Programme for the Placement of Reef Balls ®

 

 

 

(Adopted from Literature Review: Design & Management of Artificial Reefs in the Tropics by Mr. Jamie C White)

 
(Reef Balls are copyrighted internationally.   See www.artificialreefs.org for more information on all the different Reef Ball styles including Layer Cakes, Thickets, Coral Transplant Adapters, Clover Leaves and other cutting edge designs.  Reef Balls can only be sold by Authorized Reef Ball Contractors or they can be made by licensed Reef Ball mold owners)
Programme for the Placement of Reef Balls

 

Coral reefs, by the virtue of their efficient biological recycling, retention of nutrients and provision of sheltered habitat to a variety of aquatic organisms, provide one of the most diverse and biologically productive ecosystems. Reef building corals are calcium depositing animals building colonies for numerous microscopic organisms mainly polyps. Each polyps has living plant cells, inside them, and during day time these cells phosenthesise and produce by products which are consumed by corals as food. Polyps secrete calcium carbonate which provides shelter to polyps and add to the structure of the existing colony. Several algae species thrive in calcified environment providing additional binding and adding to the beauty of reefs.

 

Coral reefs are very dynamic and fragile ecosystem, particularly vulnerable to extreme natural phenomenon and human activities. Corals have very specific environmental requirements such as light, temperature, water clarity, oxygen and salinity. Oceanographic features such as currents and wave actions also play a role on the life-cycle of corals. In Qatar, coral reefs are, shallow and of low diversity, found along the eastern coast. Coral reefs play an important role in the marine environment by providing nutrients, shelter and breeding grounds to various fish, shellfish (mollusks and crustaceans), turtles and algae.

 

Although, during the construction of Ras Laffan Port and the associated infrastructure, coral reefs were impacted, since then a gradual increase in the coral re-generation is observed. To enhance reef coverage around Ras Laffan a programme for the placement of artificial reef (Reef Balls) has been initiated.

 

 

Benefits of Artificial Reef (Reef Balls)

 

Providing hard, consolidated substratum for encrusting benthic organisms.  The majority of artificial reefs are placed in areas dominated by unconsolidated substrata (i.e. sand, mud or rubble), which support a relatively low level of productivity (Wells et al. 1985; Clark and Edwards 1994).  As the majority of encrusting benthic organisms require hard consolidated substrata for larval settlement, artificial reefs promote benthic productivity in an otherwise inhospitable environment (Schuhmacher 1988; Abelson et al. 1993). Encrusting organisms can then act as food and attractants to a diverse array of marine fauna (Fitzhardinge and Bailey-Brock 1989; Ch’ng and Thomas 1991); Increasing habitat complexity, i.e. provides shelter in otherwise “simple” habitats. Abundance and diversity of motile organisms, and to a lesser extent sessile organisms, is positively correlated to shelter availability within a reef’s structure (Hixon and Beets 1989; Borntrager and Farrell 1992;  Eggleston et al. 1992) and increased topographic complexity which allows vertical zonation (Grigg 1994); and  

Modification of local currents and eddies.   Lee-side eddies and changes in local current direction, which are induced by artificial reefs, can aid in attracting pelagic fish species (Motett, 1985) and influence the settlement patterns of encrusting benthic organisms (Abelson et al, 1993).   Artificial reefs have also been used to divert deep nutrient-rich currents up into the euphotic zone in order to enhance local primary and secondary productivity (Motett 1985; Duedall and Champ 1991).

 

 
Reef Construction Material

 

Four criteria are normally used when evaluating the use of any material that will be used to construct artificial reef: Function, Compatibility, Stability and Durability (Lukens 1997).

 

Function – The material used can contribute significantly to artificial reef ecological function, such as stimulating or inhibiting the growth of desired species.

Compatibility – Materials should be selected that ensure compatibility with the desired goals of the project. 

 

Stability –

 

Physical: The materials chosen to build an artificial reef should not allow movement of the individual structures used.  Movement can affect reef viability as well as create navigation hazards.  Anchoring systems should not be relied upon as these may fail in the long-term. 

Chemical: Chemicals contained within the material of choice must not adversely affect the success of the project or adjacent natural systems.  For example, immersion in sea water combined with ion exchange (i.e. Na+ and Cl-) can leach metals and other compounds from the materials chosen.  These may then act as anti-fouling compounds, inhibiting recruitment of essential organisms or facilitating bioaccumulation. Coral recruitment to artificial reefs constructed from scrap tyres is significantly less than to concrete or steel surfaces (Fitzhardinge and Bailey-Brock 1989; Ch’ng and Thomas 1991). This suggests that leaching of settlement inhibitors from tyres occurs (Evans 1997). 

