NOAA Technical Memorandum NOS NCCOS 16

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**Coastal and Estuarine Data Archaeology and Rescue Program**

**THE USE OF LARGE ARTIFICIAL REEFS**

**TO ENHANCE FISH POPULATIONS AT DIFFERENT DEPTHS IN THE FLORIDA KEYS**

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May 2005

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height="0.6520833333333333in"}

**US Department of Commerce**

**National Oceanic and Atmospheric Administration**

**Silver Spring, MD**

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NOAA Technical Memorandum NOS NCCOS 16

![](media/image1.pct){width="6.027777777777778in" height="6.875e-2in"}

**THE USE OF LARGE ARTIFICIAL REEFS**

**TO ENHANCE FISH POPULATIONS AT DIFFERENT DEPTHS IN THE FLORIDA KEYS**

> by

Curtis R. Kruer

Florida Keys Artificial Reef Association, Inc.

Big Pine Key, FL

and

Laura 0. Causey

Big Pine Key, FL

**MARFIN Program**

**NOAA National Marine Fisheries Service**

#NA89AAHMF1 79

Originally published July, 1992

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height="4.1666666666666664e-2in"}

A. Y. Cantillo and M. J. Bello

(Editors, 2005)

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height="1.2777777777777777in"}

May 2005

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United States National Oceanic and

Department of Commerce Atmospheric Administration National Ocean Service

Carlos M. Gutierrez Conrad C. Lautenbacher, Jr. Richard W. Spinrad

Secretary Vice-Admiral (Ret.), Assistant Administrator

Administrator

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For further information please call or write:

NOAA

National Ocean Service

National Centers for Coastal Ocean Science

1305 East West Hwy.

Silver Spring, MD 20910

301 713 3020

Cover photograph: Underwater view of a mid-water prefabricated unit 17
months after placement.

Disclaimer

This report has been reviewed by the National Ocean Service of the
National Oceanic and Atmospheric Administration (NOAA) and approved for
publication. Mention of trade names or commercial products does not
constitute endorsement or recommendation for their use by the United
States Government.

**TABLE OF CONTENTS**

LIST OF TABLES i

LIST OF FIGURES v

LIST OF PLATES vii

ABBREVIATIONS ix

PREFACE xi

Abstract \[PREPARED IN 2005\] 1

1\. Introduction 1

2\. Methods 3

2.1. Overview 3

2.2. Artificial Reef Construction and Placement 3

2.3. Site Conditions 5

2.4. Sampling 6

2.4.1. Prefabricated Units 6

2.4.2. Natural and Rubble Reefs 7

2.5. Analysis 7

2.6. Foulinq Community Photography 8

3\. Results 9

3.1. Shallow reefs 9

3.1.1. Prefabricated Units 9

3.1.2. Natural Reef 10

3.2. Mid-Depth Reefs 10

3.2.1. Prefabricated Units 10

3.2.2. Natural Reef 11

3.3. Deep Reefs 11

3.3.1. Prefabricated Units 11

3.3.2. Natural Reef 12

3.4. Bahia Honda Rubble Reefs 12

3.5. American Shoal Bridge Rubble Reefs 12

3.6. Hawk Channel Rubble Reefs Combined 13

4\. Discussion of Objectives 13

4.1. Objective 1. Quantify the species composition, biomass, and
seasonality of fishes attracted and produced on large fabricated
artificial habitats over a 24 month period. 13

4.1.1. Shallow Prefabricated Units 14

4.1.2. Mid-Depth Prefabricated Units 14

4.1.3. Deep Prefabricated Units 15

4.1.4. Bahia Honda Rubble Reefs 15

4.1.5. American Shoal Rubble Reefs 15

4.2. Objective 2. Compare the community structure of reef fishes on
prefabricated habitats to nearby natural reefs. 16

4.2.1. Similarity of Units to Natural Reefs 16

4.2.2. Similarity of Rubble Reefs to Other Reefs 17

4.2.3. Comparison of Top 15 Species 18

4.2.4. Length-Frequency Comparisons 18

4.3. Objective Number 3. Evaluate the effects of reef siting at
different water depths on species composition, recruitment and biomass.
19

4.3.1. Species Composition, Frequency, and Abundance 19

4.3.2. Recruitment and Colonization 20

4.3.3. Biomass 20

4.4. Objective number 4. Separate fish communities into trophic levels
to assess location of food source (i.e. water column, surrounding
bottom, structure fouling community, etc.). 21

4.4.1. Browsers 22

4.4.2. Piscivores 22

4.4.3. Herbivores 22

4.4.4. Invertivores 23

4.4.5. Planktivores 23

4.5. Objective Number 5. Document and quantify the plant and
invertebrate fouling community as a function of substrate and water
depth. 24

4.6. Objective Number 6. Determine if large, fabricated habitats can
provide significant fishing opportunities. 25

4.6.1. Shallow Prefabricated Units 26

4.6.2. Mid-Depth Prefabricated Units 26

4.6.3. Deep prefabricated Units 27

4.6.4. Hawk Channel Bridge Rubble Reefs 27

4.6.5. Bahia Honda Rubble Reefs 28

4.6.6. American Shoal Rubble Reefs 28

4.6.7. Fishing Activity 29

4.7. Objective Number 7. Evaluate the economics of constructing,
transporting and placing artificial habitats to enhance fishery
resources and fishing opportunities. 29

4.7.1. Prefabricated Units 30

4.7.2. Bahia Honda Rubble Reefs 31

4.7.3. American Shoal Rubble Reefs 31

4.7.4. Cost Effectiveness of Artificial Reefs 32

5\. Comparisons to Other Artificial and Natural Reefs 33

6\. Conclusions and Recommendations 34

7\. Recommendations for a Continuing Artificial Reef Program in the
Florida Keys 36

8\. References 37

9\. Acknowledgments 39

Tables 41

Figures 131

Plates 149

LIST OF TABLES

1\. Summary of monitoring dates and 411 samples collected. SAR = shallow
units, SNR = shallow natural reef, MAR = mid-depth units, MNR =
mid-depth natural reef, DAR = deep units, DNR = deep natural reef, BH =
Bahia Honda rubble reefs, AMS = American Shoal rubble reefs. 41

2\. One hundred and seventy-nine species censused at artificial and
natural reefs from June 1988 to June 1990. 43

3\. One hundred and seventy-nine species censused at reefs from June
1988 to June 1990, by family. 48

4\. One hundred and eight species censused at fabricated units from June
1988 to June 1990. 52

5\. One hundred and three species censused at bridge rubble reefs in
Hawk Channel from June to August 1989. 55

6\. One hundred and fifty-three species censused on all natural reefs
from July 1988 to May 1990. 58

7\. Summary of monitoring at shallow fabricated unit 1 (SAR1) from June
1988 - June 1990. 62

8\. Summary of monitoring at shallow fabricated unit 2 (SAR2) from June
1988 - June 1990. 63

9\. Summary of monitoring on shallow fabricated unit 3 (SAR3) from June
1988 - June 1990. 64

10\. Combined summary of monitoring on 3 shallow fabricated units from
June 1988 - June 1990. 65

11\. Percent of species shared by artificial reefs (AR), between
artificial reefs and natural reefs (NR) and between prefabricated units
and bridge rubble sites. Censuses conducted June 1988 - June 1990. 67

12\. Summary of censuses on the shallow natural reef (SNR) from July
1988 - April 1990. 68

13\. Summary of monitoring on mid-depth fabricated unit 1 (MAR1) from
June 1988 - June 1990. 71

14\. Summary of monitoring on mid-depth fabricated unit 2 (MAR2) from
June 1988 - June 1990. 73

15\. Combined summary of monitoring on 2 mid-depth fabricated units from
June 1988 - June 1990. 75

16\. Percent shared of the 15 most frequent, abundant, and heaviest
species in various comparisons of reefs. 77

17\. Ranking of 15 most frequent and 15 most abundant species at the
mid-depth fabricated units from June 1988 - June 1990. 78

18\. Summary of censuses on the mid-depth natural reef (MNR) from
September 1988 - May 1990. 79

19\. Summary of monitoring on deep fabricated unit 1 (DAR1) from June
1988 - June 1990. 82

20\. Summary of monitoring on deep fabricated unit 2 (DAR2) from June
1988 - June 1990. 84

21\. Combined summary of monitoring on 2 deep fabricated units from June
1988 - June 1990. 86

21a. Ranking of the 15 most frequent and 15 most abundant species on the
deep fabricated units from June 1988 - June 1990. 88

22\. Summary of censuses on the deep natural reef (DNR) from September
1988 to May 1990. 89

23\. Summary of monitoring at the Bahia Honda bridge rubble reefs from
June to August 1989. 92

24\. Summary of monitoring at the American Shoal bridge rubble reefs in
July and August 1989. 95

25\. Combined summary of monitoring for Bahia Honda and American Shoal
reefs from June to August 1989. 97

26\. Summary of settler and colonizer species at the shallow fabricated
units from June 1988 to June 1990. 100

27\. Summary of settler and colonizer species at the mid-depth
fabricated units from June 1988 to June 1990. 101

28\. Summary of settler and colonizer species at the deep fabricated
units from June 1988 to June 1990. 102

29\. Summary of settler and colonizer species at the Bahia Honda bridge
rubble reefs from June to August 1989. 103

30\. Summary of settler and colonizer species at the American Shoal
bridge rubble reefs from July to August 1989. 105

31\. Comparison of 15 most frequent, abundant, and heaviest species at
shallow fabricated units to the shallow natural reef, June 1988 to June
1990. 106

32\. Comparison of the 15 most frequent, abundant, and heaviest species
at mid-depth units to the mid-depth natural reef, June 1988 to June
1990. 107

33\. Comparison of the 15 most frequent, abundant, and heaviest species
at the deep fabricated units to the deep natural reef, June 1988 to June
1990. 108

34\. Comparison of the 15 most frequent, abundant, and heaviest species
at the American Shoal and Bahia Honda bridge rubble reefs, June to
August 1989. 109

35\. Comparison of the 15 most frequent and abundant species on
artificial and natural reefs at similar depths 110

36\. Occurrence and rank of the 15 most frequent species at artificial
reefs. 111

37\. Occurrence and rank of the 15 most abundant species at artificial
reefs. 112

38\. Occurrence and rank of the 15 heaviest species at artificial reefs.
113

39\. Summary of species by trophic level at mid-depth fabricated units,
June 1988 to June 1990. 114

40\. Summary of species by trophic level at deep fabricate units. June
1988 to June 1990. 117

41\. Summary of species by trophic level at the deep natural reef from
September 1988 to May 1990. 120

42\. Summary of species by trophic level at Bahia Honda rubble reefs
from June to August 1989. 124

43\. Summary of close-up fouling community photography at fabricated
units. 127

44\. Comparison of artificial reefs in Hawaii and Florida (from Bohnsack
*et al.*, 1989). Stone *et al.* (1979) included a 12 m dia x 2 m high
natural reef and a 20 m dia x 1 m high tire reef. 128

LIST OF FIGURES

1\. High profile prefabricated unit design. 131

2\. Low profile prefabricated unit design. 132

3\. Study site locations in South Florida. 133

4\. Location of the study site near Big Pine Shoal and the Bahia Honda
and American Shoal bridge rubble reefs. 134

5\. Approximate location of prefabricated units and natural reefs within
the study area. 135

6\. Points of fouling community close-up photography.. 136

7\. Total number of species recorded at censused artificial and natural
reefs. 137

8\. Relative density of fishes recorded at censused artificial and
natural reefs. Excluded are 1,000 round scad in one DAR2 sample and 800
juvenile grunts in one MAR1 sample. 138

9\. Mean number of species and fishes per census at units. Excluded are
1,000 round scad in one DAR2 sample and 800 juvenile grunts in one MAR1
sample. 139

10\. Monthly numbers of species at each low profile unit. 140

11\. Monthly numbers of fishes at each low profile unit. 140

12\. Monthly number of species at each mid-depth high profile unit. 141

13\. Monthly number of fishes at each mid-depth high profile unit.
Excludes 800 MAR2 (8/88) grunts. 141

14\. Monthly number of species at each deep high profile unit. 142

15\. Monthly number of fishes at each deep high profile unit. Excludes
1,000 DAR2 (10/88) round scad. 142

16\. Potential contribution of settler species to numbers and biomass at
units. Excludes 800 juvenile grunts at MAR. 143

17\. Potential contribution of colonizer species to fish numbers and
biomass at units. Excludes three nurse sharks at SAR and 1,000 round
scad at DAR. 143

18\. Monthly comparison of settler species as a proportion of total
species at mid\[depth and deep units. 144

19\. Monthly comparison of potential settler numbers as a proportion of
total numbers at mid\[depth and deep units. 144

20\. Monthly mean number of species at units in three depths. 145

21\. Monthly total of fishes at units in three depths. Numbers are from
three shallow units and two units at mid-depth and deep sites. 145

22\. Trophic level as a proportion of total biomass at four sites. 146

23\. Trophic level as a proportion of total numbers at four sites. 146

24\. Monthly numbers of yellowtail snapper at mid-depth and deep units.
147

25\. Monthly numbers of yellowtail snapper and gray snapper at deep
units. 147

LIST OF PLATES

1\. Construction yard view of low profile (top) and high profile
(bottom) prefabricated units. The view of the high units is prior to
placement of the PVC \"stacks\" on top. 149

2\. Transportation of the prefabricated units (top) and units at the
staging area at the west and of the old Bahia Honda Bridge (bottom). 150

3\. Underwater views of the mid-depth prefabricated unit about 90 days
after placement. 151

4\. Deliberate placement of a mid-depth prefabricated unit in June, 1988
(top) and an underwater view of a low profile shallow prefabricated unit
(bottom). 153

5\. Oblique aerial photographs of the shallow prefabricated units (SAR),
the shallow natural reef (SNR), the mid-depth prefabricated units MAR),
and the mid-depth natural reef (MNR). The top photo was taken from about
185 m (600\') altitude with a view to the south. The bottom photo is
from about 90 m (300\') altitude with a view to the west. 154

6\. Underwater view of the shallow natural reef including a school of
juvenile tomtate grunts (*Haemulon aurolineatum*) feeding in the water
column (top), and the mid-depth natural reef (bottom). 155

7\. Underwater views of the deep natural reef and a school of gray
snapper (*Lutjanus griseus*). 156

8\. Steel girders of the Bahia Honda artificial reef being removed from
the old Bahia Honda bridge in 1985 (top) 157

9\. Underwater views of octocorals and a school of mixed grunts
(*Haemulon* *sciurus* and *H. plumieri*) at the American Shoal bridge
rubble reef. 158

10\. Underwater views of PVC and concrete surfaces of a mid-depth
prefabricated unit 3 months (top) and 17 months (bottom) after
placement. 159

11\. Underwater view of a mid-water prefabricated unit 17 months after
placement (top) with browsing gray angelfish (*Pomacanthus arcuatus*).
The bottom photo is of the lower concrete and PVC edge of a deep
prefabricated unit 17 months after placement. 160

12\. Aggregation of yellowtail snapper (*Ocyurus chrysurus*) over a
mid-depth prefabricated unit (top) and aggregation of doctorfish
(*Acanthurus chirurgus*), ocean surgeon (*A. bahianus*), and hogfish
(*Lachnolaimus maximus*) near a mid-depth unit (bottom) 17 months after
placement. 161

13\. Underwater view of a fish trap containing black grouper
(*Mycteroperca* *bonaci*), gray snapper (*Lutjanus griseus*), and gray
angelfish (*Pomacanthus* *arcuatus*) photographed in the study area. 162

ABBREVIATIONS

SAR - Shallow prefabricated unit

SARC - Shallow prefabricated units combined

SNR - Shallow natural reef

MAR - Mid-depth prefabricated unit

MARC - Mid-depth prefabricated units combined

MNR - Mid-depth natural reef

DAR - Deep prefabricated unit

DARC - Deep prefabricated units combined

DNR - Deep natural reef

BH - Bahia Honda bridge rubble reef

AS - American Shoal bridge rubble reef

HAWKC - BR and MIS combined

N - Number of samples

PREFACE

\[PREPARED IN 2005\]

There are a significant number of documents and data related to the
marine environment of South Florida that have never been published, and
are thus not used by scientific community and academia. These documents
and data are important because they can help characterize the state of
the coastal environment in the past, and thus are essential when
evaluating the current state of degradation and setting restoration
goals. Due to the nature of the paper and electronic media on which they
exist, and in some cases the conditions in which they are housed, the
data and documents are in jeopardy of being irretrievably lost. These
materials cannot be located using electronic and manual bibliographic
searches because they have not been catalogued or archived in libraries.

The purpose of the Coastal and Estuarine Data Document Archeology and
Rescue (CEDAR) for South Florida is to collect unpublished data and
documents on the South Florida coastal and estuarine ecosystem; convert
and restore information judged valuable to the South Florida restoration
effort into electronic and printed form, and distribute it
electronically to the scientific community, academia and the public.
\"Data Archaeology\" is used to describe the process of seeking out,
restoring, evaluating, correcting, and interpreting historical data
sets. \"Data Rescue\" refers to the effort to save data at risk of being
lost to the science community.

NOAA/National Ocean Service/National Centers for Coastal Ocean Science
(NCCOS) is not responsible for the accuracy of the findings or the
quality of the data in "rescued" documents.

**THE USE OF LARGE ARTIFICIAL REEFS TO ENHANCE FISH POPULATIONS**

**AT DIFFERENT DEPTHS IN THE FLORIDA KEYS**

Curtis R. Kruer[^1] and Laura O. Causey[^2]

Florida Keys Artificial Reef Association, Inc.

