New Jersey Scuba Diving

Other important components of the reef community, which were not investigated in this study, but should be recognized as potential future studies to develop a complete picture of the ecology of hard-substrate habitats, include algae (Turner, Ebert and Given 1969), microinvertebrates, ichthyoplankton (Stephens and Pondella 2000) and microorganisms (Turner, Ebert and Given 1969).

Factors Influencing the Study

While 15 experimental habitats had an average of 47.6 times more surface area than the footprint of sandy sea floor they covered, they only had 4.5 times more surface area than a solid block of the same dimensions. Even so, the experimental habitats probably have greater surface area per volume than most reef construction materials. Wire comprised 18 percent of the habitats' surface area. Wire was not well colonized and therefore, provided little value as colonization substrate for epibenthos. With greater surface area available for biological colonization, it is reasonable to assume that the experimental habitats had greater levels of biological colonization than equal volumes of other reef structures. It is also reasonable to conclude that the experimental units did not represent the optimum habitat for most, if not all, species and thus, it is probable that even more productive habitats could be designed by increasing surface area and providing even more suitable living spaces. One certain way to increase biomass per footprint would be to build a habitat with a greater profile.

The colonization plates represent a more direct relationship between the surface area provided by the experimental habitats and that of actual reef substrates of the same material. One difference between the experimental plates and in situ reef substrates is that the colonization plates were all vertically oriented. Wendt et al. (1989) found that epibenthic colonization was significantly greater on vertical than horizontal surfaces. In a Delaware Bay study, the underside of horizontal reef structures (ceiling) was most productive (Steimle et al. 2002).

The proximity of the experimental habitats to the sea floor and their relatively low profile (77 cm) may also have influenced the survival of many marine colonizers, some positively, some negatively. Animals that live in, on or near the sea floor, like crabs, urchins, starfish and tube worms, probably benefited from a low-profile habitat. Attached organisms, such as blue mussels, barnacles and anemones, may have been negatively influenced by colonizing near the bottom, since there, they are more susceptible to predation, sand scouring and siltation. General observations by divers suggest that mussel colonies are denser and comprised of larger individuals on the upper portions of shipwrecks.

The effects of physical and chemical parameters, such as storms, temperature and hypoxia, on the marine life assemblages colonizing the units were not examined, but are recognized as possibly influencing year-to-year fluctuations in marine life diversity and abundance.

The units were retrieved in October in an attempt to maximize the presence of YOY fish recruited before they migrated in response to declining water temperature. It is expected that our findings on fish and other marine life would have been different if the season of retrieval was varied.

Since many taxa were not identified to the species level, the total number of species inhabiting the experimental habitats probably exceeds the 145 reported taxa. The improved ability to identify species and better preservation of samples following the first-year sampling may have led to greater numbers of taxa and species being identified in latter samples.

Abundance

Sessile Epibenthos

On steel (shipwrecks), two-dimensional substrates in a different zoogeographical region off South Carolina and Georgia, Wendt et al. (1989) found that scrape samples had a standing stock biomass of sessile epibenthos of 2,486 to 3,916 g/m² on horizontal surfaces and 4,218 to 7,726 g/m² on vertical surfaces. On New Jersey reefs, Figley (1989) observed an average sessile biomass of 1,383 g/m² on the exposed outside of concrete-ballasted tire units (rubber substrate) and 3,381 g/m² on the protected interior. On a marine reef located at the mouth of Delaware Bay, Steimle et al. (2002) compared the annual production of epifauna on a concrete reef structure with that of the infauna of the surrounding sandy bottom over the 5-year period 1989-1994. On an equal footprint basis, the production of natural bottom infauna was 217-251 kcal/m²/yr as compared to 3,994-9,281 kcal/m²/yr of epifauna on the reef substrate. The current study found an average of 623 g/m² of sessile epifauna on external colonization plates and 1,133 g/m² on internal ones. These values are below those of the previous studies ( Wendt et al. 1989, Figley 1989 and Steimle et al. 2002. )

No studies in temperate waters were found that also included mobile invertebrates and small fish in their investigations of biomass of reef communities. In our study, the inclusion of these other organisms and the additional attachment surfaces for sessile epifauna provided by the entire three-dimensional experimental habitat produced a high biomass/footprint ratio. The mean biomass of all organisms on 15 habitats over the 96-month study period was 84,175 g/m² of sea floor footprint. Off New Jersey, blue mussel dominates reef epifauna, accounting for 63 percent of the overall biomass throughout the current study. Similarly, Steimle et al. (2002) found that the substantial annual variability in reef epifaunal biomass was attributable to the recruitment success of mussels.

