Reef-associated predators influence adjacent soft-sediment communities

Marine reserves provide a large-scale manipulation of predator densities, which provides a means to investigate the potential effects of predation. The effects of reef-associated predators were examined in northeastern New Zealand by comparing soft-sediment assemblages at sites having different densities of large predators. Large rock lobsters (Jasus edwardsii) were 3.8 times more abundant, and large snapper (Pagrus auratus) 12 times more abundant, on average, at reserve sites compared with non-reserve sites. The overall structure of infaunal communities differed between areas with high predator densities (reserve) and those with lower densities (fished). Sites with consistently higher densities of snapper and lobster were found to have a lower biomass of two bivalve species, and the greatest decreases were found near the reef edge (2-5 m). For several fauna a strong gradient in their density with distance from the reef was observed at both reserve and nonreserve sites. The hermit crab Pagurus novizelandiae occurred more frequently near the reef edge, while the heart urchin Echinocardium cordatum and bivalve Dosinia subrosea occurred more frequently farther away from the reef. The results suggest that certain species in this assemblage are affected differently by a combination of physical and biological forces. We conclude that, where reef predators are removed by fishing pressure, a resultant indirect effect is an increase in prey species in adjacent soft-sediment assemblages.