P.O. Box 917

Big Pine Key, FL

Abstract \[PREPARED IN 2005\]

> This study showed that large prefabricated units and concrete rubble
> patch reefs, placed as artificial marine habitats on sand bottom,
> greatly enhance the abundance, diversity, and biomass of fish in an
> area. Densities of individuals and biomass were found considerably
> higher at artificial reefs than at nearby, natural, bank reefs, a
> result consistent with other studies. Location, depth, and vertical
> profile are important factors determining fish assemblages at
> artificial habitats in the Keys. Fishes were both produced at
> artificial reefs and attracted from the surrounding area. Fish
> assemblages at the Hawk Channel artificial reefs were considerably
> different from those on the offshore reef tract, particularly in terms
> of dominant species. Rescue of the original 1992 work in 2005 was
> funded by the South Florida Ecosystem Restoration Prediction and
> Modeling Program.

1\. Introduction. Introduction;

The use of artificial reefs as fishing sites is well established in the
Florida Keys. Early residents knew that wrecks, sunk accidentally or
deliberately, often produced concentrations of fish. In recent years,
artificial \"patch reefs\" have been created with large concrete slabs,
boulders and rubble from bridge removal projects, and large steel
vessels have been intentionally sunk. The main purpose of artificial
reef construction is to enhance, supplement, or mimic natural reef
habitats by providing relief on flat, featureless ocean bottom (Seaman
and Sprague, 1991). Artificial reef construction increases habitat
diversity, vertical relief, and \"hard bottom\", creating new fishing
and diving opportunities.

Florida\'s coral reef ecosystem supports extensive recreational and
commercial fisheries for species dependent on complex reef habitats
during some all stages of their life cycles. Of particular importance
are fisheries for snapper, grouper, grunt, and porgy on natural hard
bottom and reef habitats. Mid-water species such as mackerel, jack,
cobia, and barracuda are often caught near habitats with high vertical
relief. The marine life industry collects reef fishes and invertebrates
for aquariums; fishes targeted include angelfish, butterflyfish,
damselfish, wrasse, parrotfish and goby. Expansion of boating and
fishing activity in South Florida and much improved technology have
increased pressure on most reef species with fishery value.

Fishing and diving industries in the Keys have benefited greatly from
the sinking of large vessels and rubble reefs. The marine life industry
collects live specimens on rubble reefs. Artificial habitats can reduce
user conflicts, increase fishing and boating efficiency, make fishing
and diving more predictable, increase public access to fishery
resources, and enhance fish abundance through attraction and production
(Bohnsack, 1989). Milon (1991) reported that about 28% of anglers and
14% of divers use artificial habitats in the Dade County (Miami),
Florida area.

As habitat for fish, artificial reefs provide food resources, shelter
from predation, and sites for orientation and reproduction (Bohnsack and
Sutherland, 1985). Shulman (1984) concluded that shelter from predation
may be more important to fish recruitment than food availability, but
some species may be limited more by supply of larval recruits (Bohnsack,
1990). Observations of higher fish densities at artificial reefs than at
nearby natural reefs are common, although community structures are
usually similar (Bohnsack, 1990). Research has shown that, although the
fish assemblages vary at different artificial reefs because of different
physical conditions, increasing habitat complexity increases abundance
and diversity (Alevizon and Gorham, 1989; Bohnsack and Sutherland, 1985;
Bohnsack *et al.,* 1989; Bohnsack, 1990).

Like many other non-profit and governmental artificial reef programs
around the Gulf of Mexico, the Florida Keys Artificial Reef Association
(FKARA), organized in 1980, has functioned mainly as an opportunistic
builder of reefs when suitable material or vessels were available. From
1981 to 1987, FKARA supervised the placement of 35,000 tons of bridge
rubble at six permitted sites, and the sinking of five vessels from
187\' to 327\' long from Key Largo to Key West (FKARA, 1990). All
materials were placed onto sandy bottoms. Although fish surveys have
been conducted on several of these shallower rubble reef sites for
years, available information is limited to relative abundance, general
patterns of succession, and, to some degree, recruitment.

The use of prefabricated reef structures in the eastern United States is
not common, but as the uses of artificial reefs evolve from exploitation
towards resource conservation and management, assessment of their value
is taking place (Seaman *et al.,* 1989). In 1987 and 1988, FKARA
obtained donated materials, labor, and work space, funds through fund
raising, and a state grant for transportation that allowed construction
and placement of seven prefabricated concrete units of two different
designs. The largest (27 m2 bottom area, 5 m high with PVC, 7 mt) are
believed to be the largest prefabricated units ever used in south
Florida as artificial marine habitats.

A NOAA grant through the National Marine Fisheries Service (NMFS),
Marine Fisheries Initiative (MARFIN) program funded the two-year
monitoring project that followed unit placement in June of 1988 and the
preparation of this descriptive report. The purpose of this study was to
evaluate the potential for fishery enhancement of placing large
prefabricated units and concrete rubble in different depths and
locations off the Lower Florida Keys. The project was designed to
produce useful information on the responses of fish to the introduction
of specific types and profiles of large structures. Examined were
production potential, locational differences, fishery value, and
economics of two different types of artificial reef construction
projects. Censusing adjacent natural bank reefs using standard methods
allowed comparisons of community structure. Fishes were censused on 15
bridge rubble \"patch reefs\" placed from 1983 to 1987 at two locations
in Hawk Channel for additional comparisons. The study\'s original
objectives were:

> 1\. Quantify the species composition, biomass and seasonality of
> fishes attracted and produced on large fabricated artificial habitats
> over a 24-month period.
>
> 2\. Compare the colonization and community structure of reef fishes on
> the fabricated habitats to nearby natural reefs.
>
> 3\. Evaluate the effects of reef sitting at different water depths on
> species composition, recruitment, and biomass.
>
> 4\. Separate fish communities into trophic levels to assess location
> of food source (e.g. water column, surrounding bottom, structure
> fouling community, etc.)
>
> 5\. Through standard photographic techniques, document and quantify
> plant and invertebrate fouling communities as a function of substrate
> and water depth.
>
> 6\. Determine if large, fabricated habitats can provide significant
> fishing opportunities.
>
> 7\. Evaluate the economics of construction, transportation, and
> placement of artificial habitats to enhance fishery resources and
> fishing opportunities.

Understanding how much artificial reefs increase fish numbers and
biomass is important to wise fishery management and to the proper
construction and deployment of artificial reefs (Bohnsack, 1989). Basic
knowledge of the results of reef building is critical to measure their
value in a region as unique and significant as the Florida Keys, where
future efforts could include additional concrete rubble reefs, clean
steel vessels, and prefabricated concrete units. How artificial reefs
should be used in a comprehensive fisheries (and people) management
program in the Florida Keys National Marine Sanctuary will be resolved
only through continued accumulation of ecological information on fish
assemblages associated with reef habitats and documentation of various
human uses. The use of structured, consistent methods for assessment of
artificial habitats and the collection of long term population data on
natural reef communities will facilitate important management decisions.
As well, the ability to provide alternative fishing and diving sites
through the creation of productive artificial reefs could assist in the
management of people in one of the most popular fishing and diving
locations in the United States and the world.

2\. Methods . Methods ;

2.1. Overview .1. Overview ;

Project design was based on recommendations of Bohnsack and Sutherland
(1985) in regard to the need for experimentation with large,
inexpensive, long lasting, easily handled, and easily transportable,
artificial reefs. Efforts were made to collect quantitative data on the
short and long-term physical, biological, and economic aspects of
artificial reef projects as well as to establish baselines for future
comparisons.

Seven prefabricated structures were placed in 1988 in three depths on
the Florida reef tract near Big Pine Shoal. Of these, three low profile
concrete units were placed in the shallowest depth (7 m), and two high
profile concrete and PVC units were placed at mid-depth (14 m) and deep
(24 m) sites. Fish assemblages on the units and nearby natural reefs
were censused for two years following unit placement. Rubble reefs,
placed from 1983 to 1987, were censused in mid 1989. Assemblages were
compared by species composition, frequency-of-occurrence, abundance, and
biomass. Species at each artificial reef were classified as settler or
colonizer species for indications of production potential. Fishery
values, if any, and trophic group were determined for each species.

2.2. Artificial Reef Construction and Placement .2. Artificial Reef
Construction and Placement ;

The prefabricated units were designed by FKARA in collaboration with a
structural engineer and built at a construction yard on Big Pine Key in
late 1987 and early 1988. Pre stressed concrete (6,000 PSI) beams (15 cm
x 20 cm) were used for diagonal and vertical members of the high profile
units and for horizontal beams in the low units (Figs. 1 and 2, Plate
1). The units were structurally unified with tied, reinforcing steel in
the poured concrete (4,000 PSI) base and upper beams. They are designed
to last indefinitely and survive severe storms. Grove *et al.* (1991)
note that shapes and dimensions of fabricated reefs with desirable
structural integrity and durability are best developed based on
knowledge of the \"environmental loading" anticipated and the strength
of the materials used. Important structural characteristics for
artificial habitats include profile, shadow, vertical relief, surface
area, substrate, holes, voids, and interstices that provide cover for
fishes (Bohnsack, 1990). Japanese experiences using large prefabricated
reefs to enhance fish populations suggest that maximum horizontal spread
profile should be emphasized and that vertical profile probably need not
be more than about 5 m high (Grove *et al.,* 1991).

The four high profile units were fabricated with identical square (5.15
m x 5.15 m) bases (Plate 1) to prevent toppling and open sides to
minimize effects of wave surge during storms. The wide base beams were
designed to minimize sinking into sand substrates. The concrete portion
of the structure was 2.8 m high. Total height, including the PVC
\"stacks\", ranged from 4.6 to 5.4 m (Fig. 1, Plates 2 and 3). The top
PVC pieces were seated in a PVC base embedded in the poured concrete top
beam and were held in place by large galvanized pins in holes drilled
through both pieces. Each high unit covered about 27 m2 of bottom, had a
volume of 40 m3, a surface area of about 66 m2 (43 m2 concrete and 23 m2
PVC), and weighed approximately 7,300 kg. Structural variation between
high units was limited to the eight vertical concrete end pieces (0.9 to
2.0 m tall) and the PVC tubes, thick walled (15 cm diameter, 0.7 to 2.5
m tall) at the top and thin walled at the bottom of the units (11 cm
diameter, 0.1 to 0.4 m tall). High units had 5-cm diameter holes drilled
in all top PVC pieces and smaller holes drilled in most bottom PVC
pieces. Upper surfaces of the pre stressed beams were rough, while the
surface of poured concrete was smooth. Most pre stressed beams had
lengths of 0.5-cm diameter steel wire attached by 5-cm steel pegs along
the upright edge (Plate 1), further diversifying the structures\'
surfaces. Bohnsack (1990) reports that the surface of material used can
influence food availability through differences in fouling community
development.

Three low profile units were created by fabricating two separate
table-like structures (3.1 m long and 7.0 m long) and placing the
shortest structure over the other (Fig. 2, Plate 4). Pre stressed beams
were used for cross members, and formed and poured concrete with
reinforcing steel was used to tie beams together on each end and to form
the legs. The three structures had nearly identical dimensions. The
horizontal portions of the structures were elevated from 0.5 m to 1.2 m
above the bottom. The upright surfaces of the pre stressed beams were
rough and included a strip of steel wire on small pegs as on high
profile units. Loops of reinforcing steel were placed in the top of the
poured concrete as lifting rings. Each unit covered about 29 m2 of
bottom, had a volume of 20.4 m3, and weighed about 2,300 kg (2
sections). One small unit (SAR3) had two flat concrete plates installed
on the upper surface to hold inserts of several surfaces.

In June 1988, the units were transported via US Highway 1 to a staging
area at the southwest end of the old Bahia Honda Bridge east of Big Pine
Key (Plate 2). A barge was used to transport the units offshore to the
permitted sites where they were carefully placed with the assistance of
divers on top of markers set in the bottom (Plate 4). Two high profile
units were placed at 14 m depth on June 25, 1988, 50 m apart and 50 m
south of a natural linear bank reef. The other two high units were
placed at 24 m depth on June 26 and 27, 50 m apart and 50 m north of the
natural deep reef. On June 27, the three low units were placed at 7 m
depth, 50 m apart and 50 m from a shallow natural bank reef. Mid-depth
and deep units were placed perpendicular to the prevailing east-west
orientation of current flow. Stakes of reinforcing steel were driven
(September 1988) into the bottom 76 cm off the corners of all except one
deep unit to allow detection of any unit movement.

2.3. Site Conditions .3. Site Conditions ;

The area chosen for placement of the units is a north-south cross
section of the Florida reef tract at latitude 24° 34\' N and longitude
81° 20\' W, about 8 to 9 km south of Big Pine Key and about 7.5 km east
of Looe Key Reef (Figs. 3 - 5). The area is in the blue water zone of
the coral reef ecosystem - the outer reef slope, influenced more by the
warm offshore Florida Current than by the seasonally cooler, green
waters of the Gulf of Mexico. Gilbert (1974) notes that the richness of
the Florida Keys fish fauna is due in large part to the mixing of
continental (green water) and insular (blue water) fish faunas

Mid-depth and deep units were placed onto open, sandy bottom while the
shallow (7 m) units were placed on sandy bottom with nearby patches of
turtle grass (*Thalassia testudinum*) (Fig. 5, Plate 5). Mid-depth units
were placed on a sandy plain with low, flat, relict rock within about 15
m of the west side of the westernmost unit (MAR2, Plate 5). The natural
bank reefs at shallow and deep depths were seaward (south) of the units;
at mid-depth, the natural reef was landward (north) of the units.

Currents on the reef tract were typically mild and variable in
direction; the strongest were on the deep reef, nearest to deep water
and the Florida Current. Winds and seas were usually from the southeast,
except when fall and winter colds fronts produced strong northerly
winds. Water temperature ranged from 22.0 to 30.5 °C (Table 1). Most
temperature measurements were made on the bottom with a hand-held
thermometer; a few were obtained from the Florida Institute of
Oceanography data bank of surface water temperatures at Sombrero Reef, a
few miles to the east. Visibility was affected by strong winds, the
Florida Current, and tides, and varied from 7 to 18 m during census
work. Visibility was lowest on the deep reefs where stratification often
occurs; producing clear, warm, blue water on the surface and \"dirty\",
often cooler water, near the bottom.

The shallow (6 to 8 m) natural reef censused was about 50 m wide and 150
m long (Fig, 5, Plates 5 and 6). This reef was an isolated section of
linear bank reef (Jaap, 1984; Voss, 1988) that extended a considerable
distance to the east. Overall relief was about 2 m with greatest habitat
complexity on the slope along the north edge and on an elevated section
to the west. Relief of individual rock outcrops, large vase sponges, and
large octocorals was up to 1 m. Soft corals included *Pseudopterogorgia*
sp., *Pseudoplexaura* sp., *Gorgonia* sp. and major stony corals
included *Siderastrea siderea*, *Stephanocoenia michelinii*, *Porites
astreoides*, *P. porites*, *Agaricia agaricites*, *Dichocoenia
stellaris*, *Montastraea* *cavernosa*, and *Millepora* *alcicornis*. Of
all the natural reefs censused, only this area had associated beds of
seagrass.

The mid-depth (10 to 12 m) natural reef censused was about 50 m wide and
part of an elongated (east-west) bank reef (Fig. 5). The homogeneous
reef sloped about 20 to 30 degrees seaward, with overall relief of about
2 m, and well developed sand channels to about 0.7 m deep (Plate 5).
Maximum vertical relief provided by octocorals, hard corals, rock, and
sponges was about 1.4 m (Plate 6). This reef consisted of a larger
proportion of hard corals than the shallow natural reef, including
*Porites astreoides, Montastraea annularis, Millepora alcicornis,*
*Siderastrea radians*, *Dichocoenia stokesii, Colcophyllia natans*,
*Oculina* *diffusa*, *Manicina* *areolata*, and *Meandrina meandrites*.

The deep natural reef was censused at a depth of 26 to 31 m on a steep,
seaward facing slope of about 40 to 60 degrees. Immediately south of the
reef began the expanse of open sand that descends offshore into deeper
waters of the Straits of Florida. At about 15 to 20 m wide, this linear
reef was relatively homogeneous, smaller than the shallow and mid-depth
reefs censused and somewhat discontinuous beyond the census area to the
east and west. This relict reef consisted of large, eroded, rocky areas
with relief up to 1.2 m (Plate 7). Exposed rock was encrusted with
sponges, octocorals, bryozoans, and hard corals including
*Stephanocoenia michelinii, Agaricia agaricites, Montastraea cavernosa*,
and *Siderastrea siderea*.

Two additional study sites were the Bahia Honda and American Shoal
rubble reefs in Hawk Channel (Fig. 4) constructed from 1983 to 1987 by
placing large concrete boulders, concrete deck slabs and heavy steel
from local bridge removal projects on sand bottom. The Bahia Honda site
includes large steel girders from removal of the old Bahia Honda Channel
bridge (Plate 8). The location in little-studied Hawk Channel (to 14 m
depth), which lies between the reef tract and the island chain,
influences physical parameters, particularly water clarity, and probably
minimum water temperature. Proximity to tidal channels connecting to the
Gulf of Mexico and the depressional nature of the area results in
frequent stratification of the water column. These sites appear to be
influenced more by green waters of the Gulf of Mexico than by the
Florida Straits.

The Bahia Honda rubble site, in 9 to 10 m depth on the north edge of
Hawk Channel about 4.5 km offshore from Bahia Honda Channel (Fig. 4), is
composed of 19 \"patch reefs\" placed in 1985 and 1987 containing a
total of about 6,000 mt of material (Plate 8). Averaging about 150 m2 in
area, but with considerable size range, the patches are separated by
about 20 to 70 m and are scattered over about 2 ha. Schroeder (1987)
reported that a grouping of several small reefs produces higher density
and higher total number of recruits than one large reef. Patches vary
somewhat in combinations of materials (concrete boulders, slabs, and
rubble; steel girders, pipe and pipe hangars), size, vertical profile,
and open space within the patch. The patches are just seaward of deep
beds of predominantly turtle grass and shoalgrass (*Halodule wrightii*)
that extend offshore to the 9-m depth contour. Vertical relief on the
patches ranged to about 2.5 m. In the years between placement and the
1989 censuses, a variety of sponges and large octocorals (to 58 cm tall)
have flourished on hard surfaces, along with some stony corals.