Small Fish

Over a 14-year study, Pondella and Stephens (1999) found that the density of cryptic fishes varied from 0.016 to 0.640 individuals per m² on a California reef. Adams (1993) observed large numbers of YOY (<3 cm) black sea bass, scup ( Stenotomus chrysops), cunner and other species using an artificial reef off Virginia. During a 5-month study in which plastic boxes filled with clam shells were used to mimic reef structure on a New Jersey reef site, Figley (1994) found mean densities of 47 YOY and 8 post-YOY fish/m² of 8 species living within the artificial habitats. The density of small fish trapped within the experimental habitats of our investigation far exceeds those of the other studies. Over the 8-year study, an average of 105.7 small fish were found per m² of experimental reef habitat. These findings indicate that complex reef habitat that offers crevices and small enclosed spaces provides excellent habitat for small fish.

Small fish represented only 1.2 percent of the average total biomass of all taxa on the experimental habitats. Therefore, the ratio of forage base to small fish biomass was 82:1. This ratio suggests that a complex habitat also provides an extensive forage base for small fish. Adding an estimate of adult fish from another New Jersey study (Figley and Daetsch 2004) suggests that total (large + small) fish biomass may have represented 4.5 percent of total reef biomass. Then, the total fish-to-forage ratio on the reef habitats would then be about 21:1.

Lobster

Our study also demonstrated the importance of cryptic habitat as escape cover for juvenile lobster. Over the 96-month study, a mean of 14.9 young lobster (rostrum to telson length: 24-145 mm) were observed per m² of experimental habitat footprint. Large lobsters were excluded from the experimental habitats by the mesh box. It should be noted that no lobsters were found in the habitats during the 2003 and 2004 collections; it is possible that the absence of young lobster was due to a general and extensive mortality of lobsters in the New York Bight during that period. With an extensive sandy sea floor, it is reasonable to assume that the scarcity of cryptic habitat for the survival of young lobster is a limiting factor to recruitment of adult lobster in New Jersey. The potential for man-made reefs to increase survival and recruitment of lobster may be substantial, although the characteristics of the reef structure must fit the habitat requirements of both post-larval and juvenile lobster.

Colonization Substrates

The rate and extent of colonization by sessile epibenthos is influenced by the type of fouling substrate. Smooth or slippery surfaces, such as glass, may make attachment difficult and therefore, decrease the fouling rate. The presence of toxins, such as active lime in fresh concrete, zinc on metal surfaces or anti-fouling ingredients in paint, also reduces fouling. In general, rough substrates are considered best for bio-fouling.

In California, Turner, Ebert and Given (1969) used wooden blocks to monitor fouling, but saw the wooden substrate disintegrate rapidly due to wood-boring crustaceans. In an experiment evaluating a variety of reef substrates, Chang and Pearce (1995) ranked their study materials in terms of biological colonization rates in the following order:

Rubber > Concrete > Steel > Wood > Aluminum

During the current study, we examined four common reef-building materials and found the following rank based on mean total biomass:

Rock > Concrete > Rubber > Steel

However, the fouling rate depended upon the location of the plates either inside or outside the mesh, as follows:

Inside Mesh

Rock > Rubber > Concrete > Steel

Outside Mesh

Concrete > Steel > Rock > Rubber

However, the differences in mean biomass of the four materials were not statistically significant, suggesting that all four reef-building materials used in New Jersey's Reef Program are relatively equal in production of fouling growth. Thus, it is reasonable to conclude that all of the reef-building structures used in New Jersey - rock, concrete pieces, tires (not used anymore), Reef Balls (concrete), shipwrecks, army tanks, steel-armored cable and subway cars - provide substrate of similar value to the fouling community and would be expected to produce similar biomasses of encrusting marine life per unit of substrate surface area.

