Flow, food supply and acorn barnacle population dynamics

Abstract

While it is widely believed that oceanographic conditions influence benthic filter-feeding organisms, linkages between water column and population processes on rocky shores have been difficult to document. Here we combine laboratory and field studies to explore the relationship between water column conditions and the feeding, growth and population dynamics of the northern acorn barnacle Semibalanus balanoides. S. balanoides feeding behavior in a flow tank was strongly dictated by flow speeds, food concentrations, and temperatures. The percentage of barnacles feeding increased with both flow speed and food concentrations, but was depressed at high temperatures. These patterns were accurately reflected in S. balanoides feeding in the field. Moreover, within and among populat i o n ~, variation in barnacle growth over a wide geographic area directly reflected corresponding variation in flow speed, food abundance, and water temperature. Flow effects on barnacles also had conspicuous population consequences. Since barnacle recruitment and growth are both enhanced at high flow speeds, barnacle density-dependent dynamics may often be strongly affected by flow conditions. Our results suggest that water column processes can powerfully affect passive filter feeding organisms on rocky shores and that oceanographic conditions may often leave a strong signature on the distribution, abundance, and dynamics of assemblages of sessile marine organisms.