The American Shoal rubble reef consists of four patch reefs, averaging
about 450 m2, placed from 1983 to 1987 on sand bottom at a depth of 11
to 12 m on the south (seaward) edge of Hawk Channel (Fig. 4). Patches
were constructed by carefully placing a total of 3,800 mt of large
concrete slabs, boulders, and steel pipe from local bridge removal
projects. Vertical relief ranged to about 2.5 m. The four patches vary
somewhat in materials and profile: patch 1 is mostly large boulders and
slabs with open space between many pieces; patch 2 is both large and
small boulders in a large mound with some pipe; patch 3 is high profile
large boulders, slabs and pipe; patch 4 is a mound of boulders and
slabs. By 1989, octocorals had reached a height of 50 cm on the oldest
material, adding appreciably to the structural complexity of the site
(Plate 9). Various sponges and small stony corals were also present.

2.4. Sampling .4. Sampling ;

2.4.1. Prefabricated Units .4.1. Prefabricated Units ;

Divers listed and counted all fishes at prefabricated units and
estimated the range of fork length of each species using standard visual
census techniques (Bohnsack and Talbot, 1980; Bohnsack *et al.,* 1989).
Large fish were recorded first from a distance, then the unit was
inspected closely for small and cryptic species. A zone about 5 m wide
around each unit was included to insure all fishes associated with the
structure were counted. A second diver recorded cryptic and unusual
fishes allowing comparisons and creation of accurate census records. The
units were censused on June 30, 1988 (mid-depth units also on June 27),
after placement, then monthly for the next three months, and every other
month thereafter until June 1990.

2.4.2. Natural and Rubble Reefs .4.2. Natural and Rubble Reefs ;

On natural reefs and bridge rubble reefs where total counts were not
possible, a stationary sampling method developed by Bohnsack and
Bannerot (1986), was used to visually sample the community structure of
highly diverse and abundant reef fish populations. Stationary censuses
were also taken on sand bottom at the two mid-depth sites prior to unit
deployment to allow comparison of changes as a result of unit placement.
A major value of the stationary sampling method is that quantitative
data are collected simultaneously on species composition, abundance,
frequency-of-occurrence, and lengths of all visually detectable species.
This method, considered extremely effective for censuring reef fish and
providing indices of abundance for comparative purposes, is simple,
fast, objective, and repeatable (Bohnsack and Bannerot, 1986). Sale
(1991) concludes that stationary visual censuses can have definite
advantages over other census methods. As in other census methods,
documentation of many crevice dwelling and cryptic species is poor.
Alevizon (1990) assesses various reef fish census methods used in south
Florida and reminds us that at night reef fish communities differ
substantially from those observed during the day.

Two divers went to different regions of a natural or rubble reef to be
censused, and each established an initial census area (177 m2 ) using a
7.5-m anchored rope to delineate the sample circle\'s radius. Stationary
at the center of the circle, the divers listed all species observed in 5
minutes within an imaginary cylinder extending from the bottom towards
the water\'s surface. After 5 minutes, beginning at the bottom of the
list, all individuals of each species within the sample area were
counted and the range of fork lengths estimated using 40 cm rulers at
the ends of poles carried by the divers to reduce effects of
magnification. Fast moving species, such as jacks and mackerels, were
counted during the initial 5 minutes. The percentage of sand and
rock/coral surface in the sample area was recorded along with water
depth, temperature, and visibility. After the initial census, each diver
traveled to a second census site based on a predetermined, randomly
derived list of compass headings and distances, and the process was
repeated. Distance traveled between censuses was measured by swim kicks
and was adequate to preclude overlap. Divers worked in different regions
of the reef to avoid interference with the other\'s counts. At most,
three censuses were conducted during a single dive on shallow and
mid-depth reefs and two censuses on the deep reef. Project design
required eight stationary samples from each the mid-depth and deep
natural reefs and 12 from the shallow natural reef during months when
the adjacent units were counted. All regions of the natural bank reefs
near the units were censused during the two years of sampling. To insure
consistency, the authors conducted all censuses.

The bridge rubble reefs in Hawk Channel were censused from June to
August, 1989. A 7.5-meter radius visual census area was established on
different patches after they were located with land ranges and a depth
recorder. At the American Shoal site, all samples were collected on the
three westernmost patches (numbers 1 - 3). At the Bahia Honda site,
several censuses were made on each of the largest patches (numbers 1 and
2) which include large, piled steel girders; the remainder were made on
about 10 other patches randomly sampled. Poor visibility (\<7 m)
precluded censuses on several occasions at both natural and rubble
reefs.

2.5. Analysis .5. Analysis ;

Census data from prefabricated units, natural reefs, and bridge rubble
reefs were entered into a data entry template for \"Reef Fish Visual
Censusing Samples\" provided on Lotus 1-2-3 by the Southeast Fisheries
Center of the NOAA National Marine Fisheries Service (NMFS) in Miami,
Florida (D. Harper, pers. comm., 1989). Multiple samples were processed
into a flat data file from which a summary analysis of samples from
different locations was performed by the NMFS program. Mean length was
determined for each species in each sample from the range of lengths
recorded in the field. Total biomass was calculated for each species at
all artificial reefs and the deep natural reef using overall mean
lengths and length to weight formulas in Bohnsack and Harper (1988).
Density was estimated for comparative purposes by dividing the total
number of fishes censused at a site by the area censused. Similarity
between fish assemblages at two reefs was determined by comparing
species shared to the total number of species and by comparing the 15
most frequent, abundant, and heaviest species at the two sites.

To determine which species have the potential for being produced by
these types of artificial habitats, reef fishes were separated into
settlers and colonizers using a modification of the following
definitions by Bohnsack *et al.* (1989):

> \"[Settlers]{.underline} are defined as species that arrived at the
> artificial reef directly from the plankton as larvae.
> [Colonizers]{.underline} are defined as species that arrive at a reef
> as juveniles or adults after apparently settling elsewhere and then
> swimming to the artificial reef.\"

Production and attraction at artificial reefs are not mutually exclusive
and actually occur on a gradient or continuum depending on reef type and
location (Bohnsack, 1989). Settler species, as defined here, are species
of which at least a single young juvenile was recorded, a result of
either settling directly from the plankton or moving to the artificial
habitat a short time after settling in nearby sand or seagrass. Settler
species have documented potential to be supported by these types of
artificial habitats at a very early life stage (at least for a short
period), benefitting by the food and shelter resources provided.
Determination of a settler species was based on the minimum size
recorded at a site, juvenile coloration, and known biology of individual
species. Questionable individuals were listed as settlers. Colonizer
species at a site were those never observed at a young juvenile size,
and included visitors and transients. Bohnsack *et al.* (1991) note that
many reef fishes initially use an intermediate habitat (e.g. sand
plains, rubble zones, seagrass beds) prior to using reef habitats.

Fishes at the mid-depth and deep units, the deep natural reef, and the
Bahia Honda rubble reefs were separated into trophic categories based on
designations in Bohnsack *et al.* (1989) for comparison and assessment
of food source.

An economic fishery value classification (commercial, recreational,
marine life) was assigned to each species based on lists in Bohnsack *et
al.* (1989), marine life industry lists contained in Florida
Administrative Code Chap. 46-42.001 (Marine Life), and commercial
experience of both investigators in the collecting and wholesale of
marine life throughout Florida.

2.6. Foulinq Community Photography .6. Foulinq Community Photography ;

Photography was conducted on a quarterly basis from September 1988 to
August 1990. Six points, marked either with nails driven into the
concrete or located by measured distances, were established in the same
locations on the concrete surfaces of each of the low units (Fig. 6).
Six points were established on each side (east and west) of each of the
high units (Fig. 6 ) resulting quarterly in 12 images for each unit. A
Nikonos V camera with a 28-mm lens, SB-103 strobe, and close-up unit
with a frame measuring 12.8 cm x 18.4 (236 cm2) cm was used with
Fujichrome 50 color transparency film. Routine underwater photography of
the units was conducted as well.

3\. Results . Results ;

Four hundred eleven visual fish censuses were conducted in 23 different
months from June 1988 to June 1990 (Table 1); a total of 105,405
individuals of 179 species (Table 2) in 44 families (Table 3) was
recorded from all sites. Although fishes not identified to species level
represented 10% of those listed, they were minor and infrequent
contributors to the total number of individuals except for unidentified
juvenile grunts and scad in local abundance.

In 104 counts on the seven prefabricated units, 9,515 individuals (978
kg) of 108 species in 33 families were recorded (Table 4). Combining all
50 samples from bridge rubble reefs showed 43,289 fishes (2,345 kg) of
103 species in 34 families (Table 5). Two hundred fifty-seven censuses
on the three natural reefs showed 52,601 individuals of 156 species in
39 families (Table 6). By comparison, Bohnsack *et al.* (1987), using
two census methods at Looe Key Reef, reported 188 species in 48 families
from 10 habitat zones (0 to 12 m depth). At Looe Key Reef, known for its
high spur and groove formations, 66 species of grunts, damselfishes,
wrasses, sea basses, and parrotfishes made up 35% of total species. Here
these families represented 66 species, 36% of the total, with seven
members not identified to species level (Table 3).

Both numbers of species (Fig. 7) and relative fish density (Fig. 8) were
comparable at prefabricated units in the same depth. Highest species
richness and abundance were at the mid-depth units. The numbers of
species were similar at the different natural reefs, but density
appeared to increase with greater depth. Fish density ranged from a low
of 0.9 inds./m2 at the shallow natural reef to 5.9/m2 at the Bahia Honda
site. Of the Hawk Channel rubble reefs, Bahia Honda had the more diverse
and abundant fish assemblage. Biomass density at artificial reefs ranged
from a low of 199 g/m2 at the Bahia Honda site to a high of 483 g/m2 at
the deep units. The deep natural reef, the only natural reef for which
biomass was reviewed, showed 72 g/m2.

The prefabricated units proved to be very stable on the bottom even
during high seas (9 - 11 feet) resulting from the passage of several
tropical storms and severe cold fronts during the study period.
Monitoring at the end of two years revealed that movement was limited to
a few centimeters at the westernmost mid-depth unit (MAR2), the other
units appeared not to move at all. Several of the top PVC stacks were
removed during the study, possibly due to vandalism.

3.1. Shallow reefs.1. Shallow reefs;

3.1.1. Prefabricated Units.1.1. Prefabricated Units;

Fourteen counts were made on each of the three low profile shallow units
from June 1988 to June 1990 (Table 1); summaries are in Table 7 (SAR1),
Table 8 (SAR2), and Table 9 (SAR3). All units were censused during the
same dive. The number of species recorded at a unit ranged from 38
(SAR1) to 45 (SAR3), and total individuals ranged from 638 (SAR1) to 683
(SAR3). Maximums of 19 species and 89 individuals were recorded in a
single unit count. Combining all counts of the three shallow units
revealed 67 species and 2,002 individuals (Table 10).

The average number of species per census of each unit ranged from 9.6 to
12.3, and the average number of fishes per census ranged from 45.6 to
48.8 (Fig. 9). Trends in numbers of species (Fig. 10) and individuals
(Fig. 11) showed rapid increases the first few months, declines the
first winter, and increases again the following June. The average number
of species increased considerably by the second summer, but the number
of individuals increased only slightly and peaked in October. Similarity
of species between units ranged 40% (SAR2 and SAR3) to 53% (SAR1 and
SAR2) (Table 11). Twenty-two species (33%) were recorded at all three
units.

3.1.2. Natural Reef.1.2. Natural Reef;

One hundred eleven stationary visual samples were collected at the
shallow (6 to 8 m) natural reef in ten different months from July 1988
to April 1990 (Table 1). Combining all samples showed 107 species and
17,038 total individuals (Table 12). Maximums of 30 species and 335
individuals were recorded in a single census. The number of species,
104, was the lowest of the natural reefs censused (Fig. 7), and fish
density (0.9/ m2) the lowest of all reefs, including the units (Fig. 8).

3.2. Mid-Depth Reefs.2. Mid-Depth Reefs;

3.2.1. Prefabricated Units.2.1. Prefabricated Units;

Sixteen counts were conducted on each of the two high profile mid-depth
units from June, 1988 to June, 1990 (Table 1); summaries are at Table 13
(MAR1) and Table 14 (MAR2). Both units were censused on the same dive.
MAR1 showed totals of 55 species and 2,395 individuals, MAR2 had 58
species and 2,036 individuals. Maximums of 25 species and 873
individuals (800 juvenile grunts) were recorded in a single unit count.
Combining counts at both units showed 73 species, 4,421 individuals
(Table 15), and an estimated density of 4.2 inds./m2 when the 800 grunts
are excluded (Fig 8). Total biomass was 335 kg (738 lbs.).

The mid-depth units had the highest mean number of species per census
(16.5) and the most individuals per sample (113.5) of all units (Fig.
9). An additional count at each MAR unit only several days after
placement, and not made at other units, was included in the data base
and slightly lowered mean values. The mean number of species in the
second year was 19.3. The number of individuals per sample was more than
double that at the shallow units and about two-thirds greater than at
the deep units. The average number of species per census was about the
same for each of the two units, 16 to 17 species, but the average number
of individuals was about 27% higher at MAR2 (excluding 800 grunts at
MAR1) (Fig. 9). The location of MAR2, within about 15 m of an area of
flat, hard bottom with some sponges and gorgonians extending from the
bank reef may have accelerated colonization at this unit.

Trends in the fish populations on the MAR units were similar the first
year but varied somewhat the second (Figs. 12 and 13). Little
seasonality was seen in the bimonthly number of censused species, and
near average numbers was reached a few months after placement. The
overall number of fishes peaked the first fall, declined substantially
the first winter, and increased the second year.

June, 1989 was a month of considerable difference between the units,
particularly in grunts. MAR1 (14 total species, 48 inds.) had a single
cottonwick grunt (14 cm) while MAR2 (20 species and 270 inds.) showed
211 grunts of four species (2 - 10 cm). Small ledges under the base
beams of the units caused by wave surge during windy periods,
contributed to the diversity and abundance of crepuscular and juvenile
bottom dwelling fishes by providing shelter from predators and probably
accounted for these differences. Bohnsack *et al.* (1989) concluded that
fish assemblages were influenced by microhabitat modifications at reefs
including sand chambers opening and closing under concrete modules. The
temporal variation in grunts at the mid-depth units, illustrates the
highly changeable nature of many fish populations. In a census in
August, 1988, 802 grunts (2 - 8 cm long) were recorded, five weeks later
there were only 30 (2 - 8 cm). In October, 1988, 60 tomtates (2 - 8 cm
long) were noted at a unit, 2 days later there were only 5.

The two mid-depth units shared 40 species, 55% of their combined total
(Table 11). Comparison of the 15 most frequent and abundant species on
each unit revealed 72% similarity of frequent species and 67% similarity
of abundant species, the second highest of any comparison after the deep
units (Table 16). Shared of the 15 most frequent species were blue tang,
ocean surgeon, doctorfish, sharpnose puffer, reef butterflyfish,
slippery dick, bluehead wrasse, gray angelfish, hogfish, porkfish,
masked goby, twospot cardinalfish, and yellowtail snapper (Table 17).
Shared of the most abundant were tomtate, bluehead wrasse, yellowtail
snapper, mackerel scad, ocean surgeon, masked goby, blue tang,
yellowhead wrasse, slippery dick, unidentified scad, twospot
cardinalfish, and doctorfish.

In early June, 1988, five stationary censuses taken on the open bottom
before placement of the mid-depth units showed 11 species and 62
individuals (12.4/census), mostly wrasses, bottom dwelling gobies, sand
perch, and sand tilefish. Pre-project density of fishes at these sites
was 0.07/m2. Bohnsack *et al.* (1989) in 98 predeployment and sand
control samples found 27 species and density of 0.09 inds./m2. The
two-year mid-depth unit mean fish density of 4.2/m2 excluding 800
juveniles grunts in one sample, reflects about a 6,000% post-placement
increase in fish density. Including all grunts reflects about a 7,300%
increase.

3.2.2. Natural Reef .2.2. Natural Reef ;

Seventy-eight stationary samples were collected at the mid-depth (10 to
12 m) natural reef in ten different months from September, 1988 to May,
1990 (Table 1). Combining all samples showed 114 species and 17,106
individuals (Table 18). Maximums of 33 species and 2,633 individuals
(2,500 unid. juvenile grunts) were recorded in a single census. The
greatest number of species of all reefs sampled was recorded here, but
density, 1.2 inds./m2, was the second lowest of all sites (Figs. 7 and
8).

3.3. Deep Reefs .3. Deep Reefs ;

3.3.1. Prefabricated Units.3.1. Prefabricated Units;

Fifteen counts were made on each of the two high profile deep units from
June, 1988 to June, 1990 (Table 1). Summaries are at Table 19 (DAR1) and
Table 20 (DAR2). Both units were counted on the same dive. Fifty-three
species and 1,029 individuals were recorded at DAR1 and 57 species and
2,063 individuals (1,000 round scad in one count) at DAR2. Maximums of
23 species and 1,145 individuals were recorded in a single census.
Combining units revealed 69 species and 3,092 individuals (Table 21) and
a density of 2.6 inds./m2 (excluding 1,000 scad) (Fig. 8). Total biomass
was 389 kg (852 lbs.).

