Texas Great Barrier Reef

Nutrient Cycling and the Optimum Productivity of Shallow-Water Artificial Reefs And Influence of Artificial Reef Shelter Characteristics on Fish Community Structure and Production
Researchers: Alina M. Szmant, Anne-Marie Ecklund, James Bohnsack and several undergraduate and high school students.

Project Numbers and Duration: R/LR-B-34 and R/LR-B-36, 1990 - 1993 and 1993-1995

Question: The first of these related projects sought to determine whether artificial reefs with lots of internal structure trapped water-borne nutrients and boosted primary production, as well as fish numbers and diversity. When results proved inconclusive, researchers launched a second project aimed at determining how the internal complexity and structure of reefs impacted the densities, biomass and predator-prey relationships in fish.

Project: In the first project, researchers sank four sets of pyramid-shaped artificial reefs in 10 meters (32.8 feet) of water off Palm Beach County, leaving one set hollow and filling the other three with concrete rubble. They painted one of the filled reefs with anti-fouling paint to prevent all primary production. Believing that the 15 months allotted for the experiment might not be enough for natural nutrient enrichment to occur, they added fertilizer to the second filled reef. In the second project, researchers added "predator exclusion cages" to gauge how the absence of predators would impact fish populations and performed additional fish censuses at the reefs.

Results: Researchers found no difference in the amount of algae or other primary production that appeared on the fertilized and unfertilized filled reefs (though, as expected, the reef painted with anti-fouling paint remained clean). However, the researchers did find that the anti-fouled reef had a lower number of fish species, leading them to suggest that primary production at artificial reefs has a positive impact on the number of fish there. They also found that small colonial invertebrates such as hydroids added structure and habitat for small newly recruited fish. In what researchers ranked as their most important finding, they found that the filled reefs had more fishes, and a higher diversity of species, than the reefs lacking any structure. In the second project, which explored this result, the researchers found that filled reefs had significantly more Tomtate grunts, Haemulon aurolineatum, gray triggerfish, Balistes capriscus, surgeonfishes, Acanthurus spp. and juvenile drums, Equetus spp. Researchers also found that reefs protected by predator cages had many more juvenile fishes, suggesting that shelter is an important characteristic for growing fishes.

Impact: The results show that artificial reefs should be built with a large number of smaller sized and shaped crevices and holes, especially in shallow waters. The Dade County artificial reef program took this into consideration when it designed the Sunny Isles restoration project. The study also contributed to a greater understanding of coral reef fish ecology, which could lead to more accurate and efficient fisheries management.

Related Research: None.

Publications: This research was the subject of at least one dissertation and was presented at an artificial reef conference in Florida.

Quote: "The most diverse and productive communities in the oceans are coral reefs, and they are so diverse because of the variety of coral growth forms. If we want to create man-made reefs that really result in new production, we should learn from nature's own handiwork, and build into our reefs the diversity of architectural complexity that attracts such a great diversity of life forms." - Alina Szmant