A quantitative framework to evaluate the attraction?production controversy

Artificial reefs have been proposed as a tool to mitigate impacts on natural reefs, augment natural fish production, and divert detrimental harvesting activities from sensitive natural habitats. The efficacy of this strategy depends on the extent to which artificial reefs contribute to new production or simply redistribute fish during or after settlement. Small coral reef fishes are ideal study subjects because redistribution is most likely during the larval stage, given limited dispersal of benthic stages. We develop a model that incorporates the simultaneous effects of habitat augmentation, competition among reefs for larval settlers, and post-settlement density-dependence, and propose two experimental approaches for evaluating the effects of artificial reefs on local production of natural reefs. One is based on small-scale studies using replicated patch reefs, the other on unreplicated studies using larger reefs and the Before-After-Control-Impact Paired Series (BACIPS) design. Using field data for six fish species, we estimated spatial and temporal variance and thus statistical power of both designs. Power varied among species, but in most cases was sufficiently high to detect local reductions in density of 10–40% with modest levels of replication (6–20 patch reefs or sampling dates).