The two deep units were similar in mean numbers of species and
individuals, which were greater than the numbers on the shallow units
and less than those on the mid-depth units (Fig. 9). The development of
the fish populations on each of the deep units was similar. The number
of species increased gradually the first year and leveled off thereafter
(Fig. 14). The number of individuals increased gradually most of the
first year with a slight decline the first winter and a variable but
increasing trend thereafter (Fig. 15). The number of fishes was
considerably higher at the end of 24 months than after 12 months.

Comparison of species found on the two deep units showed 59% similarity
with 41 shared species, the highest similarity of all unit comparisons
(Table 11). Comparison of the 15 most frequent and abundant species at
each unit showed 88% and 76% similarity, respectively (Table 16).
Frequent species found at both units were graysby, bluehead wrasse,
hogfish, sharpnose puffer, bicolor damselfish, masked goby, slippery
dick, gray snapper, yellowhead wrasse, yellowtail snapper, twospot
cardinalfish, spotfin butterflyfish, and doctorfish (Table 21a).
Abundant species shared were bluehead wrasse, bicolor damselfish, masked
goby, twospot cardinalfish, gray snapper, yellowtail snapper, yellowhead
wrasse, slippery dick, graysby, sharpnose puffer, doctorfish, spotfin
butterflyfish, and hogfish.

3.3.2. Natural Reef.3.2. Natural Reef;

Sixty-eight stationary surveys were made at the deep (26 to 31 m)
natural reef in ten different months from September, 1988 to May, 1990
(Table 1). Total samples showed 109 species and 18,457 fishes (Table
22). There were maximums of 39 species and 791 individuals in a single
count. The mean density of fishes (1.5/m2) was the highest of all
natural reefs, about 66% higher than the shallow natural reef, and 25%
higher than the mid-depth natural reef (Fig. 8).

3.4. Bahia Honda Rubble Reefs.4. Bahia Honda Rubble Reefs;

Twenty-six stationary censuses were made at the Bahia Honda site from
June to August 1989; 7 on patch reefs created in 1985 and 19 on patches
created in 1987. Of the 19 patch reefs at the site, 13 were sampled.
Water temperature ranged from 27 to 30.5 °C. Visibility, typically poor
on the bottom of Hawk Channel, ranged from about 7 to 12 m during
censuses. Due to irregular edges and the small size of some patches, six
samples included from 25% to 50% sand. The combination of poor
visibility during nearly half of the counts and a high percentage of
open bottom in many samples may have resulted in low abundance and
density estimates for these habitats. Conducting censuses at times of
high visibility would allow total counts to be made on at least the
smaller patches. Sixteen qualitative fish surveys made at the site by
the principal investigator during nine different months July, 1985 to
May, 1989, were reviewed for documentation of juveniles (settlers) of
species recorded here.

Ninety species were recorded at the Bahia Honda reefs representing
27,151 individuals, of which 73% were tomtate grunts with a mean length
of 9 cm (Table 23). Maximums of 32 species and 4,666 individuals were
recorded in a single sample. Fish density was estimated at 5.9 inds./m2,
the highest of all reefs sampled (Fig. 8). Total biomass censused was
915 kg (2,018 lbs.). The Bahia Honda site shared 59 species (57%
similarity) with the American Shoal rubble site (Table 11). Of the 15
most frequent, abundant, and heaviest species at each site, Bahia Honda
and American Shoal shared 30%, 50%, and 50%, respectively (Tables 16 and
34).

Grunts (4.5/m2) of seven species comprised 76% of fishes (Table 23).
Lane and gray snapper totaled 253 individuals, but only 10 yellowtail
snapper were recorded. There were 115 *Mycteroperca* groupers from 6 to
100 cm long and 23 *Epinephelus* groupers to 60 cm, with several species
occurring in most samples. Seventy-six snook (in 30.8% of samples)
averaged 76 cm long, with 35 recorded in a single census.

3.5. American Shoal Bridge Rubble Reefs.5. American Shoal Bridge Rubble
Reefs;

Twenty-four stationary censuses were made in July and August 1989 at
this site. Of the four patch reefs, six counts were made on patch 1
(1983 placement) , 11 at patch 2 (1985), and seven at patch 3 (1987 ).
Water temperature was 30 to 31 °C and visibility poor, usually about 7
to 8 m during censuses, near the minimum required. Ten of the counts
included 25% to 50% sand. As at Bahia Honda, the combination of poor
visibility and a high percentage of sand in some census areas may have
caused an underestimation of the abundance and density of fishes on the
reefs. Eleven fish surveys made by the principal investigator in seven
different months July, 1985 to July, 1988 were reviewed for occurrences
of juveniles (settlers) of species recorded here.

Seventy-two species and 16,138 individual fishes were recorded; 63% were
tomtate with a mean length of 16 cm (Table 24). Thirty-two species were
the most recorded in a single sample and 2,402 the maximum number of
individuals. (See Bahia Honda above for species similarity). Estimated
density of fishes was 3.8 inds./m2, the third highest of all sites
following the Bahia Honda rubble reefs and the mid-depth units (Fig. 8).
Total biomass censused was 1,430 kg (3,153 lbs.).

Six species of grunts, at a density of 3.4/m2, comprised 89% of fishes
censused. Also included were 305 lane and gray snappers, and 34
yellowtail snappers. There were 16 *Mycteroperca* groupers from 6 to 50
cm long and 12 *Epinephelus* groupers. Eight snook (in 25% of samples)
averaged 63 cm long.

3.6. Hawk Channel Rubble Reefs Combined.6. Hawk Channel Rubble Reefs
Combined;

Combining the two Hawk Channel sites (Tables 5 and 25) showed 103
species, nearly 50% more species than any set of units but slightly
fewer than the 108 species from all units combined. Species on rubble
reefs in Hawk Channel were compared to those on the mid-depth natural
reef at about the same depth. Three-quarters of rubble reef species were
also found on the natural reef, corresponding to the percentage of
similarity found between units and adjacent natural reefs (Table 11).
However, there was a higher percentage of species shared (55%), more
artificial reef species compared to total species (74%), and a higher
percentage of natural reef species found at the rubble reefs (68%). The
structural complexity of the rubble reefs that resembles natural reefs
may account for higher levels of similarity with MNR. Comparison of the
mid-depth units to the Hawk Channel reefs showed similarity consistent
with comparisons of each set of units to the adjacent natural reefs
(Table 11).

Comparison of the 15 most frequent and abundant species at Hawk Channel
sites to those at natural reefs showed greatest similarity (33% and 25%)
with the shallow natural reef, the closest natural reef censused, and
least with the deep natural reef (7% and 20%) (Table 16). Comparisons
with the mid-depth natural reef, showed only 20% similarity in most
frequent species and 15% similarity in most abundant (Table 35). Of the
9 most frequent species in Hawk Channel, only striped parrotfish and
cocoa damselfish were recorded in the top 15 species by frequency at the
mid-depth natural reef (Table 35). Comparing the 15 most abundant
species showed only tomtate and striped parrotfish shared with MNR,
along with unidentified grunts and unidentified scad. Although overall
species lists of the Hawk Channel sites and the mid-depth natural reef
were somewhat alike, the substantially different physical conditions
between the two areas appear to result in less similarity of dominant
species.

4\. Discussion of Objectives. Discussion of Objectives;

4.1. Objective 1. Quantify the species composition, biomass, and
seasonality of fishes attracted and produced on large fabricated
artificial habitats over a 24 month period. .1. Objective 1. Quantify
the species composition, biomass, and seasonality of fishes attracted
and produced on large fabricated artificial habitats over a 24 month
period. ;

On several occasions at the shallow and mid-depth units mixed schools of
blue tang, ocean surgeon, doctorfish, angelfish, butterflyfish, and
hogfish were observed moving between the units and the natural reef. The
relatively close proximity, 50 m, of units to well-developed natural
reefs confused the question of attraction or production. Regular
observations of these species, and others, browsing on plants, sponges,
and invertebrates on the units made it apparent that additional food
sources and the structural diversity necessary for protection from
predators have been made available to both settlers and colonizers.
Although this data has limited usefulness in determining fish production
at the artificial reefs during the two-year period, the derived lists of
settlers and colonizers point out species and species groups with
potential to be produced by these types of habitats, as well as those
species that increase their biomass by consuming reef resources and
benefit by the new shelter provided.

The degree of fishery production at an artificial reef appears to be a
function of location (isolation reduces attraction), structural
complexity, and requirements and sizes of individual species at
different life stages. Bohnsack (1989) predicts that production should
be more important for reef dependent, habitat limited species at
artificial reefs in isolated locations. In this study only the rubble
reefs could be considered isolated. Impacts to natural reefs in the Keys
through the attraction of fish to relatively small artificial reefs is
considered minimal in light of an annual harvest of about 4,000,000
pounds of reef fishes in the Keys (F. Little, pers. comm., 1992) and
many thousands of aquarium fishes.

Typically, settlers were smaller species valued as primary marine life
fishes, and colonizer species were larger with importance to commercial
and recreational fisheries. Generally, settler species outnumbered
colonizers (Figs. 16 and 17), but only at the shallow units did settler
biomass exceed colonizer biomass excluding three large nurse sharks).
Both the mid-depth and deep units averaged about 10 kg of colonizer
species biomass in each sample, representing most of the biomass at
these sites. Overall at the units, settler species represented about 66%
of individuals but only 9% of total biomass.

The proportions of settler species to total species at mid-depth and
deep units, with few exceptions, showed comparable seasonal trends (Fig.
18). The percentage of settler species was highest (60% to 80%) the
first few months, lowest the first winter (March), and about 50% to 60%
thereafter at both sites. The relative abundance of settlers was high
(60% to 90%) the first few months, low (40% to 50%) the first winter,
and elevated again the second summer (Fig. 19). General decreases in the
numbers of species and individuals on artificial reefs in the winter in
south Florida are also reported by Bohnsack and Talbot (1980) and
Bohnsack *et al.* (1989).

4.1.1. Shallow Prefabricated Units .1.1. Shallow Prefabricated Units ;

Settler species accounted for 90% of individuals at the shallow units,
but only one-half (34/67) of species (Table 26), Gray angelfish (44 kg)
represented 85% of settler biomass, while bluehead wrasse and slippery
dick were the most abundant and most frequent settlers. Of the 34
settler species, one was primary commercial, three secondary commercial,
three recreational, 17 primary marine life, ten secondary marine life,
and three had no value designation.

Most abundant and frequent colonizers were doctorfish, hogfish, and
spotfin butterflyfish (Table 26). Three large nurse sharks represented
80% of total biomass for the shallow units. Colonizers included four
primary commercial species, four secondary commercial, seven
recreational, seven primary marine life, and eleven secondary marine
life. Seven colonizers had no fishery value designation.

4.1.2. Mid-Depth Prefabricated Units .1.2. Mid-Depth Prefabricated Units
;

About 65% of individuals and 31 of 73 species recorded at the mid-depth
units were considered settlers, but settlers comprised only 9% of total
biomass (Table 27). The most abundant settlers were bluehead wrasse,
tomtate, striped grunt, and bridled goby; the most frequent were blue
tang, bluehead wrasse, sharpnose puffer, and porkfish. All but one
settler species had a value designation; three were primary commercial
species, five secondary commercial, four recreational, 17 primary marine
life, and six secondary marine life.

Yellowtail snapper, mackerel scad, and ocean surgeon were the most
abundant colonizers. Ocean surgeon, slippery dick, doctorfish, hogfish,
and gray angelfish were the most frequent. Yellowtail snapper
represented 28% of total biomass for the two units and reached a high of
98 individuals in a single unit count (MAR1 in November 1989). Large but
infrequent visitors were greater amberjack and barracuda. Seven primary
commercial species, two secondary commercial, nine recreational, seven
primary marine life, and 19 secondary marine life were colonizers. Seven
colonizers had no designated economic value.

4.1.3. Deep Prefabricated Units .1.3. Deep Prefabricated Units ;

About 42% of the fishes and half of the species (34/69) at the deep
units were settler species, but settlers made up only 0.4% of the total
biomass of 389 kg (Table 28). The most abundant settlers were bluehead
wrasse, bridled goby, and bicolor damselfish; the most frequent were
graysby, bluehead wrasse, sharpnose puffer, and yellowhead wrasse.
Settlers included three primary commercial species, three secondary
commercial, four recreational, 21 primary marine life, and 10 secondary
marine life. All settler species had a designated economic value.

The most abundant colonizers were yellowtail snapper, gray snapper,
slippery dick, doctorfish, and 1,000 round scad on one occasion; the
most frequent were hogfish, slippery dick, yellowtail snapper, gray
snapper, and spotfin butterflyfish. Yellowtail and gray snapper
represented 14% and 18%, respectively, of the total biomass on the two
units. Maximums of 26 gray snapper (March 1990) and 49 yellowtail (June
1990) were recorded in a single unit count. Large but infrequent
visitors were greater amberjack, mutton snapper, barracuda, permit, and
cubera snapper. Colonizers included eight primary commercial species,
two secondary commercial, 13 recreational, five primary marine life, and
ten secondary marine life. Six colonizer species had no value
designation.

4.1.4. Bahia Honda Rubble Reefs .1.4. Bahia Honda Rubble Reefs ;

Settler species made up 93% of fishes counted on patch reefs at Bahia
Honda, a result of recording 19,955 tomtate, and represented nearly half
(43/90) of all species (Table 29). Excluding tomtate, settler species
accounted for three-quarters of the remainder. Reef croaker,
unidentified juvenile grunts, cocoa damselfish, bridled goby, and gray
snapper were other abundant settlers; the most frequent were tomtate,
cocoa damselfish, porkfish, blue tang, and striped parrotfish. Settlers
represented one-third of total biomass (915 kg) with tomtate, black
grouper, and gray snapper making up three-quarters. Settler species
included six primary commercial species, three secondary commercial,
seven recreational, 21 primary marine life, and 12 secondary marine
life. Only two species had no designated value.

Sixty-nine percent of colonizers were in infrequent schools of clupeids
and scad. Other abundant colonizers included bluestriped grunt, white
grunt, and snook (Table 29). The most frequent colonizers were white
grunt, bluestriped grunt, butter hamlet, snook, and rainbow parrotfish.
Seventy-eight percent of colonizer biomass was in 76 snook estimated to
weigh 453 kg (1,000 lbs.). Colonizers included eight primary commercial
species, nine secondary commercial, 16 recreational, five primary marine
life, and 14 secondary marine life. Nine colonizer species had no
economic value.

4.1.5. American Shoal Rubble Reefs .1.5. American Shoal Rubble Reefs ;

Settler species represented 71% of the individuals and 42% of the
species (30/72) at the American Shoal rubble reefs (Table 30). Tomtate
(10,207) accounted for 89% of settlers; excluding tomtate showed
settlers comprising 26%. Other abundant settlers were lane snapper,
striped parrotfish, and porkfish. The most frequent were striped
parrotfish, tomtate, redband parrotfish, cocoa damselfish, lane snapper,
porkfish, and slippery dick. As a result of 736 kg of tomtate, settler
species represented 51% of total biomass (1,430 kg), and lane snapper,
gray angelfish, and porkfish also contributed. Settlers included three
primary commercial species, three secondary commercial, four
recreational, 17 primary marine life, and ten secondary marine life. All
settlers had an economic value.

White grunt accounted for 69% of colonizers with bluestriped grunt,
bigeye, gray snapper, and yellowfin mojarra also common. The most
frequent colonizers were white grunt, bluestriped grunt, spotfin
butterflyfish, spotted goatfish, ocean surgeon, and yellowfin mojarra.
White grunt accounted for 57% of total colonizer biomass (630 kg) with
bluestriped grunt, snook, bigeye, permit, and barracuda also important.
Colonizers included four primary commercial species, seven secondary
commercial, ten recreational, five primary marine life, and 14 secondary
marine life. Nine species had no attributed economic value.

4.2. Objective 2. Compare the community structure of reef fishes on
prefabricated habitats to nearby natural reefs. .2. Objective 2. Compare
the community structure of reef fishes on prefabricated habitats to
nearby natural reefs. ;

The effectiveness of efforts to create artificial habitats to mimic and
supplement natural reefs may best be measured by comparing the fish
communities that develop with those on natural reefs in similar depths.
The length of time required for artificial habitats to become relatively
stable in terms of fish community structure appears to be primarily
functions of location, reef type and size, and the rate of fouling
community development. At the end of two years of monitoring, numbers of
species and individuals at the shallow (Figs. 10 and 11) and mid-depth
units (Figs. 12 and 13), although variable, seemed to have stabilized
while at the deep units there was a gradual increasing trend in
abundance (Figs. 14 and 15).

Data for artificial and natural reefs are often not precisely comparable
due to different census methods used and because the stationary census
method may underestimate fish abundance (Bohnsack and Bannerot, 1986;
Bohnsack *et al.,* 1989). As well, density estimates for the units based
on total counts may overestimate true density because the area of sand
surrounding the units is not included in density calculations. Most
fishes censused at the units, however, are structure oriented species
present as a direct result of the unit placement. The large number of
year-round stationary censuses over sizeable areas of the natural reefs
should insure relatively accurate estimates of fish abundance for these
habitats. Even with the different methods used, relative abundance
estimates should be comparable (Bohnsack *et al.,* 1989). Bohnsack *et
al.* (1991) report that most comparative studies of artificial and
natural reef fish communities show considerable similarity in species
composition although abundance and biomass may vary.

A comparison of the number of species (Fig. 7) and density (Fig. 8) for
all sites studied reflects greater species richness on natural reefs but
higher density on artificial habitats. On average, the units showed only
about 62% as many species as the adjacent natural reefs. About half of
the species at the natural reefs were also recorded at the nearby units
(Table 11).

