BULLETIN OF MARINE SCIENCE, 37(1): 3-10, 1985
USE OF MAN-MADE REEFS TO CONCENTRATE
SNAPPER (LUTJANIDAE) AND GRUNTS (HAEMULIDAE)
IN BAHAMIAN WATERS
By
William S. Alevizon, Jonathan C. Gorham,
Rebecca Richardson and Sheryl A. McCarthy
ABSTRACT
The feasibility of using man-made reefs to concentrate populations offood fishes (Lutjanidae and Haemulidae) was investigated in Bahamian waters. Fourteen reef units, constructed
of PVC pipe and concrete blocks, were installed in seagrass beds and sand bottom habitats
at depths of 4-5 m in July of 1982. The units were highly successful in attracting the target
species, and appear to offer a promising method of substantially increasing the readily available protein supply for islanders throughout the Caribbean at a relatively low cost. Comparisons of the fish communities associated with natural patch reefs and man-made reefs in
both habitats suggest that reef structure is subordinate to source of recruitment as a determinant of reef fish community structure.
Islanders throughout the world traditionally depend heavily on their fishery
resources for protein. Although Caribbean reef systems are typically populated
by hundreds offish species, relatively few of these fishes are of sufficient size, food
quality, and catchability to be profitably harvested for food. Thus, the problem
of providing adequate protein for the increasing human populations of Caribbean
islands has become of considerable concern.
Two groups of fishes which appear to offer the promise of representing an
increased contribution to the protein needs of Caribbean islanders are certain
grunts of the genus Haemulon and snappers of the genus Lutjanus. These fishes
are common in inshore lagoonal waters of the Caribbean, wherever small coral
heads, rock outcroppings, or man-made objects (e.g., old automobiles, etc.) provide structural complexity to the substrate. Such features are utilized as shelter
areas during the day, when fish congregate in large numbers. At night, grunts and
snappers leave their daytime shelter to feed on a wide variety of small invertebrates
found in the sand and seagrasses which surround the occasional reefs. The movement patterns and foraging behavior of some of these grunts have been well
documented (McFarland et al., 1979), and the habits of certain of the snappers
appear to be highly similar. Because the "home reef' is used only as a shelter site
during times of inactivity, its composition and structure can vary widely and still
be acceptable to these fishes. This makes the use of artificial reefs in the mariculture
of these fishes a highly promising endeavor, since suitable shelter is apparently
the major limiting resource.
The main objective of this research was to investigate the possibility that small
man-made reefs might represent an efficient and economical means of providing
harvestable quantities of high quality food fishes (snappers and grunts) in a variety
of inshore habitats in the Bahamas. Man-made reefs of varying composition and
structure have been placed in marine habitats throughout the world during the
last 20 years, and have generally proven effective at concentrating fishes. However,
the types and numbers of fishes attracted have varied widely. In almost every
such venture, the primary object has been simply to provide fish habitat; the reefs
were not "targeted" for particular species through siting and/or design. Thus, our
approach differs from most previous efforts in one major aspect: our intent was
3
4
BULLETIN OF MARINE SCIENCE, VOL. 37, NO. I, 1985
LITTLE
BAHAMA
BANK
x
X
X
.-.....
:.:.....
'::;':;:;:';;'{;:i:
.:::;:.
N
i
NORTH
WEST
PROVIDENCE
CHANNEL
X artificial
reefs
~~
grass beds
::,:,:,::,:,:,,,,,,:
cor a Ire e f s
Figure I.
The research area, located at the eastern end of Grand Bahama Island (26°3S'N, 77°S0'W).
to develop reefs designed and located so as to attract and support maximum
populations of a few selected species. We investigated the effects of reef size and
siting on fish population growth and eventual community structure attained.
Additionally, we compared community structure of fishes inhabiting small natural
reefs with that attained on man-made units sited in the same areas.
METHODS
All field work was conducted in waters near Deep Water Cay, located at the eastern end of Grand
Bahama Island (Fig. I). The area is relatively isolated with minimal human activity, and the full range
of Caribbean island inshore habitat-types is readily accessible, including extensive coral reef systems,
mangroves, seagrass beds, and sand flats.
Field testing of man-made reefs began in early July 1982. Individual reef units were constructed of
12 standard concrete building blocks and PVC pipe (Fig. 2a), and could be installed in combination
to provide a variety of reef sizes and configurations. PVC subsections were assembled onshore, and
final reef assembly was accomplished on site by a team ofthree workers. Reefs were built and installed
at a rate of about one reef unit per day. Scuba was helpful for reef installation, but not necessary.