 

Durability – Materials used must be resistant to deterioration from UV light, wave action (direct force and vibration) and corrosion.  Durable materials will maintain the desired structural design and have long life expectancy.  Fitzhardinge and Bailey-Brock (1989) found car bodies in Texas had totally disintegrated after 3-5 years, leaving the engine blocks to litter the seascape.  They could find little encrustation on the engine blocks.

 

Materials used for artificial reefs can be divided into two categories: Secondary Use and Purpose Built.  Secondary Use refers to scrap materials that are no longer required for their original purpose and can now be used for a secondary role, i.e. that of constructing artificial reefs.   Commonly known materials are shipwrecks and old oil platforms, but other materials from car bodies to old toilet cisterns have been used.  Purpose Built materials are those used in purpose designed structures.  Significant advantages are realised by using Purpose Built reef units.  They can be deployed in any quantity, profile and pattern required to achieve the desired results. 

 

 
Concrete

 

Concrete has demonstrated a high success rate as artificial reef material (Lukens 1997).  In comparison to other materials, purpose built concrete reefs tend to have a higher fish abundance (Chua and Chou 1994) and are rapidly encrusted by algae, corals, tunicates and other encrusting benthic organisms (Clark and Edwards 1994).  A significant factor in the success of concrete structures is the high calcium content. Lime, which is a significant portion of the material within concrete, is a mixture of calcium hydroxide and calcium salts.  Natural reef rock is comprised of two crystalline forms of calcium carbonate, aragonite and calcite.   This similarity in composition that concrete shares with natural reef substrates results in a high degree of compatibility for concrete by reef organisms as well as durability within the marine environment.

 

The American Society of Testing Materials in the Designation Standard Specifications for Portland cement has used five classes to describe the various grades of cement available.  Type 1 Portland cement is not suitable for marine applications, as it will deteriorate quickly under attack from sulphates, carbon dioxide and magnesium ions.  Typical seawater at 35 g.kg-1 total salinity contains on average 2.7 g.kg-1 SO42-, 0.14 g.kg-1 HCO3- and 0.41 g.kg-1 Mg2+ (Stumm and Morgan 1981).  Type II Portland cement can be expected to provide a life expectancy in the marine environment of 20-35 years, although higher grades of concrete using Type V Portland cement should be used for longer life expectancies (Lukens 1997). 

 

“Green” concrete typically has a pH of 10-11, which is significantly above the normal pH range of marine environments (~pH 8).  This caustic surface can significantly inhibit recruitment of encrusting organisms until the surface has “conditioned”, which may take up to 12 months. To counter this, pozzolanic materials can be used to neutralise the surface pH, with the added bonus that it can also improve the bonding between aggregates, thereby promoting long-term structural integrity of the units. Pozzolanic materials include ash by-products, diatomaceous earth, clays, shales, pumicites and micro-silica (Lukens 1997).

 

The use of ash by-products as construction materials in artificial reefs is seen as a viable management option for both enhancing fisheries and managing a significant waste problem.  The use of cement stabilised ash by-products was first developed by USA regulators in the 1970's Coal Waste Artificial Reef Program. Ash by-products that have been used to construct artifical reefs include coal fly ash, flue gas desulphurisation gypsum, boiler slag, municipal waste ash and oil incineration ash.

Metal bioaccumulation is a major risk of marine waste disposal, potentially causing a range of lethal (i.e. acute and chronic) and sub-lethal effects (e.g. decreased fecundity, impaired motility, endocrine inhibition).  Uptake can occur via a number of pathways.  For example, metals can be incorporated into corals by substitution of dissolved metal species for calcium, trapping of particulate (detritus) matter within skeletal cavities and uptake of organic matter from coral feeding (Fallon et al. 2001).  For many motile species, dissolved metal uptake via the gills is the most common pathway (Simkiss 1998).  However, the majority of sessile reef fauna are filter feeders, so that ingestion of particulate metals via endocytotic routes is also a major uptake pathway (Simkiss 1998).  

