Meeting Abstract

P1.92  Friday, Jan. 4  Sea Anemone tentacles flutter and flap in water flow in the field FULL, T. *; ROBINSON, H.E.; HOLZMAN, R.; SHAVIT, U.; KOEHL, M.A.R.; Univ. of California, Berkeley; Univ. of California, Berkeley; Tel Aviv Univ.; Technion; Univ. of California, Berkeley toryrfull@gmail.com

Many benthic marine animals use flexible tentacles to capture planktonic prey from the water flowing past them. Water velocities past tentacles determine the supply of prey and the hydrodynamic forces that can deform tentacles and wash captured prey off tentacles. We used the “Glasrose” sea anemone, Aiptasia diaphana, to study how the behavior of tentacles of different sizes affects the water velocities they experience in turbulent, wavy flow in their natural habitat. Videos made in the field (Gulf of Aqaba) of sea anemones illuminated by a sheet of laser light were used to measure simultaneously the ambient water flow (using particle-tracking velocimetry) and the behavior of tentacles of different lengths. Ambient flow was characterized by waves superimposed on a unidirectional current, and velocities varied on time scales of seconds to hours. When the current predominated, tentacles were bent over and fluttered at frequencies that were independent of tentacle length, but that matched wave frequency. Tips of long tentacles were held higher and fluttered at greater amplitude than short ones, and thus sampled a greater area of the water column. When waves predominated, tentacles were whip-lashed back and forth. Although A. diaphana can inflate or deflate their tentacles, length/diameter was independent of ambient velocity and tentacles scaled geometrically. Flexible tentacles moved with the flow, thus water velocities relative to their tips were different from their bases and could be higher or lower than ambient water speeds, and in the same or opposite direction. Our study showed that tentacle flexibility reduces forces on prey and tentacles, and these effects are more pronounced for long tentacles.