Texas Great Barrier Reef

The Effects of Man Made Structures on Nearby Resident Fish Communities
Researchers: William Alevizon, J.C. Gorham and several graduate research assistants.

Project Number and Duration: R/LR-B-20, 1985 - 1987

Question: The classic debate over artificial reefs is whether the reefs increase fish numbers or merely concentrate fish in one place. Could a carefully controlled study of the impacts of artificial reefs on the fish communities in a Florida marine sanctuary help move this debate in one direction or the other?

Project: Researchers counted and identified the fishes living in a flat, sandy habitat in two six-hectare (14.8 acres) study sites in Looe Key National Marine Sanctuary in the Florida Keys. Next, they built two artificial reef groups, each consisting of 12 small PVC- and concrete blocks, near the sites. They then censused the fishes in the study sites every three months for one year.

Results: Of the five most abundant species - green razorfish, Hemipteronotus splendens, pearly razorfish, H. novacula, rosy rasorfish, H. Martinicensis, slippery dick, Halichoeres bivittatu and the sand seabass, Diplectrum formosum -- researchers saw no change in the total numbers of adult and juvenile fish on the sandy habitat, or in the proportion of one species to another, in the pre- and post-reef censuses. The researchers next took the project a step further, building a large artificial reef at the center of one reef group. Nine months later, numbers of all but one of the most common species had increased 100 percent - yet numbers remained unchanged on the natural reef group. Both the earlier and later results appear to demonstrate that, at least in this case, artificial reefs resulted in an increase in fish stocks rather than a concentration of existing stocks.

Impact: By demonstrating one scenario in which artificial reefs did not have a negative impact on surrounding fish populations, the results provided support to public and private efforts in Florida to develop new artificial reefs and enhance existing ones. Through studies such as this one, artificial reefs are coming to be seen as more than just convenient 'fish attractors' In a report on the project, Alevizon wrote, "...The rational use of manmade reefs may substantially extend our ability to protect natural endangered systems, by providing the option of increasing available suitable habitat."

Publications: At least two articles about this research appeared in the Bulletin of Marine Science.

Related Research: The researchers also used the reefs to test the hypothesis that increasing the nooks, crannies and other structural pieces of the reef would increase the stocks of young fish on the reefs. Results were positive.