By the end of July, 14 reef units were deployed. These were arranged in configurations of one, two,
and four units per reef. A set of all three configurations was installed in lagoonal seagrass beds about
2 km seaward and west of Mclean's Town, Grand Bahama, and another set installed on a mainly
sandy substrate about 4-6 km offshore ofSweetings Cay on the Little Bahama Bank (Fig. I). The two
siting areas differed in several major respects. In addition to the difference in the nature ofthe substrate
(sand versus seagrass), the reefs sited off Mclean's Town were within 100 m of the inshore margin
of an extensive natural fringing reef system. In contrast, the units sited on the Little Bahama Bank
were about 8-10 km from the nearest extensive natural reef. The two areas communicate by means
of shallow tidal creeks which run through extensive mangrove areas (Fig. I). This arrangement allowed
for the assessment of the effects of differing reef size and siting on the recruitment of fishes.
Recruitment was documented by visual censusing of the reefs, beginning shortly after their instal-
ALEVIZON ET AL.: MAN-MADE REEFS IN BAHAMAS
210
LAGOONAL
GRASSBEOS
27'
LITTLE
BAHAMA
5
BANK
03.
70
'00
'00
00
'00
TIMElOAY91
Figure 2.
Bahamas.
Population growth of fishes on man-made reefs sited in two habitats near Deep Water Cay,
lation. The small size and shallow depth of the reefs allowed a snorkeler to accurately census all but
the very small or cryptic fishes. Censuses were repeated periodically for approximately I year after
installation, when fish populations had presumably approached equilibrium densities and community
structures (Nolan, 1975; Stone et aI., 1979; Bohnsack and Talbot, 1980).
The fish communities observed on the man-made reefs about 1 year after installation were compan:d
with those inhabiting comparably sized and sited natural patch reefs. A total of 42 small patch reefs,
ranging in size from approximately 0.65 to 13.5 m2 in area were investigated. Twenty-eight of
these occurred on the Little Bahama Bank, about 1-3 km offshore. Fourteen occurred in the lagoonal
seagrass habitat adjacent to a fringing reef. Thus, the natural reefs investigated were located in areas
comparable (in terms of habitat-type and distance from the main reef system) to those in which manmade units had been installed.
Figure 3. (A) Installed two-unit reef, Little Bahama Bank (July 1983). (B) Standing stock of fish at
man-made reef sited in lagoonal seagrass beds (December 1982,4.5 months after installation). Standing
stock of fish at man-made reef, Little Bahama Bank (March 1983, about 9 months after installation)_
6
BULLETIN OF MARINE SCIENCE, VOL. 37, NO. I, 1985
~
~
~
w
120
m
100
LAGOONAL
OAASSBEOS
LITTLE
BAHAMA
BANK
W
o
::
••
80
2
UNIT
1 UNIT
•• UNIT
20
40
eo
120
180
200
2-40
280
320
300
40
eo
120
100
200
2'0
280
320
380
T1MEIOAYS)
Figure 4. Population growth of target fishes (snappers and grunts) on man-made reefs sited in two
habitats near Deep Water Cay, Bahamas.
Field investigation of the natural patch reefs involved two distinct aspects: censusing of resident
fish communities, and measuring of reef size and structure. Fish censusing was accomplished by a
snorkeler who took a single visual count of all fishes found in the immediate vicinity of the reef. Four
measures of reef size and structure were taken on each reef censused. An estimate of surface area was
generated by converting a measurement of maximum circumference into the surface area of a hemisphere. To define vertical development, an index was calculated by dividing the maximum height
(vertical distance from the substrate to the highest point on the reef) by the total surface area (estimated
as described above). This index reflects differences in reef shape, since reefs of the same height but
different diameters would generate correspondingly different values. A rugosity index, indicating the
degree of surface texture, was generated after the method of Luckhurst and Luckhurst (1978). The
degree of undercut reflects the presence of caves and ledges near the base of the reef, necessary
microhabitats for some species. It was expressed as the ratio of the circumference at the level of the
substrate to the maximum circumference. The obtained values of each of these measures/indices were
found to approximate a normal distribution within each habitat. Thus, reefs from the two habitats
were tested for significant differences in these characteristics by Student's (-test.
