cyprids with the lowest energy reserve compared with juveniles obtained from cyprids with low, high and the highest energy reserves. However, the magnitude of the effect of cyprid energy reserve on growth varied among sites. For example, juveniles obtained from cyprids with the lowest energy reserve grew larger (∼2- to 3-fold) at sites with a high chlorophyll a and low C/N ratio (indicators of surplus and high-quality food) than their siblings at other sites. This was interpreted as the result of the interaction between the negative effects of the lowest energy reserve in cyprids and the positive effect of surplus food. Adverse effects of the lowest energy reserve in cyprids on juvenile growth, however, could not be completely compensated by surplus food. Regardless of the cyprid energy reserve, juvenile growth (not survival) increased as chlorophyll a increased. This study suggests that the in situ growth of juvenile barnacles may depend on both independent and interactive effects of cyprid energy reserve (larval nutritional condition) and habitat.