Filter feeders and plankton increase particle encounter rates through flow regime control

Abstract

Collisions between particles or between particles and other objects are fundamental to many processes that we take for granted. They drive the functioning of aquatic ecosystems, the onset of rain and snow precipitation, and the manufacture of pharmaceuticals, powders and crystals. Here, I show that the traditional assumption that viscosity dominates these situations leads to consistent and largescale underestimation of encounter rates between particles and of deposition rates on surfaces. Numerical simulations reveal that the encounter rate is Reynolds number dependent and that encounter efficiencies are consistent with the sparse experimental data. This extension of aerosol theory has great implications for understanding of selection pressure on the physiology and ecology of organisms, for example filter feeders able to gather food at rates up to 5 times higher than expected. I provide evidence that filter feeders have been strongly selected to take advantage of this flow regime and show that both the predicted peak concentration and the steady-state concentrations of plankton during blooms are Ϸ33% of that predicted by the current models of particle encounter. Many ecological and industrial processes may be operating at substantially greater rates than currently assumed.biological fluid dynamics ͉ coagulation ͉ phytoplankton ͉ suspension feeding

Particle capture mechanisms in suspension-feeding invertebrates

“…That is, a true sieving process in which all particles will be retained if greater than some minimal diameter determined by aerosol filtration theory, which takes into account particle size relative to the diameter and spacing of cylindrical wires in the mesh. In most cases, scales of relative velocity and physical length are small enough to ensure creeping flow at Reynolds number (Re) << 1, but there are cases of Re > 1 for which Humphries (2009) has shown that encounter rates of particles increase significantly above those predicted by traditional aerosol theory based on creeping (laminar) flow.…”

“…of the porous structure and shows to what extent particles less than the pore-size may intercept the elements, all depending on geometry, particle size and Reynolds number. Here the case of the intermediate Reynolds number range (0.1 to 50) has been studied by Palmer et al (2004) and more recently by Humphries (2009). The fraction of particles that stick when making contact is called the 'striking coefficient' (Jumars 1993).…”

“…The tentacle structures and ciliary particle capture mechanisms in bryozoans have been studied thoroughly over many years (Atkins 1932, Lutaud 1973, Gordon 1974, Ryland 1976, Winston 1977, Strathmann 1982, Strathmann & McEdward 1986, Gordon et al 1987, Nielsen 1987, 2001, 2002a,b, Mukai et al 1997, Riisgård & Manríquez 1997, Nielsen & Riisgård 1998, Riisgård et al 2004, 2009). The lateral ciliary bands of bryozoan tentacles produce feeding currents directed down into the lophophore and out between the tentacles (Figs.…”

Fluid Interactions That Enable Stealth Predation by the Upstream-Foraging Hydromedusa Craspedacusta sowerbyi

“…EVR for C. sowerbyi assumes that the dominant prey encounter mechanism is direct interception and relies upon Re ranging from 0.2-2 around the tentacles. We can estimate the EVR using intermediate Re estimates (Humphries, 2009) …”

Selective particle capture by asynchronously beating cilia

“…For example, at high Reynolds number (Re), diffusive deposition is negligible, while the compression of streamlines around the feeding structure provides a potential mechanism for increased encounter of particles. 5 At low Re, inertia is negligible and the feeding structure has to manipulate the surrounding fluid to generate feeding currents that bring suspended particles closer to the feeding organ.…”