Recruitment patterns of continental shelf benthos off North Carolina, USA: effects of sediment enrichment and impact on community structure

Recruitment acts as a template against which all subsequent ecological interactions operate. We address factors determining patterns of recruitment, and how these patterns relate to adult infaunal community structure on the continental shelf of North Carolina, USA. During spring and summer, algal and inorganic-nutrient enhancement of trays containing defaunated sediment can enhance recruitment of infauna. Capitellid and opheliid polychaetes were 2 to 90 times more abundant in algal treatments, and 5 times more abundant in nutrient trays, compared to unenriched trays during spring and summer, respectively. Distance from the hardbottom habitat had little effect on recruitment into trays of defaunated sediment during spring and summer, but recruitment of many taxa was higher at 10 than at 75 m from the escarpment during autumn. Infaunal densities in ambient substrate were similar to those in control trays for most taxa during the spring, but showed nearly the opposite pattern in the autumn, with many major infaunal groups being more abundant at 75 vs. 10 m in ambient sediment. This suggests that post-settlement processes are important in structuring the benthos in this system. Our results suggest that densities of recruiting infauna respond to detrital and nutrient enhancement of the sediment on the scale of a meter or less. Dislodged macroalgae from adjacent hardbottom areas may be critical in determining infaunal recruitment patterns. Results are equivocal as to whether recruitment structures these infaunal communities. Post-recruitment predation by predatory fish that come off the hardbottom escarpments to forage in the sand flats may be more important in late summer and autumn. Experiments that are deployed at different times and over multiple spatial scales are needed to determine what factors are important in maintaining complex systems.