Predator effects on fouling community development

Abstract

Predation by small consumers has a demonstrable effect on the recruitment and devel- opment of sessile invertebrate (fouling) communities. However, few data are available to assess the degree to which different micropredators are functionally equivalent, and whether initial effects on recruitment translate into lasting effects on adult communities. In the present study, we used field surveys and manipulative experiments to examine the effect of 2 molluscan predators on both the recruitment of sessile invertebrates and the ultimate community development under continuous pre- dation pressure for 12 mo. The mossy chiton Mopalia muscosa dramatically reduced recruits of some species and increased those of others, but ultimately total adult cover of all species was reduced by over half relative to predator-free controls. The file limpet Lottia limatula had minimal effects on recruitment, slightly reducing recruitment of some colonial ascidians. However, limpets had no effect on the total cover of invertebrates, instead altering species composition by slightly delaying overall successional trajectories. Field surveys suggested that both predators have measurable effects on community cover, as the abundance of each predator was positively correlated with an increase in free space. Plots with both chitons and limpets had nearly 4 times the open space of no-predator plots, and 2 times the open space of plots with limpets only. Therefore, both field surveys and experimen- tal manipulations highlight the substantial impact of micropredators in determining the composition of this fouling community.