Unlike the other three materials, steel has the unique property of corroding and flaking. The sloughing of the surface layer precipitates an accompanying loss of encrusted growth and the presentation of a clear surface open to subsequent colonization (Steimle, personal communication).

Predation

The grazing of reefs by both vertebrate and invertebrate predators can greatly reduce the biomass of the fouling community. Falace and Bressen (1999) found significant grazing of macrophyta by sea urchins on a reef in the Ligurian Sea. Off New Jersey, dense mats of blue mussel spat that appear in spring are often grazed clean by fish, crustaceans and starfish before winter. Over the current 96-month study, the mean biomass on colonization plates exposed to predation on the outside of the experimental habitats was 80 percent less than plates inside the mesh. Since there were also predators, such as crabs, lobsters, starfish and sea urchins, on the inside of the unit that undoubtedly grazed on the protected fouling growth, the actual level of predation on the unprotected plates was probably considerably higher than that observed. Standing stock biomass is only a static measurement of the (secondary) productivity of a reef. It is not an indication of all the biomass that was produced over the extended time periods both before and after samples were collected.

Succession

It is generally noted that fast-growing, short-lived species are usually the first fouling organisms to colonize temperate reefs, followed by slow-growing, long-lived species that eventually replace the initial colonizers. Off New Jersey, hydroids, bryozoans, barnacles and blue mussels are the first visible organisms to appear on reef substrates, followed by anemones, stony coral and sponges. However, succession is often interrupted by dynamic events, like storms, which scour life from lower reef surfaces and allow for fresh colonization and a repeat of successional events.

In a California study at a similar depth to the current study, Turner, Ebert and Given (1969) identified the following successional stages on reef structures over a 5-year period:

1. algae - bacteria
2. barnacle - hydroid
3. mollusk - polychaete
4. ascidian - sponge
5. ectoproct
6. anemone - stony coral

Wendt, Knoll and Van Dolah (1989) found no difference in species diversity, abundance and percent coverage of epibenthos on shipwrecks of ages between 3 and 10 years off South Carolina and Georgia. They reported no sponge or hard coral growth on wrecks as old as 10 years. During a 25-month study of colonization plates located off the New Jersey coast, Chang and Pearce (1995) reported successional changes in epibenthos assemblages. They noted that the presence of some species excluded the subsequent appearance of others. In a study of epibenthic colonization of tire rubber surfaces on New Jersey reefs, Figley (1989) found that the initial colonizers (123 days) were hydroids and bryozoans, followed by mussels and barnacles on older-aged surfaces (up to 823 days). Early colonizers and possibly initial succession may be influenced by the coincidence of reef deployment and spawning activities of fouling species.

In the current study, ectoprocts, mussels and barnacles quickly colonized the experimental habitats. Slower growing taxa, such as stony coral and cnidaria, increased in abundance over time. Oddly, sponge showed a gradual rise in abundance and then a decline during the 96-month sampling period. Sponge had a very low biomass in all sample periods and may take a much longer time period before it attains a significant level of abundance. It is believed that the rise in annelida and nemata abundance over time was primarily a function of the units sinking into the sandy bottom and/or accumulating silt in unit spaces, providing the soft sedimentation in which these taxa thrive.

Enhancement Value

The following comparison of standing stock biomass of benthic fauna from the sandy sea floor in 10 to 20 m depths off central New Jersey with that of experimental reef habitats was prepared in most part by Frank Steimle, James Howard Marine Lab, National Marine Fisheries Service (Table 8).

Table 8

A summary of reported standing stock biomass (g/m² wet weight) values (rounded) for the benthic infauna and epifauna on sand sediments of the New York Bight and the enhancement ratio of the mussel-dominated biomass of the experimental reef habitats (our study) over that of the sandy sea floor.

* = original AFDW values converted back to wet weight using taxa specific conversions based on Steimle and Terranova (1985); these ranged from 15.3 for bivalve mollusks to 3.8 for benthic crustaceans and minor taxa.

A review of databases suggests that the sandy benthic infauna and sessile epifauna of the area near our reef study site have two common community abundance states. One state is when the benthic sand community is colonized and dominated by populations of either or both the surf clam or the sand dollar (Echinarachnium parma) and species commonly associated with these two species, such as predatory moon snails (Euspira heros) and sea stars (Asterias sp.). The other state is when the benthic community is dominated by a mixture of polychaetes, small crustaceans, such as amphipods, smaller, less-domineering mollusks and other macrofauna.