4.2.1. Similarity of Units to Natural Reefs .2.1. Similarity of Units to
Natural Reefs ;

Comparison of species lists for each depth revealed similar percentages
of unit species shared with the nearby natural reefs, ranging from 75%
to 78% (Table 11). Small cryptic species often appeared in total counts
of the units but were usually missed in stationary censuses on adjacent
natural reefs. For example, twospot cardinalfish and seaweed blenny were
important constituents of fish populations at the shallow units but were
not recorded at the adjacent natural reef, although they undoubtedly
occur there. Other than infrequent schooling scad, every species with
more than eight individuals recorded at the mid-depth units was also
found at the adjacent natural reef. At the deep units, other than
twospot cardinalfish, every species with more than seven individuals was
also recorded at the deep natural reef.

The number of species on each set of units was only 55% to 56% of the
total species at each depth (Table 11). The percentages of the pool the
units shared with nearby natural reefs, 42% to 44%, were also low and
very similar.

Sixty-seven species were recorded at the shallow units and 104 at the
shallow natural reef. In decreasing order, wrasses, grunts,
surgeonfishes, combtooth blennies, and cardinalfishes were the most
abundant families at the units and damselfishes, wrasses, grunts,
surgeonfishes, and parrotfishes the most abundant at the natural reef.
Density of fishes was 1.6 inds./m2 at the shallow units and 0.9/m2 at
the adjacent natural reef.

Seventy-six species occurred at the mid-depth units and 114 species at
the mid-depth natural reef. Grunts, wrasses, jacks, snappers, and
surgeonfishes were most abundant at the units and grunts, damselfishes,
wrasses, jacks, and parrotfishes the most abundant at the natural reef.
Fish density at the mid-depth units was 4.2 inds./m2; at the adjacent
natural reef density was 1.2/m2.

Sixty-nine species were found at the deep units and 109 species at the
deep natural reef. Wrasses, snappers, gobies, damselfishes, and jacks
were the most abundant groups on the units, and grunts, damselfishes,
jacks, snappers, and gobies the most abundant on the natural reef. In
terms of biomass, snappers, jacks, surgeonfishes, barracuda, and
angelfishes were the most abundant on the most important at the units
and grunts, jacks, snappers, angelfishes, and sea basses most important
at the natural reef. Mean fish was 2.6 times greater on the deep units
(126 g) compared to the adjacent natural reef (48 g).

4.2.2. Similarity of Rubble Reefs to Other Reefs .2.2. Similarity of
Rubble Reefs to Other Reefs ;

Combined Hawk Channel rubble reefs produced a species total (103) close
to that of all prefabricated units (108) and fish density (4.9/m2)
slightly higher than the mid-depth units, nearly double that of the deep
units, and three times that of the low shallow units (Figs. 7 and 8).
Even with sizeable areas of sand included in many censuses, fish density
was three to five times higher at rubble reefs than at the natural
reefs. Mean fish size at Hawk Channel reefs (55 g) was smaller than that
at the mid-depth (76 g) and deep units (126 g) and close to that of the
deep natural reef (48 g).

The greater number of species and higher density at Bahia Honda (90
species, 5.9 inds./m2) than at American Shoal (72 species, 3.8/m2) may
result from its location, directly offshore from and within the
influence of Bahia Honda Channel, a deep, active channel that connects
the Gulf of Mexico to the Atlantic. The Bahia Honda site is also in
close proximity (50 m) to seagrass beds that extend offshore to the 9 m
contour along the north edge of Hawk Channel. The American Shoal reefs
are the most isolated from seagrass or hardbottom habitats of all sites
studied. The most abundant families at Bahia Honda reefs were, in
decreasing order, grunts, drums, herrings, jacks, and damselfishes, and
at the American Shoal site the most abundant were grunts, snappers,
parrotfishes, damselfishes, and wrasses. Based on biomass, the most
important families at Bahia Honda were snook, grunts, sea basses,
parrotfishes, and snappers, and at American Shoal the most important
were grunts, snook, snappers, bigeyes, and jacks. Mean fish size was
nearly 3 times larger at American Shoal (90 g) than at Bahia Honda (33
g), mainly as a result of larger tomtates at American Shoal.

Comparison of the Hawk Channel sites (9 to 12 m depth) to the mid-depth
natural reef (10 to 12 m depth) showed that 75% of artificial reef
species were shared with the natural reef, a percentage similar to the
relationship between units and natural reefs (Table 11). However, a
somewhat higher proportion (55%) of the species pool was shared and a
higher percentage (74%) of the pool was found at the rubble sites. About
half of the bridge rubble at the Hawk Channel reefs was placed in 1983
and 1985, the remainder in 1987.

4.2.3. Comparison of Top 15 Species .2.3. Comparison of Top 15 Species ;

To measure similarity between sites, comparisons were made of the 15
most frequently occurring and abundant, and in some cases, heaviest
species. The number of top 15 species in common to two sites was divided
by the total number of top 15 species at the two sites to obtain an
index of similarity. Various comparisons between artificial and natural
reefs are at Table 16.

Assessment of the similarity of dominant species on artificial and
natural habitats indicates substantial variation in fish populations
between units and natural reefs but high similarity among prefabricated
units of the same depth. Comparison of sets of prefabricated units to
the adjacent natural reefs showed highest similarity (33%) of the 15
most frequent species at the shallow reefs (Table 31) and lowest (22%)
at the deep reef (Table 33). Of the 15 most abundant fishes, similarity
was greatest (30%) at the mid-depth reefs (Table 32) and lowest (15%) on
the deep reefs. Biomass was compared only between the 15 heaviest
species on the deep reefs. Thirty percent similarity occurred with scad
and snapper, the heaviest fishes on the deep units, and scad and grunts,
the heaviest on the deep natural reef.

Although low similarity was recorded between dominant species at the
units and natural reefs, the nearly identical high units placed in deep
water showed the highest similarity of all reef comparisons with 88% of
the 15 most frequent species and 76% of the 15 most abundant species
common to both units (Table 21a). The two high units placed at the
mid-depth site showed 72% similarity of the 15 most frequent species and
67% similarity of the 15 most abundant species (Table 17). Although
comparisons were not made for the low shallow units, review of data
indicates relatively high similarity, with bluehead wrasse, slippery
dick, seaweed blenny, sharpnose puffer, porkfish, small grunts, and 3
species of surgeonfish as common elements.

4.2.4. Length-Frequency Comparisons .2.4. Length-Frequency Comparisons ;

Based on mean lengths it appears that artificial habitats studied here
may have provided shelter and protective cover useful to small
individuals of some species. Comparisons between the units and nearby
natural reefs showed many species with similar mean length, but a few
common species with apparent differences. Assessment of length data must
take into account the probability that the total count method used on
units is biased towards recording more small fish than the stationary
sampling method used on natural reefs.

At mid-depth reefs (Tables 15 and 18), common species with shorter mean
length at units included bicolor damselfish (32% smaller), bluehead
wrasse (-32%), yellowhead wrasse (‑34%), graysby (-38%), and cottonwick
(-46%). Doctorfish and ocean surgeon were both 26% larger on the units
than at the mid-depth natural reef. At the deep reefs (Tables 21 and
22), smaller species on the deep units included bicolor damselfish (25%
smaller), bluehead wrasse (-28%) reef butterflyfish (-31%), graysby
(-48%), spotfin hogfish (-57%), yellowhead wrasse (-59%), and blackfin
snapper (-68%). Doctorfish and ocean surgeon were 34% larger on the deep
units than on the deep natural reef.

Mean length data from the Hawk Channel sites (Table 25) were compared
with the mid-depth natural reef. Hawk Channel data were all collected in
the summer, possibly resulting in more juveniles recorded, while natural
reef censuses were made over two years. Common fishes with substantially
smaller mean length at the rubble habitats than at MNR were queen
angelfish (36% smaller), sharpnose puffer (-38%), porkfish (-38%), and
blue angelfish (-43%). Fishes larger on rubble reefs were spotted
goatfish (29% larger) and tomtate (+57%). *Acanthurus* surgeonfishes
(251 inds.) averaged 14.6 cm long on the Hawk Channel rubble reefs and
15.0 cm on the mid-depth natural reef (398 inds.).

4.3. Objective Number 3. Evaluate the effects of reef siting at
different water depths on species composition, recruitment and biomass.
.3. Objective Number 3. Evaluate the effects of reef siting at different
water depths on species composition, recruitment and biomass. ;

Water depth appears to be an important factor affecting fish assemblages
that develop on artificial habitats, although little information is
available on the placement of similar structures or materials at
different depths. Here, due to structural differences between the low
profile shallow units and the high profile mid-depth and deep units,
direct comparisons are made only between the latter two depths. Data
from the shallow units provide information on species that could be
expected on artificial habitats in this depth on the reef tract.

4.3.1. Species Composition, Frequency, and Abundance .3.1. Species
Composition, Frequency, and Abundance ;

There were some notable differences in fish assemblages on the mid-depth
and deep units. For example, seven species of grunts totaled 1,335
individuals on the mid-depth units, but only two grunts of two species
were recorded on the deep units. The greater abundance of large
predators on the deep units probably limited utilization by juvenile and
sub adult grunts, and less undermining by wave surge with increased
depth resulted in fewer microhabitats. Surgeonfishes, especially ocean
surgeon and blue tang, were considerably more abundant on the mid units
(13.6/count) than on the deep units (3.0/count), where less food
appeared available for these herbivores. Sergeant majors, water column
feeders, were numerous at the mid-depth units, but virtually none were
recorded in deep water. Bluehead wrasse were 75% more abundant at
mid-depth, and *Chromis*, blackfin snapper, bicolor damselfish, and
*Bodianus* hogfish were more abundant at the deep units. A single gray
snapper and 337 yellowtail snapper (26 cm ave. length) were recorded on
the mid-depth units and 154 gray snapper (31 cm) and 231 yellowtail
snapper (25 cm) on the deep units. Thirty-seven hogfish were recorded
from both sets of units, just over one per sample.

Species among the 15 most frequent on the mid-depth units but not on the
deep units were blue tang, ocean surgeon, porkfish, gray angelfish,
sergeant major, and cottonwick (Tables 32 and 33). Frequent only at the
deep units were yellowtail snapper, yellowhead wrasse, gray snapper,
bicolor damselfish, and greater amberjack. Frequent species common to
both sets of high units were bluehead wrasse, graysby, hogfish, slippery
dick, sharpnose puffer, spotfin butterflyfish, doctorfish, bridled goby,
twospot cardinalfish, and reef butterflyfish.

Ranked in the 15 most abundant species at the mid-depth, but not at the
deep units, were blue tang, cottonwick, and ocean surgeon; in the top 15
only at the deep units were bicolor damselfish, gray snapper,
doctorfish, sharpnose puffer, graysby, greater amberjack, and hogfish
(Table 32 and 33). Shared of the 15 most abundant species were bluehead
wrasse, bridled goby, yellowtail snapper, twospot cardinalfish, slippery
dick, and yellowhead wrasse.

Frequently occurring species common to the units in all depths were
slippery dick, bluehead wrasse, sharpnose puffer, doctorfish, twospot
cardinalfish, and hogfish (Tables 31, 32, and 33). Only bluehead wrasse,
slippery dick, and twospot cardinalfish were included in lists of the
top 15 most abundant species at all units.

Although all three sets of units had similar numbers of species,
dominant species and their relative abundance differed with depth.
Comparisons of the 15 most frequent and abundant species at the
mid-depth and deep units showed only 48% similarity of frequent species
and 25% similarity of abundant species (Table 16). The shallow units
shared with the mid-depth units 50% of the 15 most frequent species and
36% of the most abundant. Shared between the shallow and deep units were
32% of the frequent species and 30% of the most abundant.

A number of species were relatively common at most depths, and several
had higher mean abundance in Hawk Channel then at the units on the reef
tract. Thirty six species occurred as one of the 15 most frequent at one
or more artificial reefs (Table 36). Only doctorfish and slippery dick
were listed for all five artificial reef sites; frequent species at
three or more were hogfish, porkfish, sharpnose puffer, bicolor
damselfish, blue tang, bluehead wrasse, gray angelfish, ocean surgeon,
spotfin butterflyfish, and twospot cardinalfish. Frequent only at the
two Hawk Channel sites were tomtate (top ranked at both), cocoa
damselfish, striped parrotfish, and white grunt. Listed only at one Hawk
Channel site were black grouper, blue angelfish, bluestriped grunt, lane
snapper, queen angelfish, redband parrotfish, reef croaker, and spotted
goatfish. Frequent only at the units were bluehead wrasse, twospot
cardinalfish, graysby, reef butterflyfish, bridled goby, cottonwick,
greater amberjack, puddingwife, sergeant major, seaweed blenny,
yellowhead wrasse, and yellowtail snapper.

Thirty-eight species were ranked as one of the 15 most abundant at one
or more artificial reefs (Table 37). In the top 15 at all artificial
reefs was slippery dick; at three or more were bluehead wrasse, bridled
goby, tomtate, bicolor damselfish, gray snapper, lane snapper, porkfish,
twospot cardinalfish, and an unidentified grunt. In the 15 most abundant
only in Hawk Channel were bluestriped grunt, cocoa damselfish, striped
parrotfish, white grunt, bigeye, redband parrotfish, reef croaker,
clupeids, and yellowfin mojarra. Eighteen species abundant only at
prefabricated units included twospot cardinalfish, blue tang,
doctorfish, ocean surgeon, sharpnose puffer, striped grunt, yellowhead
wrasse, and yellowtail snapper.

4.3.2. Recruitment and Colonization .3.2. Recruitment and Colonization ;

The mean number of species per census at a unit ranged from a low of ten
at two of the shallow units to a high of 17 at MAR2, with deep units
intermediate (Fig. 9). After excluding a single school of 1,000 round
scad recorded at a deep unit and 800 juvenile grunts from a mid-depth
sample, the average number of fish per census was lowest at SAR (46 - 49
fish) and highest at MAR (100 - 127), with DAR units (69 - 71)
intermediate (Fig. 9). Mean species per month at the units showed
comparable seasonal variation with highest numbers during warmer months
(Fig. 20). Following peaks during the initial four months, total fishes
declined somewhat, and then increased the second year at all units (Fig.
21).

The simple structure of the low units apparently resulted in low
diversity and abundance compared to the larger units, even though census
data from the shallow natural reef shows high species richness in the
area. Fifteen species totaled more than 100 individuals at the mid-depth
units (N = 32), seven species totaled more than 100 individuals at deep
units (N = 30), but only two species (bonehead wrasse and slippery dick)
showed more than 100 individuals at the shallow units (N = 42).

Settler species recruited to the units were generally the small species
most valued by the marine life industry (Tables 26, 27, and 28). The
number of settler individuals per census ranged from 43 (SAR) to 65
(MAR), with DAR intermediate with 44 (Fig. 16)

4.3.3. Biomass .3.3. Biomass ;

The relatively low similarity of frequent and abundant species at
different depths appeared also true in terms of the heaviest species at
different depths. Although mean biomass was similar, 10.5 kg/sample and
13.0 kg/sample, at the mid-depth and deep units respectively, they
shared only 43% of the 15 heaviest species (Tables 32 and 33). The
shallow units (Table 31) shared 25% of the 48 heaviest species with the
mid-depth units and 30% of the heaviest species with the deep units.
Except at the shallow units, settler biomass represented a small portion
of overall biomass (Fig. 16).

Comparison of the 15 heaviest species showed mid-depth and deep units
sharing yellowtail snapper, ocean surgeon, greater amberjack, barracuda,
gray angelfish, doctorfish, bar jack, hogfish, and French angelfish
(Tables 32 and 33). Several scad species, blue tang, porkfish, and blue
angelfish were additional important contributors of biomass at the
mid-depth units, while snapper (gray, mutton, and cubera), round scad,
permit, and yellow jack were additional important contributors at deep
units.

Heaviest species common to the units in all depths were gray angelfish,
hogfish, doctorfish, ocean surgeon, and French angelfish. Three large
nurse sharks comprised 69% of the total biomass (253.91 kg) at the
shallow units and gray angelfish 56% of the remainder. Yellowtail
snapper made up 28% of total biomass (334.86 kg) at the mid-depth units,
surgeonfish 18%, scad 14%, and other jacks 12%. One large school of
round scad made up 23% of total biomass (389.37 kg) at the deep units,
snappers (gray, yellowtail, cubera, mutton) 44%, other jacks 11%, and
barracuda 6%.

Thirty-nine species were recorded as one of the 15 heaviest at one or
more artificial reefs (Table 38). Gray angelfish and hogfish were ranked
among the 15 heaviest at all five artificial reefs, and barracuda,
doctorfish, porkfish, French angelfish, gray snapper, ocean surgeon, and
yellowtail snapper were listed for three or more sites. Among species
with greatest biomass only at Hawk Channel sites were bluestriped grunt,
lane snapper, snook, tomtate, white grunt, bigeye, black grouper,
rainbow parrotfish, reef croaker, yellow goatfish, and yellowfin
mojarra. Listed only from the units were French angelfish, ocean
surgeon, bar jack, blue angelfish, greater amberjack, yellow jack, blue
tang, cero mackerel, cubera snapper, mackerel scad, margate, mutton
snapper, nurse shark, round scad, saucereye porgy, slippery dick, and
spotfin butterflyfish.

4.4. Objective number 4. Separate fish communities into trophic levels
to assess location of food source (i.e. water column, surrounding
bottom, structure fouling community, etc.). .4. Objective number 4.
Separate fish communities into trophic levels to assess location of food
source (i.e. water column, surrounding bottom, structure fouling
community, etc.). ;

Because many fish species are food generalists that consume a wide
variety of items, separating species by trophic levels is often
imprecise and somewhat arbitrary (Bohnsack *et al.* 1987). The value of
the effort, however, is insight into food resource partitioning and
general ecology of the fish fauna, especially where species abundance
and biomass estimates are available.

Data from the mid-depth (Table 39) and deep units (Table 40), the deep
natural reef (Table 41), and the Bahia Honda rubble reefs (Table 42)
were assessed to determine the relative contributions to fish
assemblages of five primary types of feeders: browsers (consume sessile
invertebrates such as sponges, tunicates and polychaete worms attached
to hard surfaces), piscivores (consume fishes on and near reefs),
herbivores (consume plants from hard surfaces and surrounding bottom),
invertivores (consume various size invertebrates from hard surfaces and
surrounding bottom), and planktivores (consume plankton in water
column).

