Fish Bulletin 146. Man-Made Reef Ecology

This report discusses in detail findings and observations made during more than 4 years of study on three experimental multi-component man-made reefs, and one "production" model reef, in Santa Monica Bay, California (August 1960–January 1965). The multi-component replication reefs were each constructed of 333 tons of quarry rock, one streetcar, 14 automobile bodies, and 44 concrete shelters. The "production" model reef was 1000 tons of quarry rock. The study was designed to investigate various aspects of man-made reef ecosystems and to determine the optimum material for reef construction in southern California.Observations made and sampling conducted at each reef included: (i) enumeration (by estimate) of the fishes, invertebrates, and plants, (ii) sediment analysis, (iii) water temperature, (iv) water clarity, and (v) encrusting growths on each reef material.Quarry rock was determined to be the preferred reef building material (based upon cost and ease of handling), even though the concrete shelters attracted the largest number of fishes. Further, quarry rock disturbed the bottom sediments less than the other three materials.True succession, not seasonal progression, was recorded for the various encrusting organisms. During the first year, a barnacle-hydroid phase was closely followed by mollusk-polychaete, ascidian-sponge, and finally encrusting ectoproct stages. Subsequent stages involve aggregate anemones, gorgonians, and stony corals.More than 200 invertebrates (protozoans to tunicates) were recorded during this study. Notations concerning each species occurrence, growth, importance on the reef, ecological niche, and known predatorprey relationships are presented.Fish populations around each reef, and material, were assessed by: (i) species enumeration, (ii) estimates of size ranges, (iii) feeding habits, and (iv) general behavioral traits. Underwater tagging techniques were developed and employed to determine fish movements. In all, 78 species (35 families and 60 genera) were recorded. Embiotocid perches and serranids were dominant during the first two years of reef life. In time they decreased in dominance while resident species (e.g., cottids, gobies, damselfish, etc.) increased.Observed fishes were classified as reef associated or non-reef associated, based upon their requirements or association to our reefs: a reef biotype being required to satisfy one or more life processes of a reef oriented species. We further subdivided the reef associated species into semi-resident (which periodically leave the reef) and resident forms (which consistently remain on the reef).Fishing success on the reefs was two to three times that recorded for nearby natural reef areas. In some instances, due to the fish concentrating effect of these structures, angler success may be even higher.Man-made reefs can turn "non-productive" areas of the nearshore into "productive" fishing areas. Initially, these structures attract fishes from surrounding areas. With time (about 5 years in our area) a natural situation is reached and the plant and animal populations exhibit fluctuations typical of reef ecosystems