Global synthesis reveals that artificial reef units consistently augment fish assemblages

Artificial reef units (ARUs) are increasingly deployed along coastlines to mitigate losses of coastal habitat and biodiversity by attracting existing adult fish and enhancing secondary production of new fish. Given the wide range of reported fish responses to ARUs, it is worth synthesizing published research on them to define the extent to which they augment fish and the potential underlying causes of this variability. In a review of publications from 1976 through 2023, we found 166 studies that quantified fish responses (i.e. abundance, biomass, and species richness) to ARUs. Of these studies, 17% (n = 29) paired fish surveys on ARUs with nearby soft-sediment controls to examine differences in how habitat complexity provided by ARUs influences fish assemblages. Collectively, ARUs generally support relatively greater abundance and species richness of fishes when compared to structureless shelf environments. Of the various types of ARUs, only those designed and manufactured to mimic natural reefs have been researched sufficiently to support statistical analysis for emergent trends across space and local-scale habitat features. While the magnitude of these fish responses did not vary spatially, increasing the vertical relief of “designed” ARUs enhanced the response of fish abundance and species richness. Meanwhile, the biomass of fish responded more strongly to designed ARUs with increased rugosity. Our findings contribute to a growing body of literature that evaluates the function of and potential return on investment from ARUs and may help inform decision-making by comparing the effects of different intrinsic characteristics of ARU structures.