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encrusting bryozoan, Membranipora membranacea

By Daniel Griinbaum


In bryozoans, hydrodynamic interactions among colony members can substantially affect filtering rates and access to food-rich water for zooids within a colony and for the colony as a whole. Hydrodynamic theory suggests that highly integrated (area-filling) colony architectures lead to strong interference bctwccn neighboring zooids, whereas less integrated architectures do not. The highly integrated bryozoan Membrunipora membranacea displays two morphological specializations that modify hydrodynamic interactions: internal excurrent zones (chimneys) and inducible defensive spines. In this study, possible hydrodynamic mechanisms underlying the cost of inducible defense and chimney organization were tested experimentally by culturing spined and unspined colonies under controlled flow conditions. Spines reduced colony growth rate when growth was limited by clearance rates, but not when transport of particles from upstream limited growth. This supports the hypothesis that the cost of inducible defense is primarily a reduction in clearance rate (i.e. spines cause hydrodynamic interference with feeding currents) rather than metabolic investment in spine construction. Chimneys were more closely spaced in spined than unspined colonies, consistent with a mechanism for organizing chimney formation based on responses by zooids to local hydromechanical cues rather than a rigid, colony-level control of zooid growth form (astogeny). Direct manipulation of hydrodynamic cue

Year: 2013
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