Theses and Dissertations

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Defense Date

3-2000

Document Type

Dissertation - NSU Access Only

Degree Name

Ph.D. Oceanography/Marine Biology

Department

Oceanographic Center

First Advisor

Richard E. Spieler

Second Advisor

Richard E. Dodge

Third Advisor

Curtis M. Burney

Fourth Advisor

Stephen A. Bortone

Abstract

Although there is a long history of artificial reef use, little statistically verifiable experimentation has been done examining questions about artificial reef functionality. In a series of four studies using small artificial reefs as models, I examined the effects of manipulation of: refuge size, resident fishes, complexity, attractants, and site selection on fish recruitment and fish assemblage formation.

Each study was conducted over 18 to 24 months by divers on SCUBA doing visual censuses monthly with the exception of one study which was censused quarterly. During all censuses, fishes within 1m of the reef were identified to species, individuals were counted, and all fishes were assigned to one of five size classes (0-2, 2-5, 5-10, 10-20, and 20+ cm total length). Mean total lengths were used to calculate biomass using published length-weight relationships.

Using Rinker reef modules, a multilevel reef design with high internal complexity, deployed on sand substrate at 21m depth, I examined the effects of resident fishes on fish recruitment and overall fish assemblage formation, and secondarily, compared the results of my study to those of a similar study done at a different depth (7m), nearby. There were significant differences in recruit abundance (fishes <5 cm TL), total fish abundance, and species richness between treatments at the deep site as well as differences between the deep and shallow sites. Results of my study indicate that reef fish recruitment in Broward County water is likely not resource limited but may be driven by larval limitation or post-settlement predation. This finding, however, may be site specific. Comparison with the other study indicates differences between sites in fish abundance, juvenile abundance, species richness, and species composition.

Using Reef Ball™ artificial reef modules, hemisphere shaped reefs with a large central void space and 18 side holes, I examined differences in recruitment and fish assemblage formation on identical reefs at different depths (21m and 7m), approximately 1.5km apart. There were significant differences between sites for species richness, fish abundance (all species combined, >5 cm TL), juvenile abundance (fishes <5cm TL), and biomass. Results indicate greater juvenile (fishes <5cm TL) abundance at the shallow site but greater overall fish abundance and greater species richness deep. These results suggest important site dependent differences in both juvenile recruitment and overall fish assemblage formation.

Swiss Cheese reefs, concrete cubes with 12 tunnels of varying sizes through them, were used to examine the effects of refuge size and complexity on recruitment and assemblage formation. Significant differences were found between treatments for large fish abundance (>20cm TL), total fish abundance, and species richness. Results of this study support the importance of refuge size in both recruitment and overall fish assemblage formation, with more fishes of all size classes on large refuge reefs than small. However, there was no statistical support for a role for complexity (two refuge sizes) versus single refuge size in fish assemblage formation.

Using Reef Ball™ artificial reefs I examined the effect of floating a single, 10m, poly-propylene line suspended over the reef module. In this case, there was no significant effect of using this type of attractant. The second part of the study examined the effect of complexity versus void space on recruitment and assemblage formation by adding concrete blocks to the internal void space in the Reef Balls. In this study there was significantly greater fish abundance, juvenile abundance, and species richness on the modules with concrete blocks. These result support a clear-cut role for internal complexity in fish recruitment and overall assemblage formation.

Overall, results of this multi-part study provide important new information about the effects of various design and functional attributes of artificial reefs. In particular, the importance of complexity in design, and site selection, on recruitment and assemblage formation was further clarified.

Comments

Funding provided by Aylesworth Foundation for the Advancement of Marine Sciences and Florida Sea Grant.

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