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Artificial Reef Study 2004

Marine life colonization of experimental reef habitat in temperate ocean waters off New Jersey, 1996-2004
Marine life colonization of experimental reef habitat in temperate ocean waters off New Jersey, 1996-2004

By Jennifer Resciniti and Bill Figley
November 2005

This investigation was partially funded by the
Federal Aid to Sportfish Restoration Program



TABLE OF CONTENTS

ABSTRACT

ACKNOWLEDGMENTS

INTRODUCTION

METHODS

  • The Experimental Habitat
  • Study Site
  • Deployment
  • Retrieval
  • Lab Analysis
  • Statistical Analysis

RESULTS

  • Nomenclature
  • Sample Size
  • Species Diversity
  • Abundance and Biomass
  • Colonization Plates
  • Predation
  • Observations

DISCUSSION

  • Factors Influencing the Study
  • Abundance
  • Sessile Epibenthos
  • Small Fish
  • Lobster
  • Colonization Substrates
  • Predation
  • Succession
  • Enhancement Value
  • Are We Meeting Reef
    Program Objectives?
  • Application of Results

CONCLUSIONS


LIST OF TABLES

LIST OF FIGURES

REFERENCES CITED



ABSTRACT

A biological colonization study of experimental reef habitats in temperate ocean waters off New Jersey was conducted over a 96-month period. A total of 145 different taxa of 9 phyla were identified within the experimental units, including 42 arthropoda, 37 annelida and 43 molluska. Individual organisms had an estimated mean abundance of 534,566 organisms/m2 of habitat footprint, including 105 fish, 4,639 crabs and 14 lobsters. Colonial organisms covered 87,554 cm2 of the habitat surface area. Mean total biomass of the organisms inhabiting the units was 84,175 g/m2, with blue mussel comprising 63 percent of the total. The carrying capacity of the experimental habitat for all species of marine life was about 152,801 g/m2. Predation accounted for an 80 percent reduction of biomass between surfaces exposed and not exposed to predators. There were no statistically significant differences in biological colonization rates of sessile epibenthos on concrete, rock, steel and rubber substrates. On an equivalent area basis, the biomass enhancement ratios of the experimental reef habitats over surf clam-dominated and polychaete/crustacean-dominated sand bottom habitats ranged from 35 to 1,124 and 2,773 to 3,200 times, respectively. A simplified, three-tiered reef habitat food chain consisted of 84.5 percent sessile/sedentary invertebrates, 11.0 percent mobile invertebrates and 4.5 percent juvenile and adult fish. The results suggest that complex reef habitats provide both attachment surfaces and refuge habitats that support a diverse and abundant marine life community.



ACKNOWLEDGMENTS

The Ocean County Bridge Department transported the experimental habitats to the Barnegat Light Reef Site. The U.S. Environmental Protection Agency dive team retrieved a habitat during the first year of the study. Roger Hoden and George Dreher retrieved habitats in subsequent years. Linda Barry assisted in field collection and performed laboratory and data analysis. Frank Steimle, National Marine Fisheries Service, assisted in field collections and identifications and reviewed the manuscript. Jeff Carlson, Barry Preim and Stacey Reap assisted in habitat fabrication, habitat retrieval or laboratory analysis. Statistical analyses were performed by Deborah Vareha. Barry Preim prepared the graphics. Mary Anne Lyons and Tricia Mahoney typed the manuscript. This investigation was partially funded by the Federal Aid to Sportfish Restoration Program.



INTRODUCTION

An inventory of the biological attributes of marine life communities inhabiting reefs, including species diversity, biomass, life stages, predation level, habitat preferences and succession, is an essential ingredient of any reef-building program. Biological monitoring is especially important in assessing the effectiveness of New Jersey's reef program in meeting its primary objective of providing habitat for fish and invertebrates (NMFS 1995).

