Erect Bryozoans Are More Than Baffling: Enhanced Sedimentation Rate by a Living Unilaminate Branched Bryozoan and Possible Implications for Fenestrate Bryozoan Mudmounds

Abstract

Feeding colonies of the branched cheilostome bryozoan Bugula nertina trap sediment more effectively from sediment-laden water flowing at velocities of a few cmls than do dead colonies, which in turn collect more sediment than bare, smooth substrata. The enhanced sedimentation immediately downstream of live colonies is due apparently to cilia-generated currents. These currents draw water, sediment and organic material, that would otherwise pass by unimpeded, through the colonies and into the stagnant region below and leeward of them. Ancient colonies with organization generally similar to Bugula (such as the Paleozoic fenestrate bryozoans) may also have generated higher sedimentation rates where slightly turbid water passed over them than passive baffling or production offeces or pseudofeces alone would generate. This potentially could have contributed to enigmatic mudmound buildups, such as the Carboniferous Waulsortian mounds, and other muddy facies.