University of California, Santa Barbara, United States
Abstract: Artificial reefs are commonly used as a management tool to enhance the resource value of marine habitats or mitigate the degradation of natural reefs due to anthropogenic stressors. However, it is unclear how the communities that develop on artificial reefs compare to the natural reefs that they are designed to mimic or how quickly species interactions develop on artificial reefs. To address these questions, we compared the development of a giant kelp forest community on a newly constructed artificial reef in southern California to that of two nearby natural reefs by measuring 13 community-level attributes over a 14-year period. We found that fish abundance and species richness were comparable to reference reefs within one year of artificial reef construction, indicating that rocky artificial reef without dense stands of giant kelp can quickly attract fish. Other ecological attributes on the artificial reef- including giant kelp abundance and biomass and the abundance and richness of sessile and mobile invertebrate communities- matched those of the natural reefs within 2-4 years. By contrast, the percent cover and species richness of understory macroalgae on the artificial reef has been slow to develop and remains significantly lower than that of the natural reefs. Short-term experiments and time series analyses of observational data from annual surveys have linked the apparent delayed development of understory algae on the artificial reef to interactions with sessile invertebrates (via competition for space) and giant kelp (via competition for light). These findings underscore the importance of considering patterns of species abundance and richness in a community context. Overall, our results show that artificial reefs can rapidly match multiple community attributes of natural reefs and highlight their conservation value in mitigating anthropogenic impacts to kelp ecosystems.