For planktotrophic larvae, the availability of food is one of the major factors thatcontrol growth and development. In the present study, feeding and starvation were investigated within the scope of survival, swimming and respiration rates of Cirripedialarvae. Adults of Pollicipes pollicipes (Pedunculata: Scalpellidae) and Elminius modestus(Sessilia: Balanidae) were collected from the Iberian Peninsula and western UK coast, respectively, and a series of laboratory experiments conducted using a novel rotating wheel immersed in a temperature controlled tank. Observations were made on larval growth, gut size, mobility and oxygen consumption in response to both the supply of food in the form of controlled algal sources, as well as starvation conditions. Resulting data were analysed and revealed notable trends in the relationship between the different functional outputs at different stages of development, up to and including the cyprid. Mono- and mixed algal cultures were tested, confirming that both barnacle species have geographical related dietary preferences. Size of algal cells was only one of the factors associated with feeding rates, while volume densities and quality of the supplied phytoplankton proved of substantial importance throughout the whole study. Under starvation conditions, swimming performance did not deteriorate during 28 hours after hatching, indicating that E. modestus nauplius II carry enough yolk reserves to proceed the search for food. Nonetheless, oxygen consumption reduced after 8 hours indicating that larvae are able to adjust their metabolism as an energy conservation strategy. This would account for the oceanic distribution of spawned larvae even under conditions of impoverished plankton supply. Increase in oxygen consumption in earlier larval stages is associated with high energy expenditure of swimming and capture of food, while during the metanauplii, stable weight specific respiration rate accompanied by reduced swimming speeds suggests an increase in non-swimming related metabolic activity, possibly reflecting a radical physiological and functional shift at this stage. The first demonstration of specific dynamic action in barnacle larvae is discussed. The details provided on specific feeding rates and development, algal preference, physiological processes and swimming behaviour of barnacle larvae, contribute to the understanding of the effect of barnacles on the phytoplankton while part of the meroplankton communities.