17.3 Wednesday, Jan. 4 Maximizing feeding in minimal flow: behavioral and morphological plasticity of Balanus glandula CUSHMAN, K.C.*; MERZ, R.A.; Swarthmore College; Swarthmore College email@example.com
Phenotypic plasticity is one mechanism by which intertidal organisms can thrive in a variety of local flow environments. The barnacle Balanus glandula exhibits plasticity in both its feeding behavior and the morphology of its feeding cirri. In general, barnacles feed actively at lower flow speeds, but transition to feeding passively at higher speeds, thus taking advantage of ambient currents instead of using metabolic energy to create flow. Additionally, individuals in habitually low flow environments have longer and thinner cirri than barnacles in high flow regimes. This allows high flow barnacles to feed in velocities that would deform slender low flow cirri. We hypothesized that long thin cirri are advantageous for feeding in slow velocities and that passive feeding can occur at lower speeds. We compared barnacles from two areas of Argyle Lagoon, WA- the tidal channel (flows ranging from 0-70 cm/s) and the adjacent bay (flows ranging from 0-6 cm/s). These areas share the same water supply, so both groups of barnacles experience the same temperature, food supply and larvae. In a flow tank, barnacles were placed in water velocities varying from 0-12 cm/s. Low flow barnacles employed passive feeding over about two-thirds of this range, with a decreasing ability to feed in high flows already apparent at the fastest speeds. In contrast, high flow barnacles fed passively over only the upper half of these velocities, with increasing passive feeding at higher speeds. If passive feeding requires less energy than active feeding, then barnacles benefit from the ability to feed passively in the flows they regularly encounter. Having long thin cirri reduces the total range of velocities at which a barnacle can feed, however this cirral form allows barnacles to feed using less energy in slower flows.