While most artificial reefs are built for economically important fish, food and game shellfish (lobsters, oysters) and/or fishermen and divers, the epifaunal invertebrate community is an important ecological component of the reef community, providing the basis of the food chain that supports harvestable resources and comprising the vast majority of life, by numbers and biomass, inhabiting ocean reefs. The intention of this investigation was to inventory the smaller, mobile and sessile invertebrate communities and juvenile fish inhabiting New Jersey reefs. No attempt was made to examine adult fish populations.

Turf or fouling communities, composed of sessile, invertebrate epifauna and algae, in shallower waters, are inventoried in a variety of ways. Palmer-Zwahlen and Aseline (1994) used divers to identify fouling organisms found within randomly selected quadrants. Feigenbaum et al. (1985) and Foster et al. (1994) had divers scrape reef surfaces and collect samples for laboratory analysis. Wendt et al. (1989) combined scrape samples with underwater photographs to inventory turf communities. Many researchers have placed settlement plates of various reef-building materials on sea floor racks that can later be retrieved by divers for laboratory analysis (Sheehy 1983; Woodhead and Jacobson 1985; Bailey-Brock 1989; Hawkins 1995; Tumbiolo et al. 1995; Chang and Pearce 1995).

The collection of cryptic or mobile epifauna, which includes crabs, shrimps, worms, snails, starfish and small juvenile fish, is more challenging since these animals are small, cryptic and often hide in holes and crevices in reef structures or among sessile epifaunal growth. Benson (1989) used a suction device to capture mobile prey in turf scrape samples. Traps and nylon bags are also used to capture certain mobile invertebrates (Forrest Blau and Byersdorfer 1994). The shortcoming of using traps is that they do not provide information regarding the numbers of mobile invertebrates per unit of habitat. In clear, tropical waters, the common method of evaluating juvenile fish populations is through counts by divers (Gorham and Alevizon 1989; Danner et al. 1994; Jessee et al. 1985; Adams 1993; Bohnsack et al. 1997; Brock and Kam 1991).

The use of divers to observe mobile epifauna and juvenile fish and to quantify their population size underwater on New Jersey reefs is impractical because of poor visibility, and the cryptic habits or large population numbers of many of the species. Another factor that prohibits using diver observations to collect biological information is the vast amount of field time that is needed to accomplish the task. For these reasons, we decided to use specially designed, miniature reef habitats as experimental sampling units that could be placed on the sea floor and later retrieved by divers, disassembled, and samples returned to the lab for analysis. The experimental habitats were designed to afford extensive colonization surfaces for sessile epifauna, including 8 settlement plates of 4 common reef-building substrates, numerous and varied hiding spaces for mobile epifauna and an internal chamber for juvenile fish. Thus, all of the components of the reef community that we were investigating could be collected simultaneously in a few hours and brought back to the lab where a thorough, detailed analysis could be completed.

According to Seaman (2000), our study was designed to obtain first-level information about temperate reef biology - species diversity, abundance, biomass, size ranges and predation pressure. Specifically, the objectives of this reef performance monitoring survey included:

  1. an inventory of the sessile and mobile epifauna and juvenile fish inhabiting an experimental reef habitat;

  2. a quantification of the standing stock biomass of sessile and mobile invertebrate epifauna and juvenile fish per unit of habitat volume on an experimental reef habitat;

  3. an examination of the successional changes in species diversity and standing stock biomass of epifaunal invertebrates on an experimental reef habitat over time;

  4. a comparison of the colonization rates of sessile invertebrate epifauna on 4 different reef-building substrates;

  5. an investigation of predation pressure on sessile invertebrate epifauna on 4 different reef-building substrates.



METHODS

The Experimental Reef Habitat Sampling Unit

The design parameters that guided the development of the experimental reef habitat sampling unit included:

  1. heavy base for undersea stability;
  2. height and width dimensions small enough to fit inside a plastic drum;
  3. vertical orientation to provide enough height off the bottom to obtain a true reef, rather than sand, sample;
  4. inside and outside attachment surfaces for 8 colonization plates;
  5. a variety of small cavities and cryptic spaces; and
  6. a screen enclosure to exclude large, predatory fish.