When there has been a successful recruitment and sustained population of surf clams or sand dollars, the wet weight biomass of the area can be about or greatly exceed 500 g/m² (Table 7). When either of these two species are not colonizing an area, the wet weight benthic community biomass is commonly an order of magnitude less, or about 30-50 g/m².

The enhancement ratios of standing stock biomass of the mussel-dominated experimental reef habitats (mean of all samples over an 8-year period = 83,175.8 g/m² excluding fish biomass) vs. sand sediment infauna range from 35 to 1,124 times for surf clam-dominated sand substrate and 2,773 to 3,200 for polychaete/crustacean-dominated sediments. The highest single-year mean biomass for the experimental habitats was 152,249.6 g/m² reached during the 2003 collection. This level of community biomass was probably near the carrying capacity for this habitat design. The 2003 reef habitat biomass exceeded the surf clam-dominated sand by a range of 64 to 2,057 times and the polychaete/crustacean-dominated substrate by a range of 5,075 to 5,859 times. Steimle et al. (2002) found that a concrete reef located at the mouth of Delaware Bay exhibited an enhancement ratio of 168 to 354 times the infaunal biomass from an equivalent area of the surrounding sandy sediments. Tinsman and Hense (personal communication, Delaware Division of Fish and Wildlife) compared reef epifauna with natural bottom infauna in a variety of salinities in Delaware Bay and the Atlantic Ocean. They found that epifauna communities had 6 to 400 times greater biomass than nearby infauna communities.

The dual community state on New Jersey coastal sandy sediments is similar to the dichotomous situation on hard surfaces in the same area. In one reef state, the biomass of the epibenthic community is largely determined by the presence and abundance of blue mussels. The other reef state, which may be an ultimate successional stage, is dominated by cnidarians, such as anemones, coral and hydroids (Steimle et al. 2002). These animals may inhibit the colonization of mussels by occupying reef substrates and feeding on mussel spat. Their dominance may be prolonged due to reproduction through budding rather than larval recruitment. Dramatic events, such as storms, may be necessary to displace cnidarian communities and open reef substrates to colonization by mussels and other encrusting epibenthos. While mussels dominated the experimental reef habitats over the 96-month study, cnidarian populations increased continuously. Cnidarians are of lesser value as food for most marine life, and this state represents a much less productive reef community in terms of providing forage for fish and lobster. Therefore, the enhancement ratio of a cnidarian-dominated reef would be much lower than that of a mussel-dominated reef structure.

The high biomass of surf clam-dominated sand bottom illustrates the importance of the open sand in providing a food resource for reef inhabitants. For this reason, reefs should be constructed apart from each other, separated by extensive expanses of sandy bottom. Since commercial dredges are not used on reef sites, surf clam resources located within reef boundaries are not subject to harvest and are thus fully available as forage for reef denizens.

Are We Meeting Reef Program Objectives?

The biological objectives of New Jersey's Reef Program are listed in the Draft Reef Management Plan for New Jersey (Figley 2003) as follows:

1. create hard-substrate, reef habitat for marine fish, crustaceans, shellfish and encrusting organisms;
   
2. provide spawning, nursery, refuge and feeding areas for marine life;
   
3. increase diversity and abundance of marine life.

The results of this study demonstrate that the Reef Program's biological objectives are being achieved. Without reiterating preceding discussions, the achievement of reef objectives can be briefly illustrated by the following survey findings:

1. reef structures provide habitat for 145 taxa of fish and marine life
   
2. reef structures provide habitat for hundreds to thousands of times more biomass of marine life than similar areas of the sandy sea floor
   
3. sessile and sedentary marine life comprise 87 percent of reef community biomass; these animals need reef structures to live and reproduce
   
4. experimental reef habitats supported an average of 105 YOY and small fish and 14 juvenile lobsters per m² of habitat footprint
   
5. unprotected reef surfaces had 80 percent less encrusting marine life, suggesting a high level of predation upon reef organisms and demonstrating that reef epifauna represent a large food resource in the marine food web.