 

It is important to note that the larval stages of many benthic and epibenthic organisms rely heavily on chemosensory cues when selecting settlement sites and can distinguish potentially suitable settlement substrata from unsuited substrata (Morse and Morse 1996).  For example, it is known that larvae of cnidarians possess specialised sensory organs that enhance their ability to select suitable sites for settlement (Maida et al. 1994).  Larvae of the scleractinian coral Agaricia agaricites settle primarily on coralline algae (e.g. Paragoniolithon typica), with very little settlement on bare rock and none on filamentous algae (Carlon and Olson 1993).  If a particular substratum is unsuited, the larvae will continue with its search until either suitable substratum is located or the larvae dies. 

 

 Design of Reef Balls

 

The diversity of species that recruit to reef habitats is positively related to its physical complexity (Chabanet et al. 1997).  Increased complexity provides a greater diversity of ecological niches to be exploited by different species and potentially allows for zonation within a habitat, further increasing species diversity (Grigg 1994).  Research into artificial reefs has identified physical complexity (e.g. volume, void space, surface angle and surface roughness) as a major component of both community diversity and productivity (Motett 1985; Duedall and Champ 1991; Hair and Bell 1992).

 
 
Surface Roughness

 

It is known that larvae of most benthic organisms possess specialised tactile organs that enhance their ability to select suitable sites for settlement.  Work on the scleractinia has demonstrated that the success of coral settlement is partially dependent upon the level of irregularities of the chosen substratum (Maida et al.1994).  The correct surface texture is required for corals to form an attachment to the surface and undergo metamorphosis (Richmond 1997).  

At the macro scale, surface irregularities can promote survival of juvenile organisms by protecting them from algal grazers. As herbivores such as echinoderms and scarids graze on algae, newly settled juvenile corals are incidentally removed. On the Great Barrier Reef, coral recruitment was found to be 5-7 times greater when fish were excluded i.e. grazing pressure was reduced (Sammarco 1985).  Encrusting organisms that settle in depressions or on the edge of small cavities gain some protection form incidental grazing until they have grown sufficiently to gain refuge in size.  Reef Balls®  use a special technique to create an ideal surface texture for settlement by corals. (Barber 2003)

 

 
Surface Angle

 

Protection from predators is also afforded to benthic organisms that have settled on underside surfaces, such as the roof of voids.  Settlement of coral larvae occurs preferentially on lower surfaces of plates, resulting in an aggregated distribution near the underside edge.  This location provides a balance between exposure to currents and ambient irradiance as well as protection from sedimentation and predators (Fisk and Harriot 1990; Tomascik 1991; Maida et al. 1994). 

Horizontal surfaces maximise sedimentation processes, which can severely inhibit recruitment of encrusting benthic organisms.  Coral recruitment studies using settlement plates on reefs impacted by terrestrial runoff has shown that whilst slightly elevated sedimentation rates (e.g. 10-100mg.cm-2.d-1) inhibit coral recruitment, algae, tunicates, bivalves and barnacles can still survive.  However, under severe sedimentation rates, all encrusting growth is prevented on the horizontal surfaces of settlement plates, leaving only the underside or vertically oriented surfaces available for recruitment (J. White, unpubl.).  This highlights the importance of having a range of surface alignments on artificial reef units, especially if the hydrodynamic regime is low energy (i.e. no current to wash sediment away) and sedimentation rates are elevated. 

 

Vertical sides on artificial reef units can also increase turbulent flow, which produce sounds and create stagnation zones and lee waves that attract pelagic species (White et al. 1990).

 

 

 

 

 

 

 

 

 

 

 

 

 

 


Reef Balls ® avoid horizontal surfaces and provide ideal surfaces for settlement throughout the unit. (Barber 2003)

 

Volume and Void Space

 

The diversity of the non-coral community that recruit to reefal habitats is positively related to the physical complexity of the site (Hixon and Beets 1989; Chabanet et al. 1997).  Increased complexity provides a greater diversity of ecological niches to be exploited by different species and potentially allows for zonation within a habitat, further increasing species diversity (Grigg 1994).  Physical complexity (e.g. profile, volume, void space) is a major component of both community diversity and productivity (Motett 1985; Duedall and Champ 1991, Hair and Bell 1992).  

