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 inte ractions operate. We address factors determining patterns of recruitment, a nd how these patterns relate to adult infaunal community structure on the c ontinental shelf of North Carolina, USA. During spring and summer, algal an d inorganic-nutrient enhancement of trays containing defaunated sediment ca n 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, r espectively. Distance from the hardbottom habitat had little effect on recr uitment into trays of defaunated sediment during spring and summer, but rec ruitment of many taxa was higher at 10 than at 75 m from the escarpment dur ing autumn. Infaunal densities in ambient substrate were similar to those i n control trays for most taxa during the spring, but showed nearly the oppo site pattern in the autumn, with many major infaunal groups being more abun dant at 75 vs. 10 m in ambient sediment. This suggests that post-settlement processes are important in structuring the benthos in this system. Our res ults suggest that densities of recruiting infauna respond to detrital and n utrient enhancement of the sediment on the scale of a meter or less. Dislod ged macroalgae from adjacent hardbottom areas may be critical in determinin g infaunal recruitment patterns. Results are equivocal as to whether recrui tment structures these infaunal communities. Post-recruitment predation by predatory fish that come off the hardbottom escarpments to forage in the sa nd 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. (C ) 1999 Elsevier Science B.V. All rights reserved.