The effects of bioturbation on the infaunal community adjacent to an offshore hardbottom reef

Areas of decreased infaunal abundances in soft substrates adjacent to offsh ore hardbottom reefs may be evidence of trophic linkages between the two co mmunities. While predation may influence infaunal abundance patterns, other processes such as bioturbation may also be important by reducing infaunal abundances directly, or through an interaction with predation. In this stud y, the potential influence of bioturbation on an infaunal community is asse ssed in the sand habitat adjacent to an offshore hardbottom reef in souther n Onslow Bay off the coast of North Carolina. Transect sampling at five dis tances away from the reef indicated that holothurian, Holothuria princeps, density is inversely correlated with infaunal densities. Laboratory experim ents and field measurements of bioturbation rates suggest that H. princeps is the dominant bioturbator in the system, capable of completely turning ov er sediment immediately adjacent to the reef in as little as 6 d. Caging st udies indicate that bioturbation does not differentially affect infaunal gu ilds based on mobility mode, but has an overall negative effect on gastropo d and amphipod abundance, and infaunal rank abundances. This study suggests that bioturbation is of sufficient magnitude to influence infaunal abundan ces close to the reef, and may work concurrently with predation to produce observed infaunal abundance patterns.