Bryozoan filter feeding in laminar wall layers: flume experiments and computer simulation

Poul Scheel Larsen, Simon Matlok, Hans Ulrik Riisgård

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    Particle paths and velocities have been determined from video recordings above single-line colonies of bryozoans (Celleporella hyalina, Electra pilosa, Alcyonidium hirsutum, Membraniporamembranacea, Flustrellidra hispida) placed at the bottom of a laminar flow flume in zones of constant velocity gradient (1-4 s-1). The laminar wall layer simulated viscous sublayers found in the field for smooth surfaces. Incurrents to lines of 3-10 zooids typically distort paths of particles approaching the colony at heights 1-2 mm above the level of lophophore inlets and theycapture particles from paths 0.7-1.2 mm above this level.The experiment was simulated numerically by computing the full three-dimensional laminar flume flow for the case of a line of 10 zooids that were modelled as sink-source pairs. Computed paths ofdiscrete 'fluid particles' show how the fraction of captured particles per zooid decreases downstream. Similar results were obtained by computing the continuous concentration distribution in the flow resulting from specifying uniform upstream concentration and sinks at zooids. Computed particle paths show the crosssectional area of approaching flow cleared of particles by the 10 zooid line colony to be about 16 times the frontal area of a simulated lophophore. Fluid particles were captured from paths about 1.3 mm above the sink. At twice the flowrate, the area cleared of particles reduced to about 7 times the frontal area while feeding rate increased by about 19%.KEY WORDS: ambient flow velocity, boundary layer, suspension-feeding, lophophors
    Original languageEnglish
    JournalVie Milieu (Special Issue: Sediment-Water Interface)
    Pages (from-to)309-319
    Publication statusPublished - 1998

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