Of the sites assessed, piscivores dominated biomass, except at the deep
natural reef where invertivores dominated (Fig. 22). The proportion of
browser and herbivore biomass was highest at the mid-depth units and
lowest at the deep natural reef.

Planktivores dominated numbers except at Bahia Honda where invertivores
were by far the most abundant (Fig. 23), The proportion of piscivore
numbers was highest at the mid-depth units and comparable at the deep
reefs. Browser and herbivore numbers were lowest at the deep natural
reef and at Bahia Honda. Relative contributions of the 5 groups were
similar at the mid-depth and deep units, the main exceptions being
reduced biomass of herbivores and increased numbers of piscivores at the
deep units.

4.4.1. Browsers .4.1. Browsers ;

These omnivores obtain food directly from the hard surfaces of
artificial and natural reefs, with supply on artificial habitats mostly
functions of reef age, location, and substrate. The succession of the
fouling community on artificial surfaces affects the relative abundance
of fishes that depend on its various components.

The proportion of browser biomass was highest at the mid-depth (10%) and
deep units (6%), and mainly due to gray angelfish, along with French,
blue, and queen angelfish. Adult angelfish were often observed in pairs
browsing on the fouling community of these units (Plate 11). The
greatest proportions of browsers by abundance were also at the mid-depth
(3%) and deep (3%) units. Sharpnose puffer was a frequent browser,
especially at reef tract sites, while rock beauty was the most abundant
browser at the deep natural reef, and adult angelfish the most abundant
at Bahia Honda. Most browsers are important to the marine life industry.

4.4.2. Piscivores .4.2. Piscivores ;

Fish-eating predators use artificial reefs to capitalize on higher
density of prey or as shelter for protection and orientation. They
dominated total biomass at all sites except for the deep natural reef,
where invertivores dominated as a result of numerous grunts (Fig. 22).
Most piscivores are valued by commercial and recreational fisheries.
They made up 46% of biomass at the mid-depth units, with yellowtail
snapper (337 inds.), greater amberjack (22), barracuda (4), and cero (8)
most important. At the deep units, 53% of total biomass was contributed
by fish-eating species; the heaviest were gray snapper (154 inds.),
yellowtail snapper (231), cubera snapper (1), barracuda (4), and 45
greater amberjack (Table 40). Piscivores represented only about 20% of
total .biomass at the deep natural reef; most important were gray
snapper (76 inds.), greater amberjack (14), yellow jack (58), and
yellowtail snapper (18). The extensive use of wire fish traps in the
deep reef area may have resulted in reduced numbers of predators with
fishery value in censuses. Piscivores comprised the greatest proportion
(63%) of biomass at the Bahia Honda reefs, with 76 snook, along with
*Mycteroperca* groupers (114 inds.), gray snapper (164), and 5 barracuda
(Table 42).

The proportion of piscivores ranged from a low of 1% at Bahia Honda
where large numbers of grunts dominated, to a high of 15% at the deep
units where yellowtail and gray snapper were common, but grunts were few
(Fig. 23). At the mid-depth units the most common piscivore was
yellowtail snapper, but only a single gray snapper was recorded. On the
deep natural reef the most abundant piscivores were yellowtail snapper,
gray snapper, and yellow jack. At Bahia Honda they were gray snapper,
*Mycteroperca* groupers, and snook.

4.4.3. Herbivores .4.3. Herbivores ;

These species feed mostly on plants attached to or embedded in hard
surfaces and to a lesser degree on benthic plants on surrounding
bottoms. They contributed most to total biomass at the mid-depth units
(18%) and Bahia Honda rubble reefs (8%) and least at the deep natural
reef (3%) (Fig. 22). *Acanthurus* surgeonfishes represented 99% of
herbivore biomass at the mid-depth units, where only five parrotfishes
of three species were recorded, and 94% of herbivore biomass at the deep
units, where only two parrotfishes were recorded. Surgeonfishes and
parrotfishes dominated herbivore biomass at the deep natural reef, but
mean abundance of these groups was 74% and 21% lower than on the
mid-depth natural reef. On the Bahia Honda reefs, parrotfishes of nine
species (principally rainbow) accounted for 82% of herbivore biomass,
and surgeonfishes contributed 17%.

Ten herbivore species were recorded at both the mid-depth and deep units
but herbivore biomass was nearly three times higher at mid-depth, and
the number of herbivores more than 80% higher (Tables 39 and 40).
Surgeonfishes, often observed feeding on algae on the units, totaled 436
individuals at the mid-depth units but only 89 at the deep units. Only
doctorfish occurred at both depths in comparable numbers. Alevizon
(1990) notes that as a result of reduced light penetration, primary
production by plants is reduced on deep reefs as is the abundance of
herbivorous species.

4.4.4. Invertivores .4.4. Invertivores ;

Some of these species consume invertebrates that attach to or use
irregular hard surfaces as protective cover, others feed on surrounding
bottoms, usually at night, using reefs as protective cover when not
feeding. The greatest contribution by invertivores to total biomass
(Fig. 22) was on the deep natural (55%) and Bahia Honda reefs (26%), and
the least was on the mid-depth units (7%). At the mid-depth units, 25
species of invertivores were recorded with hogfish, porkfish, spotfin
butterflyfish, and a single mutton snapper making up 81% of invertivore
biomass. Five species of *Haemulon* grunts (1,299 inds., 3.65 kg) at the
mid-depth units were juvenile forms listed as planktivores instead of
invertivores based on observations of their feeding in schools on
plankton near the top of the units. At the deep units, 25 species of
invertivores were recorded but only a single porkfish and a single
*Haemulon* grunt. Mutton snapper (5 inds.), hogfish (37), permit (3),
and spotfin butterflyfish (35) made up 93% of invertivore biomass at the
deep units. Forty-five invertivores were recorded at the deep natural
reef with tomtate, white grunt, lane snapper, and bluestriped grunt
making up 81% of biomass. Thirty-nine were recorded at Bahia Honda with
tomtate, bluestriped grunt, white grunt, and porkfish making up 85% of
biomass. Although trophic information was not reviewed at American
Shoal, grunts (invertivores) alone accounted for 82% of total biomass
(22% at Bahia Honda).

The mid-depth units showed 10% invertivores with the most abundant being
yellowhead wrasse, slippery dick, reef butterflyfish, hogfish, graysby,
and spotfin butterflyfish (Table 39, Fig. 23). Thirteen percent of deep
unit species were invertivores; the most abundant were slippery dick,
yellowhead wrasse, graysby, hogfish, blackfin snapper, and spotfin
butterflyfish. Thirty-seven hogfish were recorded at both the mid-depth
and deep units, and were often observed removing bivalve mollusks and
other invertebrates from the structure\'s surface. The deep natural reef
showed 37% invertivores; the most abundant were tomtate, white grunt,
lane snapper, blackfin snapper, French grunt and yellowhead wrasse. The
greatest proportion of invertivores (90%) occurred at the Bahia Honda
site as a result of 19,955 tomtate (Fig. 23); removing tomtate showed
62% of the remaining number were invertivores with reef croaker, an
unidentified grunt, bluestriped grunt, white grunt, slippery dick, and
porkfish most abundant. Categorizing small juvenile tomtate at Bahia
Honda as planktivores (as at the mid-depth units) would increase the
proportion of planktivores, decrease the high proportion of
invertivores, but have little effect on the overall biomass (Figs. 22
and 23).

The foureye butterflyfish, a popular marine life species, is an example
of a common reef invertivore found to be rare on artificial habitats.
Five hundred twenty-six foureyes were recorded on natural reefs, but
only six at the Hawk Channel rubble reefs, and none at the units. One of
the most specific feeders of all common reef fish, feeding on small
polychaete worms and coelenterates, the foureye\'s absence from the
units was probably the result of food limitation or inadequate small
protective cover.

4.4.5. Planktivores .4.5. Planktivores ;

These fishes feed on planktonic plants and animals over the top of hard
surfaces that also serve as protective cover. They also occur in large,
fast moving schools that feed over extensive areas, regardless of bottom
type. It is likely that greater exposure to currents on high profile
reefs favors planktivores (Bohnsack *et al.,* 1989). The contribution of
planktivores to total biomass was similar at the mid-depth (19%) and
deep units (24%), and deep natural reef (18%), but was low at Bahia
Honda (1%), where 19,955 tomtates (ave. 9 cm length) were all considered
invertivores (Fig. 22). Scad and bar jack made up 92% of planktivore
biomass at the mid-depth units with minor contributions by juvenile
grunts and sergeant major. At the deep units, round scad and bar jack
made up over 99% of planktivore biomass; at the deep natural reef, round
scad made up 96% of planktivore biomass with contributions by bicolor
damselfish and bar jack. Making up most planktivore biomass at the Bahia
Honda site were two unidentified clupeids, an unidentified scad, and
dusky damselfish.

Sixty-one percent of the individuals at the mid-depth units were
planktivores (Fig. 23) with nine species each showing more than 100
individuals (Table 39); the most common were bluehead wrasse, juvenile
grunts (tomtates, striped, and cottonwick), and mackerel scad. Only
three *Chromis* of two species were recorded at the mid-depth units
while 783 *Chromis* of five species were recorded at the adjacent
mid-depth natural reef. Since the same food source should be available
at the mid-depth reefs, a greater concentration of predators, and the
lack of suitable small protective cover on the units, may have precluded
use by *Chromis*. Fifty-six percent of fishes at the deep units were
planktivores; 1,000 were round scad and most of the rest, bluehead
wrasse, bicolor damselfish and twospot cardinalfish. Only 38 *Chromis*
(3 species) were recorded at the deep units, but five species of
*Chromis* (2,191 inds.) made up 22% of planktivore numbers on the deep
natural reef. More than half of the individuals at the deep natural reef
were planktivores, dominated by round scad and juvenile grunts but with
large numbers of damselfishes. Planktivores represented only 5% of total
numbers at Bahia Honda with two clupeids and scad the most abundant, and
dusky damselfish the most frequent. Although suitable protective cover
appeared available at Hawk Channel reefs, no *Chromis* were recorded.

4.5. Objective Number 5. Document and quantify the plant and
invertebrate fouling community as a function of substrate and water
depth. .5. Objective Number 5. Document and quantify the plant and
invertebrate fouling community as a function of substrate and water
depth. ;

Artificial substrates placed in the marine environment of south Florida
attract reef biota, sessile organisms including corals, and other
natural reef growth (Jaap, 1984). The algae and wide variety of attached
invertebrates are a source of food for many fish, both residents of the
reef and visitors. About 66 m2 of new hard surface was provided by each
of the high units and several thousand square meters at each of the
rubble sites. Although long term expansion of the fouling community may
result in an increase in fishes dependent upon the food resources and
shelter provided, infilling of cracks, crevices, and holes by encrusting
organisms and sediment may act to reduce available shelter.

Fouling community photography at specific points (on concrete and PVC)
on the units was initiated about 2 and 1/2 months after placement and
was conducted on about a quarterly basis thereafter (Table 43).
Twenty-four images (about 0.57 m2 total area) were usually shot at each
depth.

Qualitative review of chronological sequences of photographs of
different substrates at different depths, along with field notes and
other photography (e.g. Plate 10), revealed useful information about
trends in succession of the fouling community. The color transparencies
are available for possible future quantitative analysis and comparison
to long term photography. Recorded as attached to the units were algae
(filamentous, encrusting calcareous, frondose, etc.), encrusting and
erect Porifera, Scleractinia, Octocorallia, encrusting and erect
Hydrozoa, encrusting and erect Bryozoa, Ascidiacea, Annelida worms, and
Mollusca (bivalves).

Within one year at MAR, unidentified hard corals measured 1 to 2 cm in
diameter and encrusting *Millepora* measured 10 cm diameter on high
concrete surfaces. By September, 1989, gorgonians on MAR were up to 8 cm
high and *Millepora* was spreading over much of the high PVC. By
January, 1990 hard corals at MAR measured 3 to 5 cm in diameter. In
October, 1989, several hard corals on SAR measured 2 to 4 cm diameter.

Inspection of the units in September, 1990 (27 months after placement)
showed greatest variety and extent of hard corals at MAR with SAR second
and a few hard corals at DAR. A substantial variety of small hard corals
up to 6 cm in diameter were recorded on MAR including *Porites
astreoides*, *Montastraea* *annularis*, *Manicina areolata*, *Meandrina*
sp., *Siderastrea* *radiata*, *Oculina diffusa*, and *Stephanocoenia*
sp. The hydrozoan *Millepora* was common at MAR with upright growth, and
octocorals were up to 20 cm tall. On SAR were the hard corals
*Mycetophyllia lamarckiana, Porites astreoides*, *Dichocoenia stokesii,
Siderastrea radiata, Siderastrea* *siderea* and *Colpophyllia natans.
Millepora* formed patches up to 22 cm diameter on SAR, and octocorals
were as tall as 20 cm.

Surfaces (concrete and PVC) elevated more than about 0.5 m above the
bottom fouled more rapidly and densely than surfaces close to the
bottom, (as an example compare lower images, Plates 10 and 11). Reduced
fouling near the bottom was probably the result of sand scouring from
storm-generated wave surge. For example, by early May, 1989 (about 10
months after placement), PVC on top of the mid-depth units (Fig. 6,
point 2) was considerably more fouled by encrusting and erect organisms
than PVC near lower edges (point 6). Feeding by benthic animals could
also affect fouling near the bottom.

Point 3, smooth concrete, located 2.5 m above the bottom of the high
profile units, fouled more rapidly and densely than point 5, also smooth
concrete, but only 0.3 m above the bottom (Fig 6). Close-up photography
showed fouling plants and animals gained a foothold on rough concrete
surfaces (point 4) on high units more rapidly than on smooth concrete
surfaces (point 3).

Within a year on MAR and DAR units, the small bivalve mollusk
*Dendrostrea frons* (frons oyster) and the spiny oyster (*Spondylus
americanus*) became common, both alive on units and as shell debris on
the bottom under the unit. Hogfish were observed feeding on mollusks
attached to the units, and with angelfish, surgeonfish, and
butterflyfish, were common consumers of fouling resources (Plates 11 and
12).

4.6. Objective Number 6. Determine if large, fabricated habitats can
provide significant fishing opportunities. .6. Objective Number 6.
Determine if large, fabricated habitats can provide significant fishing
opportunities. ;

Fishing is the major direct use of artificial reefs (Bohnsack *et al.,*
1989), although diving and non-consumptive uses are gaining in
popularity in the Florida Keys, especially on sunken vessels. In the
past, assessment of the economic value of artificial reefs has been
related to commercially or recreationally important species taken by
hook and line, and to the diving community (Milon, 1991). Here
assessment also includes species important to the marine life industry,
a substantial fishery in south Florida regulated by the state of Florida
(Chap. 46-42.001 FAC). Species were categorized as \"primary\" -
generally targeted by a fishery with directed effort or \"secondary\" -
of value to the fishery but generally not targeted.

Reef fish landings for the Florida Keys and their monetary value are
readily available only for commercial hook and line species. Preliminary
data shows nearly 4,000,000 pounds landed in 1990 worth about \$5.4
million at dockside (E. Little, pers. comm, 1992). Seven species of
snapper made up 54% of landings in 1990, amberjack 25%, and groupers
about 11%. Overall in this study, 54% of total fish biomass at
artificial reefs (3,323 kg) were commercially important species.

Rockland (1988) estimated that all recreational fishing in the Florida
Keys resulted in output of about \$63 million. Targeted recreational
species at artificial habitats in the Keys include most commercial
species as well as barracuda, permit, and snook. Recreational marine
life harvest for home aquariums is a substantial activity, as well.

Fish assemblages were assessed to determine which species had
commercial, recreational, or marine life value. Comparison of the
relative importance of species of different fisheries at each reef
habitat follows (numbers do not total 100% as some species have more
than one value, the number of species are in parentheses):

Units combined Hawk Channel Natural

VALUE (N = 104) (N = 5O) (N = 257)

Primary commercial 13.9% (15) 15.2% (16) 12.8% (20)

Secondary commercial 6.5% (7) 9.5% (10) 7.1% (11)

Recreational 18.5% (20) 21.9% (23) 17.3% (27)

Primary marine life 35.2% (38) 30.5% (32) 28.8% (45)

Secondary marine life 29.6% (32) 27.6% (29) 36.5% (57)

None established 13.9% (15) 12.4% (13) 12.2% (19)

Total species 108 103 153

Units were comparable to the natural reefs in relative proportion of
valued species in all categories, with the proportion of primary marine
life species slightly higher at the units. Hawk Channel rubble reefs
showed a higher percentage of commercially and recreationally important
species than other habitats. Species harvested by the marine life
industry accounted for 65% of total species recorded at both the units
(70 species) and the natural reefs (102 species), and 58% of those
recorded at the Hawk Channel reefs (62).

4.6.1. Shallow Prefabricated Units .6.1. Shallow Prefabricated Units ;

Only 22 individuals of five species of primary commercial importance
were recorded at the shallow units; 15 were hogfish averaging 26 cm
long. Three mutton snapper averaging 38 cm and an 80-cm black grouper
were also recorded. Seven species of grunts dominated the secondary
commercial category, but, with the exception of a single 40-cm margate
and 61 porkfish averaging 9 cm (to 28 cm), all were juveniles, only 9%
of biomass was due to species important to commercial fishing.

