Mitigating Rocky Habitat Loss Using Artificial Reefs

An artificial reef was constructed on a featureless sand bottom as mitigation for the man-caused loss of rocky-type subtidal habitat in Elliott Bay, Puget Sound, Washington from a shoreline development (fill) project. Using a list of indicator biota developed for this region, it was predicted the mitigation reef would develop a greater number of economically important fish specics and greater diversities of sessile and epibenthic biota assemblages than the development site. A total of 181,400 metric tons of quarry rock was used to construct fourteen 41 m·15 m·6 m (high) reef structures in a 2.83 ha area during May 1987. This design of a 1:2 ratio of reef material: sand bottom also accommodated the trophic level relationships normally occurring for fishes feeding from reef structures and surrounding natural habitats. The mitigation reef met the predicted development during the reefs first 8 months of submergence. Fish species diversity and densities on the mitigation reef have surpassed that observed on a rocky bottom adjacent to the development site. Some displacement of resident fish appeared to have occurred as evidenced by the greater diversity and density of flounder observed on the adjacent sand bottom compared to those observed on the sand bottom between the mitigation reef structures. Impacts of artificial reefs on benthic organisms were assessed. The density and diversity of benthic organisms decreased significantly under portions of 5- and 7-year-old Puget Sound artificial reefs on cobble and sand habitats.