Non-equilibrium processes structuring benthic bacterial communities following deposit feeding by a sea cucumber

Non-equilibrium models of community structure focus on the role of disturbance, recovery, and succession. We examined the disturbance effect of Isostichopus badionotus (Selenka, 1867) deposit feeding on the physical habitat and benthic bacterial communities. Physical sedi ment characteristics were compared between ingesta and egesta, and bacterial community structure was compared among ingesta, egesta, fore-, mid-, and hind-gut samples using epifluorescence microscopy and DGGE analysis of 16S rDNA. When compared with ambient sediments, fresh egesta were significantly higher in organic content and algal pigments, suggesting that these animals fed selectively. In contrast, total and metabolically active bacterial densities were significantly reduced by 33 and 60%, respectively, as sediment passed through the gut, producing disturbance patches of reduced abundance. We also compared different modes of bacterial recovery by experimentally isolating egesta from underlying sediment or overlying waters. Numerical recovery occurred between 1 and 6 h, depending on which mode of recovery (migration, recruitment, or regrowth) was precluded. In contrast to previous studies performed in intertidal settings, all forms of recolonization were significant, in the following order of importance: migration ≈ recruitment > regrowth. Species richness did not change significantly through time under any recolonization regime nor was species turnover evident; thus, bacterial communities in this subtidal habitat appear to be founder-controlled. Yet the mode of recovery did influence community structure, as reflected by a significant treatment effect. The pool of potential recruits can be restricted by the mode of recolonization; thus, patchiness in community structure and high species diversity can result even in a competitive lottery situation.