Experimental reef habitat
Figure 1. Experimental reef habitat

An experimental reef habitat ready for deployment
Figure 2. An experimental reef habitat ready for deployment

It should be noted that the experimental reef habitat was a sampling unit and did not represent any structure currently used to build reefs. Henceforth, they will be referred to as experimental reef habitats, sampling units or, simply, units. The structural components of the experimental habitat consisted of a rectangular closed box (height: 77 cm, width: 32 cm x 32 cm) constructed out of 12.5-gauge plastic-coated wire of 2.5-cm-square mesh imbedded vertically into a base made from a truck tire filled with concrete (Figures 1 and 2). The base was used only for ballast and weighed 200 to 250 kg. Vertical plastic pipes were added to ensure rigidity of the box, and a reinforcing rod was installed as a lifting eye.

Ten corrugated plastic roofing panels were placed inside the wire mesh box. Each layer was rotated 902 to produce a honeycomb effect. Approximately 50 whelk (Busycon sp.) shells were placed on top of the panels to provide a complex maze of hiding spaces, cavities and attachment surfaces.

The upper portion of the box consisted of a hollow chamber completely enclosed by the wire mesh. Two plates each of four different materials - rubber, concrete, steel and rock - were attached back to back to the upper chamber of the box, with one plate outside and one plate inside the mesh (Figure 3). The plates represented four common reef-building materials and served as colonization substrates for sessile epifauna. The plates on the outside of the wire cage were open to predation from large fish and invertebrates; those inside the cage were protected from large predators, although some crabs that established themselves as juveniles within the unit did grow to adult size and were trapped within the cage.

Top view of experimental reef habitat unit
Figure 3. Top view of experimental reef habitat unit

Location of reef structures around experimental reef habitats
Figure 4. Location of reef structures around experimental reef habitats

The experimental habitats have a mean height of 77.3 cm, a sea floor footprint of 1,034 cm2 and encompass a volume of 79,609 cm2 (Table 1). The wire cage itself has a mean surface area of 8,626 cm2, although this attachment surface consists of small diameter (0.3cm) wire. The fiberglass panels (top and bottom) have a combined surface area of 14,855 cm2. The whelk shells (inside and outside shell surfaces) have an approximate total surface area of 22,730 cm2. For the colonization plates, only the exposed flat surface and edge were measured, the back-to-back surfaces were not counted.

The colonization plates have the following mean surface areas: concrete = 1,053 cm2; steel = 776 cm2; tire = 572 cm2; rock = 574 cm2. The mean total area of attachment surfaces for the entire habitat is 49,186 cm2. Therefore, each experimental reef habitat provides an increase in surface area of 47.6 times that represented by the sea floor footprint of the habitat. In comparison, a solid block the same height as the experimental habitat would have a surface area to footprint ratio of 10.6. Thus, the experimental habitat provided a complex, cryptic habitat with extensive surface area available to biological colonization.


Table 1

Mean dimensions of 10 experimental reef habitats, 1998-2001.

Parameter Unit Mean SD
Sea Floor Footprint cm2 1,034 64
Habitat Volume cm2 79,609 6,608
Wire Cage Area cm2 8,626 430
Fiberglass Panel Area cm2 14,855 1,566
Whelk Shell Area cm2 22,730 3,130
Concrete Plate Area cm2 1,053 93
Steel Plate Area cm2 776 26
Tire Plate Area cm2 572 42
Rock Plate Area cm2 574 70
Total Habitat Area cm2 49,186 4,217

Study Site

The study site was the Barnegat Light Reef Site. This site is located in the northwestern Atlantic Ocean, 3 nm offshore of Barnegat Light, NJ. The depth is 17m. The sea floor consists of coarse sand, gravel and pebbles. Reef structures placed on the site include concrete-ballasted tire units, Reef Ball concrete habitats, hollow concrete castings, obsolete army tanks and 3 small steel vessels (Figure 4). As of 2004, the total volume of reef structure on this site is 7,532 m2; the total footprint of reef structure is 7,375 m2.


