Sediment destabilization by animal tubes

periments were performed on isolated individuals, in order to measure approximate spatiallimits of isolated tube effects, and on arrays of individuals at densities reported previously tobe associated with stable beds. The bed was destabilized at all densities of tubes tested, and thisdestabilization was more pronounced at the higher densities. In the field, stable beds persistdespite the frequently destabilizing influence of animal tubes . We suggest that mucous bindingof sediments by animals, diatoms and/or omnipresent bacteria explains this contradiction .I . IntroductionIndividual structures on an otherwise smooth sea bed (isolated roughness el-ements, in hydrodynamic terms) are known to cause local scour by deflecting fluidof relatively high momentum toward the bed. Such scour is seen around singleblades of marine grasses (Neumann et al., 1970; Scoffin, 1970), biogenous moundsand shell fragments (Young and Southard, 1978), and animal tubes (Gage, 1977) .In contrast to the sediment-destablizing effects of isolated roughness elements isthe widely accepted notion that sediments are stabilized by arrays of seagrass bladesand surface-evident tubes constructed by infauna . This notion has developed fromboth field observational studies (Sanders