Application of Results

The results of this study provide relevant applications for designing both reef structures and reef sites. The reef materials currently used by the Reef Program to build reefs - rock, concrete and steel - all provide suitable substrate for the colonization of sessile, encrusting marine life. Reefs can be more productive by designing structures with greater surface area. Greater surface area per sea floor footprint can be achieved by increasing structure profile, by using hollow structures and by having irregular, rather than flat, surfaces.

Reef structures should also be complex, with a variety of openings, crevices and chambers. Complexity provides the protective habitat needed by mobile invertebrates and YOY fish. Most reef structures, such as vessels, concrete pieces and Reef Balls, do not optimize surface area or complexity. Off New Jersey, rock piles may represent the most complex reef structure because of their irregular substrate and numerous small openings. There are currently no commercially available reef structures that maximize surface area and complexity. Many commercial reef structures, especially those from Japan, maximize space (volume) and minimize structure (mass). This approach provides the greatest volume of reef structure for the least cost. The result is large, open structures that are used extensively by large numbers of adult fish. If fish harvesting is the ultimate goal, this design is preferred.

From an ecological perspective, however, this approach in reef design may be illusory. An ecologically healthier tactic is to create a habitat dominated by taxa from the lower levels of the food chain. The higher the forage base to fish biomass ratio, the closer the reef community will resemble a natural marine food chain. By using reef structures that do not concentrate large numbers of adult fish in small areas, fishing mortality can also be reduced. Furthermore, complex reef habitats may increase survival of YOY fish and lobster, which eventually will recruit to and benefit fisheries. Unfortunately, the fabrication and deployment of significant quantities of specially designed, complex habitats is economically prohibitive at this time.

The results of the experimental reef habitat colonization study also suggest that variety in habitat is an important factor influencing biological diversity. The more diverse a reef site is in terms of types, sizes, heights, shapes and complexities of the various reef structures of which it is comprised, the more diverse the biological community colonizing the site. Thus, many types of reef structures should be dispersed on each reef site. Both the sandy bottom and open water column are also important components of the reef site. Reef sites should be designed to maximize the edge and interspersion of reef structures with these other two environs.

CONCLUSIONS

1. During the 96-month study, a total of 145 taxa were identified living within the experimental reef habitats.
   
2. Over the course of the 96-month survey, experimental reef habitats were colonized by an average of 534,566 individual marine life organisms and had a total mean biomass of individual and colonial organisms of 84,175g /m² of sampling unit footprint. Colonial organisms covered 87,554 cm² of surface area/m² of habitat footprint.
   
3. The experimental reef habitats were more complex and had greater surface area than most actual reef structures and, consequently, probably also had a greater density of marine life than would be expected on currently used reef structures of the same profile.
   
4. The biomass/footprint ratio of the experimental reef habitats could be increased by optimizing hiding spaces and by increasing both surface area and profile.
   
5. There were considerable year-to-year fluctuations in sampling unit total biomass, with the dominant species, blue mussel, largely responsible for such variations.
   
6. The experimental habitats provided refuge cover for large numbers of small and YOY fish (105.7/m²), crab (4,639/m²) and lobster (14.9/m²).
   
7. In terms of mean total standing stock biomass, colonization substrates were ranked as follows:
   
   rock > concrete > rubber > steel
   
8. However, since the differences in the colonization rates of the 4 substrates were not statistically significant, the statistical relationship between substrates is actually:
   
   rock = concrete = rubber = steel
   
9. Colonization plates inside a protective mesh cage had a significantly higher biomass than those outside the mesh, suggesting that predation reduced standing stock biomass by at least 80 percent.
   
10. In terms of biomass, the forage base to small fish ratio of the experimental habitats was 82:1.
    
11. Over the course of the study, on an equivalent area basis, the biomass enhancement ratios of the experimental reef habitats over surf clam-dominated and polychaete/crustacean-dominated sand bottom ranged from 35 to 180 and from 1,126 to 3,205 times, respectively.
    
12. Based on the amount of space remaining in the habitats and the greatest sampling year mean biomass, the carrying capacity of the experimental habitats (l m x l m x 77 cm) was about 152,801 g.
    
13. Attention should be focused on designing and deploying complex reef habitats that benefit lower-level consumers and provide refuge cover for both YOY fish and juvenile lobster.

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