Physiological condition and barnacle larval behavior: A preliminary look at the relationship between TAG/DNA ratio and larval substratum exploration in Balanus amphitrite

Abstract

Behavior of laboratory-reared larvae of the barnacle Balanus amphitrite was examined in Beaufort, North Carolina (USA), in relation to their physiological condition. Cyprid substratum exploration was monitored by means of video endoscopy using various experimental surface types (clean, biofilm, 1 and 2 wk fouled) and 2 water flow regimes (still water and ca 5 cm s-1) at room temperature (21°C). We used the triacylglycerol/DNA (TAG/DNA) ratio of small batches of larvae as a measure of physiological condition in 0 to 12 d old cyprids. The physiological condition of cyprids decreased significantly with age (p < 0.001), ratios severely dropping between 5 and 8 d. Although exploration behavior did not show much variation with age, the overall number of active exploring cyprids appeared to be age dependent. Additionally, the relationship between surface exploration behavior and age also appeared to vary with substratum type as well as flow rate. For example, fewer young cyprids (0 to 5 d old) explored unfavorable substrata (clean and biofilm treatments) than older ones in still water. Exploration responses, however, appeared to differ in relation to flow regimes (still vs moving water trials). Time spent by cyprids on surfaces before returning to the water column (nonexploratory behavior) appeared to vary in relation to age and substratum type in still water trials. Duration of exploration and distance explored by cyprids in flow generally peaked with cyprids from the 3 d cohort. Overall, our results showed that habitat selection in barnacle cyprids results from a complex relationship involving substratum type, hydrodynamics and larval age (i.e. physiological condition and competency).