Comparison of Fish Assemblages on Artificial and Natural Reefs off the Coast of Southern California
A wide range of subtidal reefs was examined in order to evaluate the similarities between fish assemblages on artificial and natural reefs. All age classes of fish on 10 artificial and 16 natural reefs were censused along benthic and water-column transects during fall 1986. Physical characteristics of the reefs were measured and invertebrate and algal assemblages were assessed. Two types of artificial reefs were sampled. “Traditional” artificial reefs were usually small, isolated, completely submerged, and with low to moderate height. Breakwaters were larger, steeper, emergent (i.e., projected above the surface of the water) and tall. Natural reefs ranged from small, high-relief reefs composed of boulders and bedrock to extensive, low-relief reefs composed of cobbles. The mean size of artificial reefs was 2.66 ha, compared to 185 ha for natural reefs. Forty-one species of fish were sampled on the artificial and natural reefs. Artificial reefs had significantly more benthic fish species (x¯ = 18.7 vs. 14.2 for natural reefs), a greater density of benthic fishes (x¯ = 425/1,000 m3 vs. 185/1,000 m3 for natural reefs), and a greater biomass density of benthic fishes (x¯ = 30 kg/1,000 m3 vs. 22 kg/1,000 m3 for natural reefs); the diversity of benthic species was not different. The species richness, diversity, density and biomass density of fish in the water column were not different on artificial versus natural reefs. In general, the same species were found on both reef types, although the relative abundances of some of the common species differed. Nonetheless, the fish assemblages on artificial reefs were generally similar to the assemblages on natural reefs. Artificial reefs were so much smaller than most natural reefs that, in spite of their greater densities of fish, the total abundance of fish was generally much higher on natural reefs. Estimated standing stocks on artificial reefs varied from 0.12 to 2.77 metric tons (MT), with a mean of 0.94 MT. On natural reefs, estimated standing stocks varied from 2.08 to 276.05 MT, with a mean of 45.32 MT. This result has important implications for the use of artificial reefs in mitigation. Even under the liberal assumption that all fish on an artificial reef are produced by the reef rather than attracted to it, the size of artificial reef needed to compensate for environmental impacts to natural reefs may be substantial.
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Document Type: Research Article
Publication date: 1989-03-01
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