Effects of Artificial Reef Deployment on Nearby Resident Fishes

The effects of artificial reef deployment on fish communities residing in areas surrounding deployment sites were quantitatively measured. Two arrays of twelve small (2 x I x 0.5 m) artificial reefs made up of2-in PVC pipe and concrete blocks were deployed in highly similar habitat in the Looe Key National Marine Sanctuary, Florida Keys, U.S,A. One array was designated as "control" while the other was designated "experimental." Both arrays were allowed to recruit for over a full year. Fishes inhabiting sand plain habitats in two 6 hectare study sites in the vicinity of the two artificial reef arrays were censused prior to reef deployment, and then quarterly for over I year. Statistical comparison of these data resulted in no significant changes in species richness, total numbers of adult and juvenile fishes, or population densities of the five most abundant species. Fishes residing on all reefs were censused regularly. The number of fishes inhabiting the arrays stabilized in about 4-6 months. One year after deployment of these arrays, a comparatively large artificial reef made of 2-in PVC pipe and concrete blocks was deployed in the center of the "experimental" array. Fish aggregating devices (FADs) were positioned about 1-2 m above this reef to increase the effective surface area and structural complexity. Nine months after installation of this large central reef, the numbers of adult fishes [excluding Apogon spp.] residing on the experimental array had more than doubled, but remained essentially unchanged in the control array. These fishes were mainly snapper [Lutjanidae] and grunt [Haemulidae]. Our results demonstrate that, at least in some contexts, artificial reefs can result in a marked increase in the numbers of local resident reef fishes, without notable effects on fishes dwelling in nearby non-reef habitats. The deployment of artificial reefs as a means of habitat enhancement in the marine environment has grown explosively in the last 2 decades (Bohnsack and Sutherland, 1985).However, the long-term effectsof such devices on nearby biotic communities are largely unknown. Of particular interest is the degree to which such structures result in actual increase as opposed to redistribution of fish populations in areas in which they are deployed. If artificial reefs serve mainly as aggregators, concentrating otherwise naturally dispersed fish stocks, extensive reef deployment coupled with intensive harvesting of fishes could conceivably have the counterproductive long-term effect of substantially reducing breeding populations. This might actually lower the net production within an environment of the very fishes these structures are intended to attract. Thus, basic quantitative information on the interactive effects of man-made reefs with nearby fish stocks is a fundamental prerequisite to the intelligent use of this emerging technology. There is conflicting information present in the current literature pertinent to this specific question, or to the more general question of whether deployment of such structures might result in substantial and possibly undesirable changes in proximate natural fish communities. Stone, et al. (1979) constructed a 500 tire reef adjacent to a Floridian patch reef of about the same size (in terms of substrate area covered), and concluded that reef deployment did not significantly alter the fish communities of nearby natural reefs, since most of the artificial reef resident fisheswere recruited as juveniles. Talbot et al. (1978) in Australia, Randall (1963) in the U.S. Virgin Islands, and DeWees and Gotshall (1974) in California, also concluded that artificial reefs they studied were colonized mainly by juveniles. However, these results are directly contradictory to our work in the Bahamas