Deployment

In October 1996, 30 experimental reef habitat sampling units were placed on the study site from a motorized barge operated by the Ocean County Bridge Department (Figure 5). After the barge was anchored, the experimental habitats were individually lowered to the sea floor using a tether line and submersible float equipped with a release hook. This was done to ensure that the units landed upright. The units were spaced apart in a group about 30 m in diameter (Figure 6).

Thirty experimental habitats en route to the Barnegat Light Reef study site
Figure 5. Thirty experimental habitats en route to the Barnegat Light Reef study site

Divers sent the encapsulated habitats to the surface using an air lift bag
Figure 6. Divers sent the encapsulated habitats to the surface using an air lift bag


Retrieval

In October of each year, experimental habitats were retrieved by divers. Each of these units was quickly enclosed within a plastic drum which sealed against the tire base (Figure 7) to trap the organisms inside. Once enclosed, each unit was raised to the surface using an inflatable lift bag. The unit was then lifted into the boat using an electric winch and davit and placed inside a plastic tub (Figures 8 and 9). After removing the drum, the wire mesh was cut open with wire cutters (Figures 10-12). The following items were removed and inserted into resealable, 10-liter plastic bags: 8 colonization plates, 2 fiberglass panels, 5 whelk shells (Figure 13), and a sample of wire mesh.

The sample panels and whelk shells were randomly selected. The remaining sand, gravel, shell hash and other debris were scraped off what remained of the box and deposited into the tub. During unit breakdown, large organisms (>3 cm), such as crabs, lobsters and fish were removed and placed in plastic, 5-liter jars filled with 10 percent formalin solution. The contents of the tub were rinsed through a 0.5-mm mesh sieve and bagged as bulk samples. All samples, with the exception of the samples in formalin, were stored on ice in coolers for transport back to the lab, where they were frozen.

Divers encapsulated the experimental reef habitat units inside<br>
a plastic drum, trapping most marine life inside
Figure 7. Divers encapsulated the experimental reef habitat units inside
a plastic drum, trapping most marine life inside

Retrieving an experimental reef habitat<br>
unit encapsulated in a plastic drum
Figure 8. Retrieving an experimental reef habitat
unit encapsulated in a plastic drum

The experimental habitat units were placed in<br>
a plastic collection pool before being dismantled
Figure 9. The experimental habitat units were placed in
a plastic collection pool before being dismantled

The wire mesh cage is cut open to access experimental substrates
Figure 10. The wire mesh cage is cut open to access experimental substrates

The opened habitat unit showing<br>
whelk shells and corrugated panels
Figure 11. The opened habitat unit showing
whelk shells and corrugated panels

The opened habitat showing upper chamber
Figure 12. The opened habitat showing upper chamber

Marine life growth on whelk shell
Figure 13. Marine life growth on whelk shell


Lab Analysis

Various techniques were employed to examine and remove organisms from the different components of the unit. Whelk shells were measured for length, then cut in half with a miter saw equipped with a 2 mm-wide masonry blade to expose the inside of the shell. The shells and the fiberglass panels were analyzed in a similar fashion. All mobile invertebrates and sessile, individual organisms, such as anemones and mussels, were removed, sorted by species, counted, weighed in aggregate, and measured. In 1998 and 1999, weights were measured to the nearest 0.1g on a triple beam balance. From 2000 on, weights were measured to the nearest 0.001g on an electronic balance. All weights were reported as damp weights that included shell. Live barnacles and tubeworms were counted, and when possible, removed and weighed. The surface areas covered by colonial, encrusting bryozoan, hydroid, stone coral and sponge colonies were estimated using sheets of clear plastic printed with a 1-cm-square grid. Due to their fragility, most hydroid colonies did not withstand the freezing and thawing process well enough to do more than obtain weights. The percent area of coverage of the wire mesh by encrusting colonies was estimated visually in increments of 25 percent for each 2.5 cm wire segment.

