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Marine infaunas influence sediment chemistry, nutrient cycling, and microbial communities as they burrow, feed, defecate, and irrigate their tubes and burrows. Nonlethal tissue loss to predators or other disturbances is frequently observed in macrofaunal communities, and previous research has reported significant effects of onetime injury on animal activity. In this study, we examined the effects of injury and nutrient enrichment on sediment reworking rates of a common deposit-feeding polychaete, Clymenella torquata. Individualworms in cores were monitored in a recirculating seawater system, and their defecation and sediment mixing monitored under several experimental conditions. Worms held in control (unenriched) sediment or in homogeneously diatom-enriched sediment were injured on days 0 and 7 in a 21 d experiment. Worms held in control sediment or sediment with high surface diatom enrichment were observed in a 7 d experiment following repeated injury. Posterior segments were ablated for the injury treatments, and injury and nutrient supply treatments were crossed in all experiments. Repeated injury significantly decreased surface activities and defecation, and injured worms transported significantly less surface sediment to depth than intact worms. Microalgal enrichment at the sediment surface correlated with an increase in bioturbation; intactworms in surfaceenriched sediments were more active and more likely to hoe surface sediments to depth as evidenced by vertical profiles. These findings help explain how infaunal activities are modified by injury and food availability and can be used to improve models of bioturbation to further elucidate complex benthic community dynamics. [ABSTRACT FROM AUTHOR]

Recent advances in understanding of sediment material properties and of burrowing mechanics suggest likely differences in the behavior of organisms burrowing in mud and sand. The path of least resistance in the mud may lead an infaunal organism to burrow along a rigid wall. By contrast, in sand, force chains may prevent a burrowing organism from reaching a rigid wall. Burrowing in mud occurs primarily by the propagation of cracks. Cracks, and hence burrows, tend to propagate along rigid walls. In sand, force chains comprise collections of particles that experience much more stress than their neighbors. Stress chains tend to terminate at walls where their high density may inhibit burrowing. To test for differing effects of mud and sand on the spatial distribution of infauna, proximity to a rigid wall of two polychaetes, Alitta virens and Clymenella torquata, was measured in sand and mud. For both species the cumulative density distribution of burrow distances from the wall showed significantly more burrows near the wall than expected in both mud and sand. However, in direct sampling experiments, the more mobile A. virens showed a greater tendency to burrow at the wall in mud than in sand and strong exclusion from the immediate vicinity of the wall in sand, whereas C. torquata did not show a significant difference in distance from the wall in sand versus mud. The wall effect may be weaker for C. torquata because its limited mobility makes it less likely to encounter a wall over the course of an experiment. Our results point to the need for quantitative assessment of biases of analytical devices that rely on rigid walls, such as optodes and sediment profile imaging cameras, and suggest a possible similar bias in animal distributions around natural analogs such as rock-sediment boundaries. [ABSTRACT FROM AUTHOR]

Examines the effects of porewater hydrogen sulfide concentrations on the feeding and tube-building activity of the subsurface, deposit-feeding polychaete, Clymenella torquata, in the laboratory. Injection of buffered isotonic sodium sulfide solution; Fecal production; Tube-building frequencies.