Infaunal hydraulic ecosystem engineers: cast of characters and impacts.

Biogenic forces alter sediment characteristics along several axes with important consequences for structure of benthic communities. The usual axes discussed are those of sediment stabilization versus resuspension and mobile versus temporally persistent organisms. A third axis of bioadvection is typically subsumed within the others. Here we argue that given the complex fluid dynamics resulting from the bidirectional forces that organisms exert on porewater, bioadvection needs to be examined separately. The probable major players in generation of bioadvection are described with impacts on transport both of materials and heat. Illustrations are given of the bidirectionality of bioadvection and the resultant changes in oxygenation either surficially or at depth, as well as of heat transport both laterally within the sediment and vertically.