All of the preceding types of samples were then individually rinsed into a 0.5mm mesh sieve along with residual contents left inside each sample's collection bag. The contents of the sieve were then placed under a dissecting microscope to sort, identify, count, and measure the additional mobile invertebrates for each sample.

Colonization plates were sorted individually (Figures 14-16). First, all large mobile organisms were removed for later analysis. Second, the percent coverage of plate surface area by colonial species was estimated using the 1-cm-square grid. Third, attached sessile, individual organisms, such as anemones, tubeworms, barnacles, slipper shells ( Crepidula spp.), mussels ( Mytilus edulis), and jingle shells ( Anomia sp.), were counted. These organisms (when possible to remove in their entirety) were then weighed. Only the organisms found on the exposed surfaces of the plates, i.e. tops and sides, were collected for analysis. Each plate and the contents of the bag containing it were then rinsed into a 0.5-mm sieve to retrieve any remaining mobile organisms for later analysis.

Marine life growth on concrete colonization plates located outside mesh (top) and inside mesh
Figure 14. Marine life growth on concrete colonization plates located outside mesh (top) and inside mesh

Marine life growth on rock colonization plates located outside mesh (top) and inside mesh
Figure 15. Marine life growth on rock colonization plates located outside mesh (top) and inside mesh

Marine life growth on rubber colonization plates located outside mesh (top) and inside mesh
Figure 16. Marine life growth on rubber colonization plates located outside mesh (top) and inside mesh

The samples of the large animals extracted and placed in formalin and the mobile invertebrates taken from the colonization plates were independently speciated, counted, weighed and measured. Since these bulk samples proved to be too large to sort and quantify in their entirety, the following procedure was used to obtain random subsamples of at least 10 percent by weight for each unit: First, the sample was weighed; second, the sample was thoroughly mixed and spread to an even depth on a tray; third, a spatula was used to scoop subsamples from randomly chosen locations on the tray; fourth, the subsample was weighed, speciated and enumerated following the same procedures used for the preceding samples.

Samples of certain attached or encrusting taxa, such as barnacles, bryozoans, hydroids, stone corals ( Astrangia astrelformis) and sponges, were removed and weighed to determine a per unit weight, by number for barnacles, and by area for the colonial encrusting organisms. The total weights of these taxa were estimated, by expanding per unit weights to the total number for barnacles and the total surface area for colonial invertebrates.

Length frequencies by species were obtained by measuring individuals to the nearest mm as follows: fishes (total length); crabs (carapace width); lobster ( Homarus americanus) (rostrum to tail length); and blue mussel (shell length).


Statistical Analysis

The statistical comparison of colonization plates involved using Bartlett's Test for Homogeneity to determine if treatment variances were uniform. Non-parametric, non-uniform data was log transformed before running ANOVA. For species that exhibited statistically significant differences in biomass among the various plate materials, a Tukey's Multiple Comparison Test was conducted.



RESULTS

Nomenclature

The taxonomic classification and common and scientific nomenclature of marine life identified in this study are presented in Table 2.


Table 2

Mean abundance and biomass per m2 of species colonizing 15 experimental reef habitats after 24 - 96 months on the seafloor.

