Process-Specific Recruitment Cues in Marine Sedimentary Systems

In marine sediments, many of the processes associated with high post-settlement mortality of infauna have similar effects on the sediment surface. In most cases the original sediment surface is either removed, buried, or mixed with subsurface sediment. The experiments reported here tested the ability of new juvenile infauna to discriminate between undisturbed and recently disturbed sediment surfaces (i.e., subsurface sediment exposed). Recently settled juveniles of two polychaete species (Nereis vexillosa and Arenicola cristata) and one bivalve species (Mercenaria mercenaria) were exposed to simulated erosional and mixing events as well as to fresh feces, burrow tailings, and feeding tracks. Where the disturbance buried or removed several millimeters of the sediment surface, the time to initiate burrowing or the percentage of individuals failing to burrow increased significantly over times and percentages for juveniles on undisturbed surfaces. In all cases the results were consistent with the hypothesis that new juveniles reject (or are significantly slower to burrow into) disturbed sediment surfaces, if the disturbance is less than several hours old. For example, 51% of nereid juveniles did not burrow when placed on subsurface sediments, whereas 100% burrowed into surface sediments; their average burrowing time on surface sediments was 29.3 s compared with 109.7 s on fecal mounds of arenicolid polychaetes or 106.1 s on burrow tailings of thalassinid crustaceans. Individuals that did not indicate acceptance of a sediment surface by burrowing were all rapidly eroded from the surface in the presence of flow. Erosion of nonburrowing individuals occurred within 90 s of initiation of flow. Burrowing individuals were not eroded. The decision as to the acceptability of a sediment was made within 30 s. These data imply that the new juveniles are utilizing cues associated with a process, the disturbance of surface sediments, in addition to the species-specific cues described elsewhere.