PROCESS-SPECIFIC RECRUITMENT CUES IN MARINE SEDIMENTARY SYSTEMS

In marine sediments, many of the processes associated with high post-s ettlement mortality of infauna have similar effects on the sediment su rface. In most cases the original sediment surface is either removed, buried, or mixed with subsurface sediment. The experiments reported he re 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 speci es (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 se diment surface, the time to initiate burrowing or the percentage of in dividuals failing to burrow increased significantly over times and per centages for juveniles on undisturbed surfaces. In all cases the resul ts were consistent with the hypothesis that new juveniles reject (or a re significantly slower to burrow into) disturbed sediment surfaces, i f the disturbance is less than several hours old. For example, 51% of nereid juveniles did not burrow when placed on subsurface sediments, w hereas 100% burrowed into surface sediments; their average burrowing t ime on surface sediments was 29.3 s compared with 109.7 s on fecal mou nds of arenicolid polychaetes or 106.1 s on burrow tailings of thalass inid crustaceans. Individuals that did not indicate acceptance of a se diment surface by burrowing were all rapidly eroded from the surface i n the presence of flow. Erosion of nonburrowing individuals occurred w ithin 90 s of initiation of flow. Burrowing individuals were not erode d. The decision as to the acceptability of a sediment was made within 30 s. These data imply that the new juveniles are utilizing cues assoc iated with a process, the disturbance of surface sediments, in additio n to the species-specific cues described elsewhere.