RESULTS
Recruitment of marine organisms on the man-made reefs was rapid. The first
arrivals (fish and sea urchins) were observed within 48 h of reef installation. Major
differences in the pattern of fish recruitment were apparent between units placed
in the two habitats (Fig. 3). Whereas fish populations reached maximal levels in
50-60 days on the lagoonal grassbed reefs, two of the three reefs sited on the
Little Bahama Bank continued to display marked increases in resident fish populations throughout the 12-month study period. The recruitment of sessile plants
and animals, as well as mobile invertebrates (e.g., gastropods, sea urchins, crabs
and spiny lobster) also generally occurred very rapidly throughout the summer
and early fall, with a decreased rate evident during the late fall and winter. The
growth of fish populations and epibiota on the structures was photographically
documented in Figure 2. Although the prototype reef was not designed with special
provisions for attracting spiny lobster (Panulurus spp.), these were observed occasionally on the reefs throughout the study. They appeared to take up residence
for a short while, and then move on. The maximum number observed in a single
census was 24 (four-unit reef, Little Bahama Bank).
The reefs were highly successful and efficient in attracting the target species
(Fig. 4). Regardless of location or configuration of the reefs, snappers and grunts
formed the overwhelmingly dominant component of the fish fauna observed
throughout the monitoring period. Target fishes comprised over 90% of all fishes
inhabiting the man-made reefs sited on the Little Bahama Bank at years end, and
from about 45% to 75% on reefs sited in the lagoonal seagrass habitat. Both
juveniles and adults appeared early, and were evident throughout.
ALEVIZON
ET AL.: MAN-MADE
REEFS
7
IN BAHAMAS
Table 1. Diversity of fishes observed on natural and man-made reefs near Deep Water Cay, Bahamas
(data from man-made reefs represents the results of censusing resident fish populations 12 months
after installation)
Number
species
observed
Seaward grass beds
Family
Acanthuridae
Apogonidae
Balistidae
Carangidae
Chaetodontidae
Diodontidae
Holocentridae
Labridae
Lutjanidae
Mullidae
Muraenidae
Orectolobidae
Pomacentridae
Haemulidae
Scaridae
Scianidae
Serranidae
Sparidae
Synodontidae
Sphyranidae
Tetradontidae
Community parameters
Species diversity (H')
Species richness (S)
Species evenness (J')
Natural
(N = 28)
Little Bahama Bank
Man·made
(N
3)
=
Natural
(N=
14)
Man-made
(N
3)
=
I
2
2
I
I
3
6
I
I
I
I
2
3
3
I
I
I
2
2
I
2
5
I
4
I
2
2
I
2
5
2
I
2
I
I
2.45
28
0.74
2.16
22
0.70
1.66
25
0.51
1.07
8
0.51
The efficiency of the units in attracting grunt and snapper appeared to be unrelated to overall reef size (i.e., arrangement into one-unit, two-unit, or four-unit
reefs). Grunts recruited were mainly the white grunt, Haemulon plumieri and the
bluestriped grunt, Haemulon sciurus. The majority of snapper recruited were the
grey snapper, Lutjanus griseus and the lane snapper, Lutjanus synagris. After I
year of recruitment, the density of target fishes ranged from 40 to 62 per reef unit,
with an estimated average weight of 0.5 to 0.7 kg per fish. The single exception
to this trend occurred on the one unit reef sited in the lagoonal grassbeds, on
which 113 target fishes were counted in the final census. However, the discrepancy
was due entirely to a school of 51 small ( < 100 mm standard length) lane snapper
which had taken up residence since the prior (March 1983) census.
The location of the reefs resulted in three notable differences in terms of recruitment of fishes. First, the initial recruitment rate was much higher on the
lagoonal grassbed reefs, although after about 8 months the target fish population
sizes, on a per reef-unit basis, were equitable on all reefs (Fig. 4). Secondly, the
number of species observed on the lagoonal grassbed reefs was considerably higher
(Table I). Finally, the target species composition differed somewhat with location,
with snappers generally representing a larger proportion of adult target fishes on
the Little Bahama Bank reefs. The first two effects of location (more rapid recruitment and higher diversity of lagoonal grassbed units) are most likely attributable to the relative proximity of the lagoonal grassbed units to extensive natural
8
BULLETIN OF MARINE SCIENCE, VOL. 37, NO. I, 1985
Table 2. Comparison of four structural characteristics of patch reefs in two different habitats near
Deep Water Cay, Bahamas (the means of each measure were compared by Student's t-test)
Measured values
Structural
characteristic
Area (m2)
Surface rugosity index
Vertical development index
Degree of undercut index
Lagoonal grassbeds
(N = 14)
x (±SE)
Lillie Bahama Bank
(N = 28)
x (±SE)
2.84 (±0.859)
1.28 (±0.038)
62.6 (±20.l8)
0.85 (±0.022)
2.09 (±0.205)
1.26 (±0.035)
43.6 (±5.71)
0.90 (±0.03I)
p
1.09
0.35
1.13
1.06
>0.10
>0.10
>0.10
>0.10
reef areas, which serve as the main source of recruitment. The final difference
(proportion of snappers) may be due to differences in the behavior and/or ecological requirements ofthe two families of target species. This same general result
was also evident on the natural reefs (Table I).
