Meeting Abstract

18.1  Wednesday, Jan. 4  Sub-millisecond flow fields induced by bladderwort, the fastest known suction feeder BROWN, M D*; HOLZMAN, R; BERG, O; MULLER, U K; California State University, Fresno; Tel Aviv University; California State University, Fresno; California State University, Fresno mdbrown@mail.fresnostate.edu

Bladderwort Utricularia gibba is a carnivorous plant that captures zooplankton in underwater bladders. These modified leaf structures are highly specialized for suction feeding. However, their small size (1-2 mm) and fast action (ca. 1 ms) have obscured the underlying functional kinematics and flows. We have used high-speed digital video and flow visualization (Particle Image Velocimetry) to study U. gibba at frame rates up to 10 000 per second. A total of 34 suction events have been analyzed. At a distance 1/2 diameter from the typical gape of 200 μm, bladderwort generate peak flow speeds of up to 1.2 m/s (mean 0.2 m/s), corresponding to a Reynolds number of 200 (mean 30). Prey are ingested within 1 ms of triggering the bladder, at speeds up to 0.8 m/s. Time to peak flow speed from the beginning of suction is 0.6 ms, causing accelerations in the aspired water of up to 1300 m/s2 (mean 400 m/s2). The time course of the suction event has a distinctively steep onset, followed by a relatively constant-speed plateau. Adult fish, by contrast, accelerate water with a symmetric and smoothly varying time profile of longer duration. While the peak flow speeds generated by suction-feeding fish and bladderwort are similar, the accelerations observed in bladderwort are two orders of magnitude greater. This is a consequence of their smaller size, and the pre-stressed suction mechanism that minimizes time to peak flow speed. The spatial distribution of flow speed across the gape and along the gape agrees with flow speed distributions observed with adult fish. An analytical model of flow speed distributions, when applied to suction feeding in bladderwort, is in satisfactory agreement with the observed flow fields.