Microsoft Excel format Click link for table

Sample Size

Between 1998 and 2004, 15 experimental reef habitats were retrieved and analyzed as follows:

Year Number of Units
1998 1
1999 3
2000 3
2001 3
2002 2
2003 3
2004 3

These 15 units contained a total of 118 colonization plates including rock, concrete, steel and rubber. The plates were also separated into two treatments - inside and outside the mesh box. The numbers of plates sampled by material and treatment are as follows:

Material Inside Outside
Rock 15 14
Concrete 14 15
Steel 15 15
Rubber 15 15

For comparative purposes with other studies, the results concerning both the entire unit and the colonization plates were expanded to a m2 base. In the case of the entire unit, results were extrapolated to a m2 of sea floor footprint. For colonization plates, results were extrapolated to a m2 of surface area. The expansion factors used to extrapolate survey findings to the appropriate m2 base are as follows:

Habitat Component Expansion Factor (Range)
Experimental habitat
Colonization plates:
8.4-10.1
Rock 21.7-57.1
Concrete 14.4-21.8
Steel 24.4-26.9
Rubber 29.2-45.7

Species Diversity

During the 96-month study, a total of 145 different taxa were identified on the experimental reef units (Table 2; Figure 17). All of the phyla encountered were from the Kingdom Animalia; no plant taxa were observed on the experimental habitats. A total of 126 genera (Figure 18) and 99 species (Figure 19) were identified. The taxa included representatives from 9 phyla. In terms of identified taxa, the most diverse phyla included molluska (43), arthropoda (42), and annelida (37) (Table 2). The habitats included 7 colonial and 138 individual-organism taxa; 50 sessile and 95 mobile (1 unknown) taxa; and 9 vertebrate and 136 invertebrate taxa. There were 46 taxa strongly associated with sediments that were probably present in the experimental habitats due to their subsidence into the sandy sea floor; these taxa included 21 molluska, 14 arthropoda, 8 annelida, 1 cnidaria, 1 echinodermata and 1 nemata.

Total number of taxa inhabiting experimental reef habitats analyzed during 1998 through 2004
Figure 17. Total number of taxa inhabiting experimental reef habitats analyzed during 1998 through 2004

Between 1998 and 2004, the number of taxa identified on the experimental reef habitats rose from 39 to 145 (Figure 17).Although the absolute number of taxa identified throughout the survey continues to rise, the number of new taxa discovered each year declined after 1999. New taxa are generally represented by a small number of individuals that provide community diversity, but do not constitute a significant portion of the overall community biomass. The slope of the curve suggests that only a small number of new taxa will be identified over the next few years on the experimental reef habitats.


Abundance and Biomass

During the 96-month study, the mean abundance and biomass of marine life inhabiting 15 experimental reef habitats are summarized in Table 2. The abundance of colonial species was measured in terms of surface area coverage; the mean coverage of all colonial species amounted to 87,564 + 8,446 (SE) cm2 per m2 of unit footprint. Individual organisms were counted; the mean abundance of individual organisms was 534,567 + 109,191 per m2. Over the course of the 96-month survey, only 2 taxa (blue mussel and skeleton shrimp) numbered more than 100,000 individuals (Table 3). Only 35 percent of the taxa were represented by more than 100 individuals per m2.


Table 3

The relative mean abundance of individual organisms by taxa per m2 footprint of experimental reef habitat during 1998 - 2004. This table does not include colonial organisms.

Log of Abundance
per m
2
Range Number
of Taxa
Percentage
-1 0.1 - 0.9 12 9
0 1 - 9 32 23
1 10 - 99 46 33
2 100 - 999 24 17
3 1,000 - 9,999 16 12
4 10,000 - 99,999 7 5
5 100,000 + 2 1

Total number of taxa identified at least to generic level inhabiting experimental reef habitats for sampling years 1998-2004
Figure 18. Total number of taxa identified at least to generic level inhabiting experimental reef habitats for sampling years 1998-2004

Total number of taxa identified to specific level inhabiting experimental reef for sampling years 1998-2004
Figure 19. Total number of taxa identified to specific level inhabiting experimental reef for sampling years 1998-2004


The mean total damp weight biomass of all marine life averaged 84,175 + 11,992 g per m2 of experimental reef habitat footprint over the course of the survey. Molluska was the dominant phylum, representing 66.8 percent of the total unit biomass, followed by arthropoda (15.0 percent) and cnidaria (9.3 percent) (Figure 20). Other important phyla included ectoprocta (2.0 percent), annelida (3.0 percent), echinodermata (2.7 percent) and chordata (1.2 percent). Nemata and porifera represented a combined total of less than 0.1 percent of the overall biomass.