 

The size of available void spaces within each reef unit determines the residents that can shelter within a reef system (Sherman et al. 1998).  For example, small cryptic fauna (e.g. decapods) will avoid large open voids that can be occupied by larger predators such as serranids and muraenids.  Conversely a lack of large voids will preclude these larger predators as well as some grazers that require refuge at night (e.g. scarids).  A comparison of fish assemblages associated with artificial reefs containing different void sizes in Singapore showed smaller cavities restricted the size of fishes sheltering there, thus only juveniles and smaller adults were observed.  Whilst excluding the larger fishes, greater protection was provided for the smaller-sized fishes.  More open designs allowed the larger species room to manoeuvre within the modules, but inhibited smaller individuals (Chua and Chou 1994). 

 

The volume of each artificial reef unit must be considered in terms of:

·         Ability to move individual units to their final location  - availability and capacity of cranes/davits, transport, air bags, etc. 

·         Smaller units result in less void space being formed.  Void space should be maximised but not at the expense of overall unit strength or durability.

·         Larger units allow the incorporation of a variety of void sizes and shapes.

·         Larger units allow steeper and higher profiles.

 

 


 

 

 

One of 11 styles of Reef Ball artificial reef units (W 1.83m, H 1.37 m; Reef Ball web site).

 

 

 

 

 

Design of the Artificial Reef System

 

The design used for an artificial reef system will determine its cost, biological effectiveness, durability and general performance.  Factors that must be considered during the feasibility stage are horizontal spread, spacing and topographical complexity.

 

Horizontal Spread 

 

The total biomass that an artificial reef can support is directly related to the quantity and quality of effective surface area available for colonisation.  This is particularly important if the project goal is to create a low profile benthic reef, as the encrusting sessile organisms are vital for the establishment of the epibenthic community as both habitat and as a food source (Lukens 1997). 

More importantly, it has been reported that the relative stability of a reef’s community increases with size (Ogden and Ebersole 1981), whereas smaller reefs exhibit a chaotic community structure that lack resilience.  Stochastic processes will continue to influence diversity and abundance, creating a patchwork of differing successional stages.  However, it is this diversity of niches and species that endows larger reefs with their inherent stability.  At sites where sediment infill and abrasion may be problematic, larger artificial reef areas may be required to create an edge effect. 

 

Spacing and Layout

 

Numerous predatory species feed on the infauna of soft bottom habitats that lie adjacent to, or within, natural reef systems. Therefore the layout of the artificial reef should be designed so as to utilise the existing substratum in order to promote system complexity and, as a result, biological diversity.

Appropriate stacking can form additional void space between closely spaced reef units, thereby adding to system complexity.  For solid reef units that individually lack any voids, the formation of pyramid structures creates essential void space with the additional benefit of vertical complexity (White et al.1990).

 

Recruitment of fauna can occur naturally via two pathways; migration from an adjacent habitat and settlement of post-larval juveniles. The degree to which migration contributes to recruitment is dependent upon both the physical isolation of the habitat being observed and the behaviour of individual species (Sale and Dybdahl 1975; Kurz 1995).  Physical isolation is a function of both the actual distance and the amount of protective cover between habitats.  The halo of bare sand that surrounds coral bommies growing in seagrass meadows is a barrier to migration between these two habitats as it is devoid of protective cover, which leaves any migrants exposed to predators.  Vulnerability to predation and encounter rates with predators are major factors that inhibit migration between physically isolated habitats.  Physical isolation can act as a barrier to both juvenile and adult migration to natural or artificial reefs (Doherty 1991; Rooker et al. 1997).

 

An organism’s behaviour may also act as a barrier to migration to isolated habitats.  Many reef organisms are relatively sedentary and rarely leave the confines of the reef after settling as juveniles (Sale and Dybdahl 1975; Ogden and Ebersole 1981).  A number of species are also highly territorial (e.g. triggerfish), so that movement may be restricted to a limited area by inter- and intra-specific relationships (White et al. 1990; Kurz 1995).  There are exceptions to this.  The design of every artificial reef must take into account the life history traits of desired organisms so that migration between individual reef units, between groups of reef units and between the artificial system and adjacent natural systems is not unnecessarily inhibited.  The required level of intra and inter-reef connectivity must be carefully considered.

 

 

The hydrodynamic regime that results from the establishment of an artificial reef can also have a significant effect on the resultant benthic community.  The primary mechanism by which water motion affects physiological processes in corals is the rate of exchange of nutrients (dissolved and particulate), metabolic wastes and gases (i.e. O2 and CO2) across the tissue-water interface.  This in turn influences the rates of photosynthesis, respiration and calcification within the colony (Stambler et al. 1991; Lugo-Fernandez et al. 1994).  Water flow below 10cm.s-1 can inhibit photosynthesis, growth, prey capture and nutrient uptake in hermatypic corals (Sebens and Done 1992).  For example, slow water flow retards dissipation of oxygen from the boundary layer to the water column.  As a result, oxygen builds up in the tissue of the coral, which in turn inhibits photosynthesis (Crossland and Barnes 1977; Jokiel and Coles 1990). 