Ten recreational species included those important to the commercial
industry along with yellow jack. The most abundant fishes at SAR were
those important to the marine life fishery. Twenty-four primary marine
life species were recorded, the most abundant were bluehead wrasse (724
inds.), gray angelfish (46), sharpnose puffer (59), two-spot
cardinalfish (60), blue tang (42), bicolor damselfish (31), and spotfin
butterflyfish (12). Common secondary marine life species (21) were
slippery dick (389), doctorfish (79), ocean surgeon (68), seaweed blenny
(99), and 3 nurse sharks that averaged 58 kg in weight. Only ten species
and 2% of individuals at the shallow units had no economic value.

4.6.2. Mid-Depth Prefabricated Units .6.2. Mid-Depth Prefabricated Units
;

Ten species of primary commercial value were recorded at the mid-depth
units with yellowtail snapper (337 inds.), hogfish (37), greater
amberjack (22), and cero (8) the most important (Table 39). Only one
gray snapper and one mutton snapper were recorded. Beginning just over a
year after placement, numbers of yellowtail snapper (ave. 26 cm)
increased and ranged up to over 100 in a single combined count (Fig.
24). Yellowtail snapper were regularly seen schooling and appeared to
orient to the PVC stacks on these units (Plate 12). Seven species of
grunts (1,027 inds.) represented most of the secondary commercial
species, but all were juveniles except for a few margate and cottonwick,
and 34 porkfish averaging 18 cm. Commercial species represented 44% of
total biomass on these units.

Thirteen species of recreational importance included the primary
commercial species along with four barracuda averaging 6 kg, margate,
and porkfish.

Twenty-four species of primary interest to the marine life industry
included bluehead wrasse (659 inds.), blue tang (121), yellowhead wrasse
(111), twospot cardinalfish (109), sharpnose puffer (83), bicolor
damselfish (67), reef butterflyfish (37), gray angelfish (32), and
spotfin butterflyfish (32). Twenty-five secondary marine life species
included masked goby (273), ocean surgeon (223), slippery dick (108),
doctorfish (92), sergeant major (39), graysby (37), and porkfish.
Although blue chromis, brown chromis, purple reeffish, rock beauty, and
foureye butterflyfish were common marine life species on the adjacent
natural reef, only a single brown chromis was recorded on the units.
Eight species and 19% of individuals on the mid-depth units had no
economic value.

4.6.3. Deep prefabricated Units .6.3. Deep prefabricated Units ;

Twelve species of primary commercial importance were recorded at the
deep units with yellowtail snapper (231 inds.), gray snapper (154),
greater amberjack (45), hogfish (37), and mutton snapper (5) represented
by adults. A single large cubera snapper (27 kg) and one cobia were also
recorded. Seventy-seven gray snapper were recorded on both DAR1 (ave.
31.5 cm) and DAR2 (ave. 30.8 cm). The number of both yellowtail and gray
snapper appeared to increase in year 2 over year 1 with abundance peaks
for the two species occurring in different censuses (Fig. 25) . The same
number of hogfish (37) were recorded at the deep units (ave. 25.5 cm) as
at the mid-depth units (ave. 23.3 cm).

Only four individuals of three species of secondary commercial value
were recorded on the deep units. Although nearly 1,000 *Haemulon* grunts
(secondary commercial) were recorded at the mid-depth units and 7,200
grunts of eight species were recorded at the deep natural reef, only 2
juvenile grunts occurred on the deep units.

Seventeen recreational species included the primary commercial species
as well as 4 barracuda that averaged 6 kg, 3 permit, and 5 yellow jack.

Twenty-eight primary marine life species included bluehead wrasse (375
inds.), bicolor damselfish (157), twospot cardinalfish (117), yellowhead
wrasse (83), sharpnose puffer (60), spotfin butterflyfish (35),
yellowtail reeffish (23), and reef butterflyfish (20). Twenty secondary
marine life species included masked goby (298 inds.), slippery dick
(84), doctorfish (74), and graysby (54). Excluding one school of 1,000
round scad showed that only 1% of fishes (5 species) at the deep units
had no economic value.

4.6.4. Hawk Channel Bridge Rubble Reefs .6.4. Hawk Channel Bridge Rubble
Reefs ;

These sites are not \"prefabricated\" artificial habitats, but materials
were specifically placed to form patch reefs with control over type of
material, area covered, patch location, and vertical profile. The desire
was to create conditions suitable to enhance the fish population of a
chosen area, particularly for species valuable to commercial and
recreational fishermen. A project summary (Kruer, 1985) written prior to
placement of the first 11 patches at Bahia Honda predicted:

> \"Species of importance expected to utilize this habitat include
> black, gag and red grouper, mangrove, lane, mutton, yellowtail, and
> schoolmaster snapper, hogfish, cobia, barracuda, Spanish and cero
> mackerel, porgies, permit, snook, grunts, baitfish, tropicals, spiny
> lobster, stone crab and others\".

4.6.5. Bahia Honda Rubble Reefs .6.5. Bahia Honda Rubble Reefs ;

Fourteen primary commercial species were recorded at the Bahia Honda
site (N = 26) with gray snapper (164 inds.), lane snapper (89), gag
grouper (71), hogfish (46), and black grouper (30) occurring in half or
more samples (Table 42). One hundred fifteen *Mycteroperca* groupers
ranged from 5 to 100 cm in length (ave. 26 cm). Gray snapper averaged 25
cm long and ranged up to 40 cm. Other adult primary commercial species
were yellowtail (10), cero (6), Nassau grouper (3), red grouper (1), and
mutton snapper (1). Six species of *Epinephelus* groupers totaled 23
individuals.

Twelve secondary commercial species dominated the population as a result
of 20,739 grunts of seven species, including 19,955 tomtate that
averaged 9 cm long. Manooch and Barans (1982) report that tomtates are a
major food source for higher trophic level fishes in the
southeastern US.

The 23 recreational species included those of primary commercial value
as well as 76 snook that averaged 6 kg each, porkfish (130 inds.), adult
barracuda (5), and permit (1).

Twenty-six primary marine life species included cocoa damselfish (250),
blue tang (79), doctorfish (75), queen angelfish (35), sharpnose puffer
(35), gray angelfish (34), blue angelfish (31), and spotfin
butterflyfish (23). Important secondary marine life species (26) were
masked goby (174 inds.), striped parrotfish (156), slippery dick (139),
porkfish (130), and dusky damselfish (42). Because of 3,276 reef
croaker, along with large schools of scad and clupeids, 18% (11 species)
of the total individuals had no economic value.

4.6.6. American Shoal Rubble Reefs .6.6. American Shoal Rubble Reefs ;

Seven primary commercial species were recorded at the American Shoal
site (N = 24) including lane (249 inds.), gray (56), and yellowtail
snapper (34), hogfish (18), gag grouper (15), and black grouper (1).
Lane snapper averaged 17 cm long (to 22 cm), and gray snapper averaged
22 cm (to 45 cm). Ten secondary commercial species dominated numbers and
biomass as a result of tomtate (10,207 inds., ave. 16 cm), white grunt
(3,225), and bluestriped grunt (834). Adult bigeye (160 inds.) and
porkfish (102) were other common secondary commercial species.

Fourteen recreational species included the primary commercial species
along with porkfish, yellow jack (11 inds.), snook (8, ave. 4.4 kg), and
permit (3, ave. 11 kg).

Twenty-two primary marine life species included cocoa damselfish (71
inds.), bluehead wrasse (57), bicolor damselfish (51), sharpnose puffer
(35), spotfin butterflyfish (28) gray angelfish (22), blue angelfish
(21), and high hat (21). Twenty-four secondary marine life species
included striped parrotfish (190 inds.), slippery dick (97), redband
parrotfish (70), masked goby (64), spotted goatfish (46), ocean surgeon
(36), and doctorfish (32). Only 1% of individuals (8 species) had no
economic value.

4.6.7. Fishing Activity .6.7. Fishing Activity ;

Although no recreational or commercial fishing or marine life collecting
was observed at the units, the general area around Big Pine Shoal is
heavily fished by all three industries. Considering the level of use of
electronics in reef fishing, the high profile units have probably been
located and fished on occasion. A recreational fishing vessel was
observed attempting to anchor on a mid-depth unit, and a lost anchor was
removed from a deep unit. Commercial hook and line fishing for
yellowtail and gray snapper is an active fishery a short distance west
of the study area. A commercial marine life collector once worked to
within a few meters of the observer during a census on the mid-depth
natural reef, and collectors were routinely seen in the vicinity.

Wire fish traps were extensively used seaward of the reef tract in this
area for many years. Illegal usage (shallower than 30.8 m) was routine
on the deep natural reef, and traps were observed within about 15 m of
the deep units and as shallow as 26.2 m depth. Ten ghost traps (some
open, some closed) were found in the area of the deep reef. Observed in
traps were groupers, porgies, angelfishes, jacks, hogfish, gray snapper,
and others (Plate 13). Based on the level and history of use of fish
traps in this vicinity, it is probable that fish populations on the deep
natural reef, and maybe at the deep units, were altered by this non
selective harvest of larger individuals. All use of fish traps in the
southeast Florida area was banned in early 1992 by the South Atlantic
Fishery Management Council, about 1 1/2 years after cessation of
monitoring for this study.

Recreational and commercial fishing occur on both Bahia Honda and
American Shoal rubble sites. Catches of red, black, and gag groupers,
mutton, lane, gray, and yellowtail snappers, permit, snook, pompano,
sawfish, cobia, jacks, and grunts have been documented at the Bahia
Honda reefs along with diver catches of spiny lobster (J. Lapp, pers.
comm., 1992; Kruer, pers. observs.). Reported catches of *Mycteroperca*
groupers over several years included roughly 80% gags and frequent black
groupers under the 20 inch size limit (J. Lapp, pers. comm., 1992).
Visual censuses at Bahia Honda showed about 62% of *Mycteroperca*
groupers were gags and 30 black grouper with a mean length of 47 cm (19
inches), ranging 6 to 100 cm (Table 23).

Recreational and commercial catches documented at American Shoal from
1986 to 1991 included lane, yellowtail, gray, schoolmaster, and mutton
snappers, gag, yellowedge, red, and black groupers, large jewfish,
pompano, barracuda, cero, Spanish mackerel, large king mackerel.,
bluefish, tomtate, white grunt, greater amberjack, blue runner, jack
crevalle, small bonefish, bigeye, and shark (J. Lapp, pers. comm., 1992;
Kruer, pers. observs.). In May 1986, April and May 1987, and April 1988,
sexually ripe male and female lane snapper (up to 1 kg), one of few
possibly under-utilized local commercial species, were common on the
American Shoal site indicating that they may aggregate and spawn there
part of the year (Kruer, pers. observs.).

4.7. Objective Number 7. Evaluate the economics of constructing,
transporting and placing artificial habitats to enhance fishery
resources and fishing opportunities. .7. Objective Number 7. Evaluate
the economics of constructing, transporting and placing artificial
habitats to enhance fishery resources and fishing opportunities. ;

Although donated materials and labor made up a major portion of the cost
to design and construct these prefabricated units, the commercial cost
to construct such structures can be estimated. Variations in structural
design to improve fishery enhancement effectiveness (i.e. add small
spaces) probably would not appreciably alter the costs if similar
amounts of material were used. Mass production of such units would
probably result in a lower per unit construction cost. Unit
transportation costs have the most potential for reduction below those
paid in this project; per ton transportation costs were considerably
lower for rubble. A limitation on unit size, unless constructed at a
waterfront facility, is the ability to transport them via roads to a
barge staging area.

Costs associated with constructing the rubble reefs are related to
loading and transportation, both on land and water. Most work to date
has been with rubble loaded directly onto barges at a bridge removal
site, but a number of patch reefs at Bahia Honda were constructed with
large concrete debris transported by truck from several Lower Key
locations to the barge staging area. Similar reefs could be created in
the Keys to take advantage of concrete and rubble debris routinely
generated by the construction industry during reconstruction work, and
by future Florida Department of Transportation bridge removal or
rehabilitation projects. Suitable material can be stockpiled until
several full barge loads (one load is typically 200 - 300 tons, 10 - 15
truckloads) are on hand. Eliminating high costs associated with landfill
or other disposal could help offset loading and transportation costs.

Records of FKARA projects allows the following estimation of costs for
the reefs censused in this study:

4.7.1. Prefabricated Units .7.1. Prefabricated Units ;

Costs to construct 4 large units and 3 small units in 1987/88:

> PVC pipe - \$ 160
>
> poured concrete - 1,370
>
> wood forms - 267
>
> reinforcing steel - 1,068
>
> equipment rental - 190
>
> gas for torches - 85
>
> miscellaneous materials - 457
>
> transportation of donated material - 675
>
> 134 hours labor (paid) x \$12/hour - [1,610]{.underline}
>
> Subtotal - \$ 5,882

Donated - Estimated Value:

> construction yard on Big Pine Key - \$ 2,000
>
> pre-stressed beams - 10,000
>
> 225 hours labor (\$15/hour) for permitting,
>
> construction, transportation, etc. - [3,375]{.underline}
>
> Subtotal (\$ equivalent donated) - \$ 15,375
>
> Total estimated cost to construct 7 units - \$ 21,257
>
> Transportation to staging area and Alexander
>
> Marine loading and barge work (3 trips) - 12,000
>
> Total estimated cost to construct, transport
>
> and place 7 units - \$ 33,257
>
> [Cost per Unit:]{.underline} [High Units]{.underline} [Low
> Units]{.underline}
>
> Construct \$ 3,800 \$ 2,000
>
> Transport 1,700 1,700
>
> Total \$ 5,500 \$ 3,700

4.7.2. Bahia Honda Rubble Reefs .7.2. Bahia Honda Rubble Reefs ;

Eleven of the 19 patches at the Bahia Honda artificial reef (6,000 mt)
were placed from June to August, 1985 (2,700 mt), and eight were placed
from August to October, 1987 (3,300 mt). All materials were donated;
some were transported at no cost to the staging area by the Florida Keys
Aqueduct Authority and the Florida Department of Transportation, other
material was moved there by a contractor hired by the FKARA with state
grant funds.

Costs to construct the Bahia Honda rubble reefs:

1985

> Transport 90 truck loads of concrete bridge
>
> decks and rubble x \$125/load - \$ 11,250
>
> 15 Misener Marine barge trips (2,700 mt)
>
> x \$2,800/load - \$ 42,000
>
> 3 loads old Bahia, Honda Bridge steel girders
>
> 3 loads steel pipe and steel hangars
>
> 9 loads large concrete slabs/rubble
>
> FKARA miscellaneous expenses - \$ 750
>
> 100 hours of donated time x \$15/hour - [1,500]{.underline}
>
> Subtotal - \$ 55,500

1987

> 16 Misener Marine barge trips (3,300 mt) from
>
> partial removal of Spanish Harbor Bridge x \$ 3000/load - \$ 48,000
>
> FKARA miscellaneous expenses - 500
>
> 100 hours of donated time x \$15/hour - [1,500]{.underline}
>
> Subtotal - \$ 50,000
>
> Total estimated Bahia Honda Artificial Reef cost - \$ 105,500
>
> Cost per metric ton (\$ 105,000/6,000 mt) = \$ 18

4.7.3. American Shoal Rubble Reefs .7.3. American Shoal Rubble Reefs ;

Of four patch reefs at the American Shoal site (3,850 mt), patch 1 (550
mt) was placed in April, 1983; patch 2 (1,100 mt) in September, 1985;
patch 3 (1,650 mt) from September to October, 1987; and patch 4 (550 mt)
from October to November, 1987. Patches 1 and 2 are composed of large
concrete rubble from partial removal (on two occasions) of the nearby
Niles Channel Bridge and patches 3 and 4 are from the Kemp Channel
Bridge.

Costs to construct the American Shoal patch reefs:

1983

> 3 Alexander Marine barge loads x \$2,666/load - \$ 8,000
>
> FKARA miscellaneous expenses - 300
>
> 30 hours of donated time x \$15/hour - [450]{.underline}
>
> Subtotal \$ 8,750

1985

> 11 Misener Marine barge loads x \$2,800/load - \$ 30,800
>
> FKARA miscellaneous expenses - 500
>
> 80 hours of donated time x \$15/hour - [1,200]{.underline}
>
> Subtotal \$ 32,500

1987

> 12 Misener Marine barge loads x \$3,000/load - \$ 36,000
>
> FKARA miscellaneous expenses - 500
>
> 80 hours of donated time x \$15/hour - [1,200]{.underline}
>
> Subtotal - \$ 37,700
>
> Total estimated American Shoal Artificial Reef cost - \$ 78,950

Cost per metric ton (\$ 78,950/3,850 nit) = \$ 21

4.7.4. Cost Effectiveness of Artificial Reefs .7.4. Cost Effectiveness
of Artificial Reefs ;

Knowledge of the amount of concrete and steel deposited at the bridge
rubble sites allows an estimation of the area this material now covers,
and with estimated biomass density and construction costs, a comparison
of cost effectiveness to the high profile units. Bohnsack *et al.*
(1989) report that small clusters of prefabricated concrete cubes (1.75
m2 bottom area each) placed off Key Biscayne, Florida had higher fish
density than larger clusters of cubes, but found that biomass density
increased with additional cubes. Multiple prefabricated units of the
type used here, placed together, might alter standing stock of fishes at
individual units from that found here with only two units placed 50 m
apart. Multiple units might show decreased overall fish density but
greater biomass density.

Short tons placed at the rubble sites were converted to cubic yardage
using a factor of 0.541 based on the known weight of 3,750 pounds of a
cubic yard of solid concrete aggregate. Cubic yards were then converted
to cubic meters using the standard factor of 0.76. Calculating 1.2 m
(4\') as an approximate \"average\" height of the patches based on
observations, and allowing 25% open space within a patch, the American
Shoal reefs (4,200 short tons) are estimated to cover about 1,800 m2 of
bottom and the Bahia Honda patches (6,600 short tons) about 2,830 m2.

