TILLACK, M.A.*; BRAITHWAITE, L.F.: Feeding Methods of Balanus eburneus and Balanus amphitrite in the Indian River Lagoon, Florida

Filter feeding of barnacles can be active or passive. Active filter feeding involves stroking the water with the filter structures, with the organisms expending significant energy. Passive filter feeding involves holding the cirri up into the water and allowing ambient current to bring them food, followed by periodic withdrawal of the cirri with their captured food. Past studies have demonstrated a trend of this prolonged extension of the cirral net in response to increased water current. In order to determine if Balanus eburneus and Balanus amphitrite employ passive feeding in high current situations and active feeding in low current situations, the cirral activity of these species from the Indian River Lagoon were observed. Barnacles occurring in the field in low current sites were compared to those occurring in high current sites. A difference in the number of feeding cirral beats per minute was found among the two species and within the species over the two current regimes. Balanus amphitrite utilized more cirral beats per minute than B. eburneus. Both species used more cirral beats per minute in low current sites compared to high current sites. Barnacles of both species were also observed in a flow tank, where they were exposed to low and high currents. Individuals did not change their cirral beats per minute as the flow was increased. The lack of response to current change in the laboratory suggests that differences of feeding in current were genetic or fixed early in ontogeny.