The size and structure of the natural patch reefs investigated in both habitats
were found to be highly similar. Significant between-habitat differences could not
be detected in any of the four measures utilized for these comparisons (Table 2).
The composition and diversity characteristics of the fish communities recruited
to the man-made reefs, and those found on the natural patch reefs, are compared
in Table 1. In general, the community structure and diversity of fishes inhabiting
man-made and natural reefs sited in the same habitat appear more similar than
do those characteristics of the fish communities associated with either type (manmade or natural) compared among habitats. The overall fish diversity (H') and
species richness (S) appeared considerably higher on the natural (as compared
with man-made) patch reefs on the Little Bahama Bank. However, it must be
kept in mind that these diversity characteristics were calculated on very different
sample sizes (number of reefs censused). Increased sample size would be expected
to primarily affect the species richness component of diversity, which is where
the major discrepancies occurred. The evenness component (1') is identical for
both types of reefs from the Bank habitat, and nearly identical for both types
from the seagrass habitat, despite the differences in sample sizes. Similarity in the
structures of the fish communities inhabiting the man-made and natural reefs was
quantified by the Bray-Curtis similarity index (Clifford and Stephenson, 1975),
which is relatively insensitive to differences in sample size. These results (Table
3) support the conclusion that the fish communities of man-made and natural
reefs sited in the same habitat were more similar than those of either type compared among habitats.
DISCUSSION
Man-made reefs, suitably sited, appear to offer a promising means of substantially increasing the availability of high quality protein for islanders throughout
the western Atlantic region. The present investigation was concluded before the
sustainable yield of the units could be empirically determined. Nonetheless, the
standing stock and recruitment data obtained indicate that units sited reasonably
close to extensive natural recruitment sources (e.g., fringing reefs) might be expected to sustain harvests of 20 or more adult target fish/month, with an average
weight of 0.5-0.7 kg/fish. The initial cost of raw materials needed to build our
reef units was about $70/unit. If the cost of whole fresh fish is taken to be $2/lb
9
ALEYIZON ET AL.: MAN-MADE REEFS IN BAHAMAS
Table 3. Similarity of community structures of reef fishes residing on man-made and natural patch
reefs near Deep Water Cay, Bahamas [similarity, compared by habitat and reef type, is quantified by
the Bray-Curtis index of similarity (IS)]
Comparison
By habitat (Little Bahama Bank ys. grassbed)
Natural patch reefs
Man-made reef units
By reef type (natural vs. man-made)
Lagoonal grassbeds
Little Bahama Bank
IS
0.55
0.62
0.65
0.75
(retail), a harvest of 20 Ib/month would represent a continuing return valued at
about $40/month. The occasional harvesting of spiny lobster would represent an
additional return.
Further research will be required to establish the long term effectiveness of such
man-made reefs deployed in large numbers. The dynamic interactions between
natural and man-made reefs are poorly understood, and conflicting information
is present in the current literature. For example, Stone et a1. (1979) built a 500tire reef close to a comparably sized natural reef off south Florida and concluded
(p. 11) that, "the artificial reef ... did not diminish the resident population of
the natural reefby attracting them to the new habitat. Most ofthe resident species
... were recruited to the artificial reef as juveniles." In contrast, we found that
the majority of recruits to our man-made units were adults, presumably recruited
(in the lagoonal grassbed habitat) from the nearby fringing reef and/or mangrove
areas.