 

In environments with high, but not damaging water motion, there are a number of benefits for a coral if it can take advantage of the prevailing conditions (Sebens and Done 1992).  Elevated water flow can increase photosynthesis rates by promoting exchange across the tissue-water interface, although respiration rates also increase under these conditions (Dennison and Barnes 1988; Patterson et al. 1991).  Flows above 30cm.s-1 can also inhibit prey capture for many species, predominantly in those corals with large polyps and long tentacles (Sebens and Done 1992).  If the natural hydrodynamic regime is low energy, then the system layout should not significantly reduce this further and may in fact be used to create currents.  Alternatively in a high energy environ, reef units can be placed so as to create patches of low energy habitat thereby increasing system complexity and minimising the effect of sediment abrasion.  Figure 8 illustrates how artificial reefs can affect currents.

Consideration of sediment transport processes is also required when designing the system layout.  Sediment drains or preferential flow paths may be required to prevent sediment infill. 

 

 

Topographical complexity

 

Spacing, layout, void space, volume, profile and surface angle can all influence the overall topographical complexity of an artificial reef system. However if only one type of reef unit is used, the reef system will have an ever repeating and thus non-complex design at the macro scale.  This can be easily overcome by the selective use of different unit designs at different locations within the artificial reef system.

 

For example, to promote patches of benthic encrusting reef, low profile units placed closely together should be used.  At appropriate sites, larger units with a steep profile can be used to attract pelagic species as well as provide greater vertical zonation. Stabilisation of rubble can be achieved at some locations by using Armourflex mats (Clark and Edwards 1994), whilst retention of natural substrata within the system will provide additional variation. The placement of different types of structures provides increased diversity of assemblages within the reef community (Lukens 1997).

 

 

 

: Different reef units (solid blocks, ships and rubble) have been placed to provide topographical complexity (after White et al. 1990).

 

 
Site Evaluation

 

An evaluation of the physical, chemical, biological and socio-economic characteristics of a site during the feasibility stage is essential for the success of any artificial reef project.  Both temporal and spatial variation must be adequately assessed for all attributes listed below.

 

Physical characteristics include:

·         Hydrographic details of area(s);

·         Topographic details of area, including adjacent terrestrial environment;

·         Substrata: particle size, type, depth profile, stability, compaction, areal extent;

·         Water clarity: TSS, sedimentation rates, sediment sources;

·         Irradiance attenuation with depth;

·         Temperature profile;

·         Climate: rainfall, wind speed, wind direction and storm return time; and

·         Hydrodynamic regime: water depth, current speed, current direction, tidal fluctuation, depth related fluctuations, upwelling/downwelling, eddying, wave height and wave periodicity.

 

Chemical characteristics include:

·         pH;

·         Salinity profile;

·         Dissolved Oxygen profile;

·         Biological Oxygen Demand;

·         Background pollutant levels in sediments, water column and biological components; and

·         Sources of potential pollutants. 

 

Biological characteristics include:

·         Abundance, distribution and life history traits of important organisms, e.g. target species, keystone species, system modifiers; 

·         Productivity, biodiversity and species/community dominance of existing system as well as target system (i.e. analogue site);

·         Ecological relationships between existing site and adjacent ecosystems; and

·         Potential recruitment pathways.

 

 

 

 
 
Success Monitoring

 

As with terrestrial restoration projects, inadequate or inappropriate methods to measure success has raised doubts about the perceived benefits of artificial reefs. Unfortunately it is common practice to use a few, very simple indicators of success in order to expedite the process and minimize costs (Gore and Bryant 1988; Cairns 1993).  The most common method of measuring productivity (i.e. success) at artificial reefs has been catch-effort (White et al. 1990).   Catch-effort alone cannot, however, determine whether artificial reefs actually increase total biological productivity through recruitment or whether the structure merely concentrates the pre-existing productivity that already existed through aggregation (Duedall and Champ 1991; Mottet 1985).  Catch-effort also provides no information on ecological processes or functions that would enable a meaningful evaluation of success to be made (Keddy and Drummond 1996). 

