Meeting Abstract

80.3  Sunday, Jan. 6  Hydrodynamic forces and moments on microscopic aquatic animals DOLINAJEC, T.H.*; KOEHL, M.A.R.; Univ. of California, Berkeley; Univ. of California, Berkeley dolinajec@berkeley.edu

Many aquatic animals are microscopic and interact with the water around them at a range of velocities in which both viscous and inertial forces are important. In spite of their biological importance, hydrodynamic forces on bodies in this size and velocity range are poorly understood. We studied how the morphology and orientation of a variety of ecologically-important microscopic marine animals (copepod, veliger larva, barnacle nauplius and cyprid larvae) affect the forces they experience while swimming in the water column, and while on surfaces (e.g. predator tentacles, benthic substrata). Our focus was on a range of velocities that these animals would encounter while swimming or while on surfaces in wave-swept habitats. We measured hydrodynamic forces on dynamically-scaled physical models because they offer a better signal-to-noise ratio and enable manipulations of orientation and posture that are not possible for real microscopic organisms. We measured drag, lift, and side forces as well as moments about three axes for each model in different orientations relative to the flow and substratum. These forces and moments can reoriented swimming animals , or push, lift, peel, or shear animals off surfaces. We found that body shape, orientation, and proximity to a surface had significant effects on the magnitudes of the forces and moments on the animals. Drag was the dominant force and lift was negligible in all cases. In contrast, orientation determined whether shearing or peeling moments were greatest on attached animals. These results indicate that the forces and moments that can tumble or dislodge organisms in this little-studied size range depend on body shape, and can vary drastically with changes in posture and orientation.