Temperature and water flow influence feeding behavior and success in the barnacle Balanus glandula

Suspension feeding is a common energy acquisition strategy for many marine organisms. Conditions in the fluid environment (e.g. flow, temperature) can influence both the flux of particles past an organism and the efficiency with which organisms retain those particles. We investigated feeding behavior in the barnacle Balanus glandula under a range of water velocities and temperatures using gut dissections to directly quantify capture rates of food particles. Overall, the percentage of barnacles observed beating was typically high (68 +/- 3%), yet gut dissections confirmed that a far lower percentage had actually ingested food particles (hydrated Artemia cysts; 22 +/- 3%). This discrepancy suggests that cirral activity may serve other functions and that simple behavioral descriptions provide a poor proxy for barnacle feeding rate. Although the delivery of cysts to the cirral net and cyst capture rates peaked at intermediate water velocities (7.5 to 20 cm s(-1)), capture efficiency (the ratio of cysts captured to cysts encountered) was highest under the slowest flow (1 cm s(-1)). Model analysis demonstrated that detailed characterization of cirral beating behavior is required to accurately predict patterns of flow-dependent cyst capture. Barnacles also showed a clear thermal optimum between 10 and 15 degrees C in both capture rate and efficiency. At high temperatures (25 degrees C), feeding was reduced due to an increase in abbreviated beating behavior, whereas at low temperatures (5 degrees C) reduced capture was likely a consequence of slower beating rate. Again, only when beating behavior was incorporated into models were patterns of temperature-dependent cyst capture accurately predicted. These results suggest that the limits to feeding success are not simply biophysical, but also behavioral in nature.