 

The monitoring program required will be largely determined by the original project goals.  For example, if one of the goals was to establish a self-sustaining coral reef community with similar biodiversity, resilience and biomass to that of nearby natural reefs, then accepted coral monitoring techniques (e.g. video transects, photo-quadrats, enumeration surveys) would be employed.   If on the other hand, the “health” of corals transplanted to the artificial reef were of concern, then surveys of growth, mortality, disease and symbiont crustaceans would be used to monitor individual transplants.

In general, success monitoring should continue much of the basic physical and chemical site evaluation work listed above.  This will allow an evaluation of the artificial reef system in light of the prevailing environmental conditions. As irradiance, water motion and temperature are three of the most influential abiotic environmental influences on the growth and survival of corals (Sorokin 1995; Veron 1995), these parameters would be automatically included in the monitoring program if corals were a desired component of the artificial reef system.

 

Indicator species or communities that are representative of the desired ecosystem as a whole should also be monitored.  These should include a benthic (e.g. corals and algae), an epibenthic (coral associated fish), a pelagic (e.g. Carangidae) and a cryptic component (e.g. crayfish).  This range of success indicators allows a realistic evaluation of ecological processes and function.  It should be noted that providing the basic physical structure or function of an analogue site is not always sufficient to establish the desired biotic community on an artificial reef.  Certain species or assemblages may also be necessary, as they can play a crucial role in the successful establishment of other biota.  Appropriate monitoring allows ongoing comparisons of the current project status with the desired end-point ecosystem or to a suitable reference (analogue) ecosystem.  This facilitates a feedback management loop that identifies any additional intervention (e.g. modification to reef unit design, introduction of key species via transplantation) that may be required to re-align a restoration project to its desired course as defined in the original goals (Gore and Bryant 1988; Keddy and Drummond 1996).

 

 

 

 

Reef Ball Deployment Location

 

1st Deployment  11 June, 1999

25 57 56N               51 34 36E (Bearing 319 from Control Tower Distance 2.46 Nautical Miles)

 

2nd Deployment 28th September, 2000

25 57 94N               51 34 60 E (Bearing 328 from Control Tower Distance 2.64 Nautical Miles

 

3rd Deployment 28th March, 2001

25 57 86N               51 34 64 E (Bearing 328.1 from Control Tower Distance 2.56 Nautical Miles)

 

Observation by Abdullah Ahmed Jassim Al-Thani

25 57 58N               51 34 28E (Bearing 318.3 from Control Tower Distance 2.52 Nautical Miles)

 

 

 

 

CKECKLIST

 

 

Item No.

Activity

Comments

1.        

Construct Reef Balls

 

2.        

Define Layout( Figure 5 or alternative)

 

3.        

Develop and submit reef ball deployment and management plan

 

4.        

Work permit, Dive permit

 

5.        

Underwater marking (3m from the seabed, underwater float at each corner

 

6.        

Update Reef Map

 

7.        

Subsequent monitoring

 

8.        

 

 

9.        

 

 

10.     

 

 


References

 

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Borntrager, J.F. and Farrell, T.M., 1992.   The effect of artificial reef size on species richness and diversity in a Florida estuary.   Florida Scientist, 55(4); 229-235.   Abstract only, SilverPlatter 3.11 CD-ROM database

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Doherty, P.J., 1991.  Spatial and temporal patterns in recruitment.  In. The Ecology of Fishes on Coral Reefs (Ed P.F. Sale) Academic Press, New York.  pp 261-293.

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Eggleston, D.B., Lipcius, R.N. and Miller, D.L., 1992.  Artificial shelters and survival of juvenile Caribbean spiny lobster Panulirus argus: Spatial, habitat and lobster size effects.   U.S. National Marine Fisheries Service Fishery Bulletin 90(4); 691-702.  Abstract only cited in Silver Platter 3.11 CD-Rom data base.

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Grigg, R.W., 1994.  Effects of sewage discharge, fishing pressure and habitat complexity on coral ecosytems and reef fishes in Hawaii.    Mar. Ecol. Prog. Ser., 103; 25-34.

Guzman, H.M., 1991.  Restoration of coral reefs in Pacific Costa Rica.  Conserv.Biol., 5(2); 189-195.

Hair, C.A. and Bell, J.D., 1992.  Effects of enhancing pontoons on abundance of fish: Initial experiments in estuaries. Bull.Mar. Sci., 51(1); 30-36.

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