STEWART, H.L: Morphological heterogeneity among zooids of encrusting colonies of Membranipora membranacea induces passive flow through the colony.

Encrusting bryozoans live in a velocity gradient at the base of momentum boundary layers in the fluid environment in which they live. As suspension feeders, their interaction with the surrounding fluid is important in filter-feeding success, which is proportional to competitive ability and fitness of the colony. Active ciliary pumping by individual zooids of Membranipora membranacea creates incurrent flow that passes over tentacled-lophophores and is expelled in ‘chimneys’; regions of non-feeding zooids surrounded by feeding zooids that have lophophores that are ~2x taller than the lophophores of non-chimney feeding zooids. This study was conducted to investigate the possible induction of passive flow induced through the colony by the interaction of ambient flow and this morphological heterogeneity among zooids. Particle image velocimetry (PIV) was used to quantify average velocity of the excurrent flow from a chimney as a function of ambient flow speed. There was a significant correlation between the velocity in the vertical direction through the chimney and ambient horizontal velocity in the horizontal direction. This suggests that there may be induced flow through colonies with chimneys, even at the low Reynolds number that characterizes the fluid environment in which they live.