INTRODUCTION:

Historically, artificial reefs have been constructed of a wide assortment of materials of opportunity (derelict ships, auto bodies, refrigerators, concrete rubble, used tires, and the like). Although materials of opportunity are still in use, in recent years, marine structures have been designed specifically to function as artificial reefs. However, few studies have examined the suitability of these materials for reef construction in terms of their efficacy in acquiring diverse floral or faunal assemblages. A tire-concrete aggregate, has been suggested as an environmentally positive alternative to the usual gravel-concrete aggregate. This study compares the fish and invertebrate assemblages on co-located reefs constructed of three materials: gravel-concrete aggregate and tire-concrete aggregate tetrahedrons and limestone boulders.

METHODS AND MATERIALS:

• Fish and invertebrate assemblages were inventoried bimonthly on 12 artificial reefs constructed of either quarry rock, gravel-concrete aggregate or tire-concrete aggregate, four reefs of each material.

• The reefs were initially deployed 18 June 1998 in approximately 7m of water offshore Miami Beach at 12 predetermined sites (Figure 1).

• Four quarry stone reefs were constructed with 50, 1.2-1.5m boulders in a two layer configuration (Figures 2 & 3).

• Eight concrete reefs (4 concrete-gravel & 4 concrete-tire) were constructed with 25, 1.5m and 25, 1.2m tetrahedron modules produced by CSR Rinker under license agreement with Stability Reefs Inc. (Figures 2 & 4).

• A fish census was accomplished bimonthly by SCUBA divers recording data under- water on plastic slates.

• Fish species, abundance, total length, and lobster abundance were recorded.

• Data were analyzed with analysis of variance techniques (ANOVA) and a Student-Newman-Keuls test between means using Statistical Analysis Systems (SAS) software.

• Invertebrates were surveyed with the goal of determining if some species show preference or avoidance for any one material. We made a targeted search for species found on one substrate but not others.

RESULTS:

• Fish censusing resulted in counts of 86,129 total fish of 133 species.

• No significant differences found in:
  • Total fish abundance, all species combined (Figure 5).
    
  • Fish biomass by size class or overall total amongst the three reef types (Figure 6).
    
  • The total number of lobsters on the different reef types (Figure 7).
    

• Significant differences found in:
  • Total number of fish species (p<0.05) (Figure 8).*
    
  • Seasonal differences across all reefs for total fish, total biomass and total species (p<0.05) (Figures 5,6,8).
    

• Invertebrate census yielded 8 phyla containing 51 families and 88 species.

• There was no clear indication of invertebrate selectivity to a particular reef type(s).

CONCLUSIONS:

Whereas at the end of 12 months of research no biological differences were noted among the reefs composed of the differing materials, at 24 months this no longer appears to be the case. However, the differences in species between reef types appears to be due to a single reef (B1) that differs from the replicate boulder reefs. Elimination of this reef from the statistical analysis removes all differences in fishes between all three reef types. Further monitoring will continue for an additional 12 months.

ACKNOWLEDGEMENTS:

We thank Ben Mostkoff and Dr. Robin Sherman for aid with project design and implementation and a multitude of students at NSUOC who served as dive buddies. This research was funded in part by Florida Department of Environmental Protection and the City of Miami Beach.

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