For molluska, blue mussel was by far the dominant species in terms of biomass, followed by two species of slipper shells (Figure 21). The arthropoda were dominated by a sessile genus, barnacle, and a mobile species, Jonah crab ( Cancer borealis) (Figure 22). Although 9 species of fish were captured on the habitats, cunner ( Tautogolabrus adspersus) was by far the most numerous and comprised the greatest combined biomass (Figure 23). During all sampling years combined, the mean number of fish was 105.7 + 9.6 per m2. This number included only small fish, less than 165 mm in TL, that were able to swim through the 2.5 cm square mesh. Most of these were juvenile fish. The actual number of small fish inhabiting the experimental habitats may be much greater, since some fish congregating outside the unit may have been scared away by the divers. Divers observed large, adult fish retreat from around the experimental habitats at their approach. Food and game species included black sea bass ( Centropristis striata), with a mean abundance of 3.1 fish per m2, tautog ( Tautoga onitis) at 0.6 fish/m2 and ocean pout ( Macrozoarces americanus) at 1.3 fish/m2 (Table 2).

Mean standing stock biomass (g/m<sup>2</sup>) of all marine life taxa colonizing experimental reef habitats by phyla, 1998-2004
Figure 20. Mean standing stock biomass (g/m2) of all marine life taxa colonizing experimental reef habitats by phyla, 1998-2004

Mean standing stock biomass (g/m<sup>2</sup>) of molluscan species inhabiting experimental reef habitats, 1998-2004
Figure 21. Mean standing stock biomass (g/m2) of molluscan species inhabiting experimental reef habitats, 1998-2004

Mean standing stock biomass (g/m<sup>2</sup>) of arthropod species inhabiting experimental reef habitats, 1998-2004
Figure 22. Mean standing stock biomass (g/m2) of arthropod species inhabiting experimental reef habitats, 1998-2004

Mean standing stock biomass (g/m<sup>2</sup>) of juvenile or small fish species inhabiting experimental reef habitat units, 1998-2004
Figure 23. Mean standing stock biomass (g/m2) of juvenile or small fish species inhabiting experimental reef habitat units, 1998-2004


Arthropoda are important forage species for marine food and gamefish. The mean abundance of arthropoda was 198,867 + 72,651 individuals per m2 of unit footprint. Ten species of crab accounted for a mean of 4,639 + 1,054 individuals per m2. All life stages of crabs, from megalops larvae to adults, were present within the units. Some Jonah and rock crabs ( Cancer irradians) had grown so large (over 40 mm carapace width) that they could not pass through the mesh and spent their entire lives inside the small, experimental habitats. The small cavities within the units provided escape cover for juvenile American lobster, which had a mean abundance of 14.9 + 3.7 individuals per m2.

The mean standing stock biomass of all taxa inhabiting experimental reef habitats fluctuated between 35,717 and 152,802 g/m2 of unit footprint during the 6 sampling years, with 2003 showing the greatest biomass (Figure 24). Colonial organisms showed a steady increase in biomass between 1988 and 2001, then declined in abundance over the next three years, while individual organisms varied from year to year, but exhibited a general increase over the 8-year study and accounted for most of the variation in community biomass between years (Figure 25). There was little living space available for additional colonization. The habitats were so tightly packed with marine life during the 2003 and 2004 collections that the 2003 collection, which was the largest, was probably near the maximum carrying capacity of the habitat.