It must be kept in mind that the long term productivity of man-made reefs in
the context investigated here is predicted on the unverified assumption that as
fishes are recruited, the recruitment source is capable of replacing its losses at a
comparable rate. Large recruitment pools (from areas such as extensive fringing
reefs) may be able to sustain high recruitment rates to many man-made units,
whereas more restricted recruitment pools (such as those associated with isolated
patch reefs) would be expected to sustain correspondingly lower rates of recruitment. In this context, it is worth noting that McFarland (1983) documented the
semi-lunar influx of post-larval grunts (Haemulon flavolineatum) on patch reefs
off St. Croix, U.S. Virgin Islands. If the regular loss of adults from such areas
correspondingly increases the survival and possibly growth rates of this regular
supply of young, it seems plausible that for some fishes, sizable "losses" from a
natural recruitment source might be quickly replaced in tropical reef situations.
Clearly, this is an area where further research is badly needed.
The role of reef structure as a determinant of community structure of resident
reef fishes has been emphasized by some authors (Risk, 1972; Gladfelter and
Gladfelter, 1978; Gladfelter et a1., 1980). Others have tended to view reef structure
as playing a relatively minor role in comparison to the process of recruitment
(Russell et a1., 1974; Sale and Dybdahl, 1975; Sale, 1978; 1979; 1980). Our results
strongly support the latter view. The vast differences in structure between the
natural and man-made units appeared clearly subordinate to siting (i.e., nature
and distance of the major recruitment source) in determining reef fish community
structure. This point is emphasized as it is of major interest to the rapidly increasing use of man-made reefs as fish attractants.
10
BULLETIN
OFMARINESCIENCE,
VOL.37, NO. I.
1985
ACKNOWLEDGMENTS
The authors wish to thank Mr. and Mrs. Perkins Sams, whose generosity made this work possible.
We also thank the Bahamian government for permission to conduct this research.
LITERATURE
CITED
Bohnsack, J. A. and F. H. Talbot. 1980. Species-packing by reef fishes on Australian and Caribbean
reefs: an experimental approach. Bull. Mar. Sci. 30: 710-723.
Clifford, H. T. and W. Stephenson. 1975. An introduction to numerical classification. Academic
Press, New York. 299 pp.
Gladfelter, W. B. and E. H. Gladfelter. 1978. Fish community structure as a function of habitat
structure on West Indian patch reefs. Revista de Biologica Tropical 26: 65-84.
---,
J. Ogden and E. H. Gladfelter. 1980. Similarity and diversity among patch reef fish communities: a comparison between tropical western Atlantic (Virgin Island) and tropical central
Pacific (Marshall Islands) reefs. Ecology 61: 1156-1168.
Luckhurst, B. E. and K. Luckhurst. 1978. Diurnal space utilization in coral reef fish communities.
Mar. BioI. 49: 325-332.
McFarland, W. N. 1983. Periodic recruitment of French grunts, HaemulonjIavolineatum.
from the
offshore plankton. Abstract Vol. 63rd Annual Meeting Amer. Soc. Ich. and Herp., Tallahassee,
Horida. P. 22.
--,
J. C. Ogden and J. N. Lythgoe. 1979. The influence of light on the twilight migrations of
grunts. Env. Bio. Fishes 4: 9-22.
Nolan, R. S. 1975. The ecology of patch reef fishes. Ph.D. Thesis, Univ. of California. 230 pp.
Risk, M. J. 1972. Fish diversity on a coral reef in the Virgin Islands. Atoll Research Bull. 153: 16.
Russell, B. c., F. H. Talbot and S. Domm. 1974. Patterns of colonization of artificial reefs by coral
reef fishes. Pages 217-225 in Proceedings of the 2nd International Symposium on Coral Reefs,
Vol. I. Great Barrier Reef Committee. Brisbane, Australia.
Sale, P. F. 1978. Coexistence of coral reef fishes: a lottery for living space. Envir. BioI. Fishes 3: 85102.
---.
1979. Recruitment, loss, and coexistence in a guild of territorial coral reef fishes. Oecologia
42: 159-178.
---.
1980. Assemblages of fish on patch reefs-predictable
or unpredictable? Env. BioI. Fishes
5: 243-249.
--and R. Dybdahl. 1975. Determinants of community structure for coral reef fishes in an
experimental habitat. Ecology 56; 1343-1355.
Stone, R. B., H. L. Pratt, R. O. Parker, Jr. and G. E. Davis. 1979. A comparison offish population
on an artificial and natural reef in the Florida Keys. Mar. Fish. Rev. 41(9): I-II.
DATEACCEPTED: August 6, 1984.
ADDRESS: Department of Biological Sciences. Florida Institute of Technology. Melbourne, Florida
32901.