Biomass density was determined for the rubble sites by dividing the
total recorded biomass at each site by the total area censused at the
site (N x 177 m2) . American Shoal reefs showed a biomass density of 340
g/m2 and Bahia Honda showed 199 g/m2. Biomass density at the 4 high
units was determined by dividing total biomass recorded (724 kg) by the
total area censused in all high unit samples (62 x 27 m2 = 1,674 m2).
Mean biomass density at the high units was therefore 432 g/m2. In terms
of the dollar cost (see estimates above) of resulting fish biomass, the
American Shoal rubble reefs are about 3.6 times and the Bahia Honda
reefs about 2.5 times more cost effective than the high units. The
different physical influences on fish assemblages of artificial habitats
in Hawk Channel and on the reef tract may also be an important factor in
cost effectiveness in regard to fish biomass. Although the low units are
not assessed here, their cost effectiveness when compared to the rubble
reefs is considerably less than the high units.

5\. Comparisons to Other Artificial and Natural Reefs . Comparisons to
Other Artificial and Natural Reefs ;

Table 44 provides a comparison of the general results from this project
with studies by Bohnsack *et al.* (1989) using 50 2.3-m3 prefabricated
concrete modules arrayed in various numbers off Key Biscayne, studies of
a concrete module reef in Hawaii by Brock and Grace (1987), and studies
of a reef made of tires near Pacific Reef in Biscayne National Park,
Florida by Stone *et al.* (1979).

This study of Keys artificial reefs showed total species ranging from 67
to 73 on the units, and 72 to 90 on the rubble reefs. On artificial
habitats off Key Biscayne there were 74 (1 module reef) species to 96
species (8 module reefs); in Hawaii, 125 species; and at the tire reef
in Biscayne National Park, 98 species (Table 44). Total species on
natural reefs studied here ranged from 104 to 114, higher than the 81 to
85 species reported for large natural reefs in the studies compared.

Fish densities from 1.7 to 5.9 inds./m2 on artificial reefs in this
study, were higher than densities on artificial reefs in Hawaii (1.6/m2)
and Biscayne National Park (2.1/m2), but considerably lower than
densities on the concrete modules off Key Biscayne (24 - 71/m2).
Difference in sizes of artificial reefs in various projects possibly
accounts for the differences in the numbers of species, total numbers,
and densities (Bohnsack *et al.,* 1989; Ambrose and Swarbrick, 1989).
Total counts on rubble patch reefs might reflect considerably higher
fish densities than those reflected here. Fish densities on natural
reefs in this study ranged 0.9 to 1.5 inds./m2; in Hawaii density was
1.6/m2; off Key Biscayne density ranged 1.0 to 1.5/m2; but in Biscayne
National Park density was 6.8/m2 on natural reefs (8 samples).

In studies compared, biomass density was considerably higher on
artificial reefs than on natural reefs (Table 44). On the deep natural
reef studied here, biomass density was 72 g/m2, off Key Biscayne on
natural reefs it ranged from 47 to 72 g/m2, and in Hawaii it was 46
g/m2. On artificial reefs studied here biomass density ranged from 397
to 495 g/m2 on the high profile units and 199 to 340 g/m2 on bridge
rubble sites, off Key Biscayne artificial reef biomass ranged 390 to 701
g/m2, and in Hawaii it was 1267 g/m2. Total mean biomass per sample on
the high units (27 m2) here was 10.4 kg at mid-depth and 13.0 kg at deep
units, while at 8-block reefs (14 m2) off Key Biscayne mean sample
biomass was 10.2 kg. Mean fish size (biomass) was larger in the Keys
(75-126 g on high units and 34 - 91 g on rubble reefs) than off Key
Biscayne (6 - 29 g). It was largest in Hawaii (137 g). Commercial
species composed 59% of total biomass on the artificial reefs in this
study, 61% at Hawaiian artificial reefs and 61% off Key Biscayne.

Stationary visual censuses conducted in 1983 at nearby Looe Key Reef
(Fig. 4) from 0 to 10 m depth on the shallow \"fore reef\" zone
(Bohnsack *et al.,* 1987) revealed greater fish abundance and slightly
greater diversity than found at the shallow bank reef sampled here.
Recorded at Looe Key (N=160) were 116 species and about 250 individuals
per census. Here 107 species and 153 fishes per census were recorded (N
= 111). The 8 most frequent shallow natural reef species recorded here
were, in decreasing order, striped parrotfish, yellowhead wrasse,
bicolor damselfish, bluehead wrasse, blue tang, foureye butterflyfish,
ocean surgeon, and redband parrotfish. All were listed in the 15 most
frequent at Looe Key Reef. Comparing relative abundance of fishes at the
shallow reef in this study to that found at Looe Key Reef showed
harlequin bass, white, bluestriped, and striped grunts, porkfish, cocoa
damselfish, doctorfish, hogfish, high hat, saucereye porgy, and blue
angelfish more abundant at the shallow bank reef studied here. Fishes
considerably more abundant at Looe Key Reef were yellowtail,
schoolmaster, gray, and lane snappers, yellowtail, longspine, dusky, and
threespot damselfishes, sergeant major, caeasar, French and tomtate
grunts, stoplight and princess parrotfishes, spotted goatfish, bermuda
chub, Spanish hogfish, masked goby, bluehead and clown wrasses, blue and
brown chromis, glassy sweeper, and barracuda. The greater structural
diversity of the complex spur and groove forereef at Looe Key, and its
location immediately adjacent to deep waters of the Straits of Florida,
probably account for differences observed.

Until now, quantitative information on deep reef fishes of south Florida
was lacking, but Alevizon (1990) suggested that there should be strong
similarities with insular Caribbean deep reef (\>30 m) fish communities.
Based on the deep natural reef (26 to 31 m) data provided here, however,
there may be distinctive differences in these populations. Alevizon
(1990) reports that Caribbean deep reef fishes are dominated by
\"strictly carnivorous, non-schooling species\" including gobies,
basslets, squirrelfishes, wrasses, and sea basses. Here, based on
abundance and biomass, dominant families were grunts, jacks,
damselfishes, wrasses, gobies, snappers, sea basses, and angelfishes,
with grunts, jacks, and snappers often observed schooled.

6\. Conclusions and Recommendations . Conclusions and Recommendations ;

This Florida Keys study showed that large prefabricated units and
concrete rubble patch reefs, placed as artificial marine habitats on
sand bottom, greatly enhance the abundance, diversity, and biomass of
fish in an area. Densities of individuals and biomass were found
considerably higher at artificial reefs than at nearby, natural, bank
reefs, a result consistent with other studies. Location, depth, and
vertical profile are important factors determining fish assemblages at
artificial habitats in the Keys. Fishes were both produced at artificial
reefs and attracted from the surrounding area. Fish assemblages at the
Hawk Channel artificial reefs were considerably different from those on
the offshore reef tract, particularly in terms of dominant species.

Settlers at the artificial reefs were mostly of small species important
to the marine life industry, while colonizers were species important to
commercial and recreational fishermen. Many settler species were
demersal egg layers such as damselfishes, gobies, and blennies, or mouth
brooders like cardinalfishes. The isolated rubble reefs in Hawk Channel
reflected the greatest proportion (48%) of total biomass potentially
produced by settler species, probably the result of their greater
structural complexity, age, and large area. Abundance estimates were
believed conservative at Hawk Channel sites because of poor visibility
and considerable amounts of sand in census areas. Although attraction of
adult fishes from the natural reef to the prefabricated units occurred,
the regular movements of many browsers and herbivores back and forth
appeared to be mainly for exploitation of new food resources. Large
carnivores also tended to colonize these reefs temporarily, often in
schools.

Doctorfish and slippery dick were ranked in the 15 most frequent species
at all five artificial reef sites censused; only slippery dick was
ranked as one of the most abundant at all sites, and only gray angelfish
and hogfish were highly ranked at all sites based on total biomass.
Duplicate high units at the same depth shared roughly three-quarters of
the 15 most frequent and abundant species but only just over half of the
total species, reflecting the large species pool in these areas. Sets of
units and natural reefs at the same depth shared less than half of the
total species, with just over half of the total found at the units. Of
the 15 most frequent, abundant, and heaviest species, less than
one-third were shared by the units and natural reefs, probably because
of the very different structural complexity and limited food at the
units.

The high profile units, and areas of high vertical relief at rubble
reefs, allowed fish to partition space and food resources, increasing
both diversity and abundance. Fishes benefited by the additional hard
surfaces provided at all artificial reefs, both for food and cover.
Planktivores dominated fish numbers at the mid-depth and deep units and
the deep natural reef. Bottom feeding invertivores (especially grunts)
were by far the most abundant fishes at the Hawk Channel rubble sites,
indicating productive bottom feeding areas. Piscivores dominated biomass
at the mid-depth and deep units and at Bahia Honda, where groupers,
snappers, and snook were common. The influence of tidal currents
offshore from Bahia Honda Channel may be conducive to diverse and
productive benthic communities and high biomass of piscivorous fishes.
The relatively low proportion of piscivore biomass at the deep natural
reef may be the result of heavy use of fish traps. By the second year,
the deep units appeared to be somewhat predator limited, with piscivores
common (especially snappers, jacks, and barracuda), but few grunts and
*Chromis* damselfish, common groups on the deep natural reef. Biomass
density was nearly seven times and mean fish weight nearly three times
higher at the deep units than on the deep reef. Of all artificial reefs,
biomass density, was highest at the deep units.

Although fish density increased with depth on the natural reefs studied,
highest density and number of species recorded on the units was at
mid-depth. Frequent aggregations of yellowtail snapper around the top of
the mid-depth units demonstrate the ability of high profile structures
to concentrate this valuable species. Browsers and herbivores were more
abundant at the mid-depth units than at other artificial reefs. Few
parrotfishes occurred at any of the units. The development of hard
corals, and the fouling community in general, was most rapid at
mid-depth.

The simple, low, shallow units had the lowest abundance of fishes with
large nurse sharks contributing most of the biomass. Most fishes
recorded at the shallow units were of settler species valuable to marine
life collectors, pointing to the potential of shallow artificial
habitats to produce fishes for this industry.

Of all reefs studied, the rubble reefs in Hawk Channel had the highest
density of fishes and the greatest proportion of species important to
the commercial and recreational fishermen. Fish density was 3 to 5 times
higher at rubble reefs than at natural reefs. Comparison of dominant
species at rubble reefs to those at natural reefs showed highest
similarity with the shallow natural reef, the closest reef to Hawk
Channel. The two similar rubble sites in Hawk Channel shared only half
of the 15 most abundant and heaviest species, indicating distinctive
fish assemblages in different regions of Hawk Channel.

Artificial reef construction in the Keys has resulted from considerable
interest by both fishermen and divers, interest that continues to grow
as numbers of these users increase. This study shows the ability of
rubble patch reefs and high profile units to produce and concentrate
fishes economically important to fishermen and of interest to divers. In
a tourist economy, the preference of many visiting divers for diving on
sunken vessels and unusual structures, as an alternative to natural
reefs, lends incentive to the placement of artificial reefs. Species
important to the commercial hook and line fishermen comprised nearly
two-thirds of total biomass at all artificial reefs combined, as found
in other studies. At the American Shoal rubble reef, 99.2% of censused
fishes had an economic value. Artificial reefs may take on considerable
importance as people management becomes more pressing in the Florida
Keys National Marine Sanctuary, and the concept of fishery reserves is
reviewed for the South Atlantic region of the United States.

Rubble reefs, built with donated materials, were roughly three to four
times more cost effective than the high units in terms of biomass
produced and aggregated. Large concrete rubble, similar to that used in
construction of the Hawk Channel patch reefs studied here, is scattered
around the Keys at various legal and illegal disposal sites and is
routinely generated by the local construction industry. Additional
bridge removal and reconstruction planned by the Florida Department of
Transportation will also generate large quantities of concrete debris
appropriate for artificial reef construction. Modification of the Keys
marine environment through use of artificial habitats is already
widespread, including numerous small rubble piles under private docks,
thousands of bridge pilings, utility pole foundations, rip rap seawalls,
rock jetties, and illegal artificial reefs composed of various items
such as piles of trap debris, appliances, and steel drums. Properly
placed, stable, durable, hard surfaces can be of benefit to the marine
environment by providing long-term food and shelter resources; but
unstable, lightweight material can be a liability.

Because of their relatively small scale, artificial reefs are minor
contributors to the overall fish population of the extensive hard
bottoms of the Florida Keys, but their ability to enhance fish
communities in localized areas is very significant. The current high
levels of use and interest in artificial reefs in the Keys requires
serious consideration of the value and potential of additional reef
building for future management in the Florida Keys ecosystem.

7\. Recommendations for a Continuing Artificial Reef Program in the
Florida Keys . Recommendations for a Continuing Artificial Reef Program
in the Florida Keys ;

1\. Based on the documented biological enhancement that results from
properly constructed artificial reefs, and on their value as management
tools, well planned reef construction should continue as compatible with
objectives of the recently designated Florida Keys National Marine
Sanctuary (FKNMS). Artificial reef construction is appropriate only on
stable, open, sand bottom, and under no circumstances should their
placement displace or damage productive seagrass or hard bottom
habitats. Large sandy areas seaward of the reef tract, on the reef
tract, in Hawk Channel, and in the Gulf of Mexico offer ample suitable
locations.

2\. A program to build additional rubble patch reefs in the Florida Keys
should be initiated. Based on data presented here reflecting high
diversity and abundance of economically valuable fishes at rubble reefs,
Monroe County should institute a program to collect and transport
suitable concrete rubble to isolated sand bottoms in Hawk Channel,
preferably in physically active settings offshore from channels. Careful
handling and placement would assure valuable vertical relief and maximum
benefit from creation of numerous, small patch reefs. Sources of funding
include the Monroe County Boating Improvement Fund, Florida fishing
license monies administered by the Florida Department of Natural
Resources, and disposal fees paid by the construction industry and
public utilities that generate such materials. Suitable staging areas
with deep water access should be located in strategic areas of the Keys
where appropriate material can be stockpiled until an adequate amount is
on hand for barging to a permitted offshore site.

3\. Artificial reefs should be used for management of divers and
fishermen to reduce pressure on the natural reef. As a result of dive
industry interest, the sinking of additional steel vessels in open,
sandy areas offshore from the reef tract, and the placement of large,
stable, prefabricated units in shallow, clear water zones should be
considered to provide alternative diving sites. Fabricating units with
both small and large interstices for fishes would more closely
approximate natural conditions and result in even more diverse and
interesting fish assemblages. In addition, deep water (\>45 m) wrecks
could be placed for hook and line fishermen.

4\. Consideration should be given to special rules for Keys artificial
reefs. To avoid user conflicts, preclude possible overharvest, and
possibly implement no harvest zones in some locations, consideration
should be given to the concept of Special Management Zones under the SMZ
program of the South Atlantic Fishery Management Council, consistent
with FKNMS regulations. Review of artificial habitats (especially rubble
reefs) solely to increase biological production should occur, with the
idea of no harvest allowed at the site, or to the placement of such
reefs within no harvest areas.

5\. The artificial habitats studied here should be used for future
research. The stability and durability of the prefabricated units and
rubble reefs allows for long-term study of their fish assemblages. The
use of the same stationary census method on large rubble reefs placed on
sand on the reef tract off Long Key and in deep water off Islamorada in
the mid 1980\'s would allow direct comparison to the similar Hawk
Channel reefs studied here. The fish assemblages on the large steel
vessels intentionally sunk in the Keys need to be quantified and the
economic value of the vessels to the local dive industry determined.

6\. Natural reef data from the three depths censused should be used as a
baseline for future comparisons. The site specific quantitative
information herein provides a valuable baseline for evaluation of
possible changes in fish community structure over time as a result of
various management efforts (i.e. fish trap prohibition, marine fishery
reserves) and natural influences.

8\. References . References ;

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Bohnsack, J. A., D. E. Harper, D. B. McClellan, D. L. Sutherland, and M.
W. White. 1987. Resource survey of fishes within Looe Key National
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Bohnsack, J. A., D. L. Johnson and R. F. Ambrose. 1991. Ecology of
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9\. Acknowledgments . Acknowledgments ;

Support for the monitoring of all reefs and report preparation was
provided by the National Oceanic and Atmospheric Administration through
National Marine Fisheries Service MARFIN Program grant #NA89AA-H-MF179.
Land transportation and barging of the units were paid for by a grant
from the Monroe County Boating Improvement Fund with assistance of the
Monroe County Cooperative Extension Service. We thank Joan Borel of
Summerland Key for her very helpful editing of the final report. Baxter
Gentry of Sugarloaf Key and Joan Gladwell of Big Pine Key we thank for
financial contributions to the construction phase of the project. Mary
Anne Rockett of Underseas, Inc., on Big Pine Key generously provided
numerous free air fills. Terry Thommes N.S.A., an architect and sculptor
from Big Pine Key, designed and oversaw construction of the
prefabricated units for the FKARA. Capt. Fernand Braun of Little Torch
Key provided charter vessels and excellent dive support, and Bill Keogh
of Big Pine Key performed most of the photography, including some with
funding from the Monroe County Tourist Development council. Dr. Jim
Bohnsack, Project Officer, and Doug Harper of the National Marine
Fisheries Service, Southeast Fisheries Center in Miami provided computer
programs and technical support along with John Hunt of the Florida
Department of Natural Resources Marine Research Institute in Marathon,
Florida.

\[Rescue of this work in 2005 was funded through a grant of the South
Florida Ecosystem Restoration Prediction and Modeling Program (SFERPM) -
a competitive program conducted by the Center for Sponsored Coastal
Ocean Research (CSCOR), in association with the South Florida Living
Marine Resources Program (SFLMR) - for Coastal and Estuarine
Data/Document Archeology and Rescue (CEDAR) for South Florida.\]

[^1]: ^∆^ PO Box 420334, Summerland Key, FL.

[^2]: ^◊^ Rt. 5, Box 678, Big Pine Key, FL.