Annual variations in biomass for 9 taxa are presented in Figures 26-34. Over the 8-year study period, mollusca, annelida and echinodermata exhibited a general increase in biomass. Arthropoda biomass increased steadily during the first 5 sampling years, but declined to its lowest level in 2004. Chordata exhibited its greatest biomass during 1998-2001, declining sharply to its lowest abundance in 2004. A possible explanation for this decline is the almost complete filling of the habitats' internal spaces by blue mussels, leaving little room for free-swimming fish. Porifera biomass varied considerably from year to year, which was unexpected given this phylum's slow growth rates and long life spans. Cnidaria, ectoprocta and nemata increased in biomass during the first half of the study and then declined thereafter.

Mean standing stock biomass (g/m<sup>2</sup>) of all taxa on experimental reef habitats over time, 1998-2004
Figure 24. Mean standing stock biomass (g/m2) of all taxa on experimental reef habitats over time, 1998-2004

Mean standing stock biomass (g/m<sup>2</sup>) of all organisms colonizing experimental reef habitats by organism type and sampling year, 1998-2004
Figure 25. Mean standing stock biomass (g/m2) of all organisms colonizing experimental reef habitats by organism type and sampling year, 1998-2004

Mean standing stock biomass (g/m<sup>2</sup>) of mollusca on experimental reef habitats, 1998-2004
Figure 26. Mean standing stock biomass (g/m2) of mollusca on experimental reef habitats, 1998-2004

Mean standing stock biomass (g/m<sup>2</sup>) of arthropoda on experimental reef habitats, 1998-2004
Figure 27. Mean standing stock biomass (g/m2) of arthropoda on experimental reef habitats, 1998-2004

Mean standing stock biomass (g/m<sup>2</sup>) of annelida on experimental reef habitats, 1998-2004
Figure 28. Mean standing stock biomass (g/m2) of annelida on experimental reef habitats, 1998-2004

Mean standing stock biomass (g/m<sup>2</sup>) of nemata on experimental reef habitats, 1998-2004
Figure 29. Mean standing stock biomass (g/m2) of nemata on experimental reef habitats, 1998-2004

Mean standing stock biomass (g/m<sup>2</sup>) of echinodermata on experimental reef habitats, 1998-2004
Figure 30. Mean standing stock biomass (g/m2) of echinodermata on experimental reef habitats, 1998-2004


Mean standing stock biomass (g/m<sup>2</sup>) of chordata on experimental reef habitats, 1998-2004
Figure 31. Mean standing stock biomass (g/m2) of chordata on experimental reef habitats, 1998-2004

Mean standing stock biomass (g/m<sup>2</sup>) of porifera on experimental reef habitats, 1998-2004
Figure 32. Mean standing stock biomass (g/m2) of porifera on experimental reef habitats, 1998-2004

Mean standing stock biomass (g/m<sup>2</sup>) of ectoprocta on experimental reef habitats, 1998-2004
Figure 33. Mean standing stock biomass (g/m2) of ectoprocta on experimental reef habitats, 1998-2004

Mean standing stock biomass (g/m<sup>2</sup>) of cnidaria on experimental reef habitats, 1998-2004
Figure 34. Mean standing stock biomass (g/m2) of cnidaria on experimental reef habitats, 1998-2004


Colonization Plates

Over the 96-month study, 24 genera of sessile epibenthic invertebrates were found attached to the colonization plates, including 7 colonial and 17 individual genera. Although mobile invertebrates were also observed on the plates, they were not included in the plate analysis.

Half of the colonization plates were located on the outside of the habitats; the other half were located inside the mesh of the habitats. In terms of mean total biomass, colonization was greatest on concrete (765.8 g/m2), followed by steel (609.7 g/m2), rock (597.7 g/m2) and rubber (447.7 g/m2) (Table 4; Figure 35). For inside plates, colonization biomass was greatest on rock (3514.5 g/m2 ), followed by concrete (1548.8 g/m2), rubber (1730.1 g/m2) and steel (1220.1 g/m2). However, none of the differences between the materials of the inside plates was statistically significant (P=0.36); log transformation, ANOVA, indicating that marine life had equal success colonizing the four reef-building materials used in New Jersey (Table 5). Man-made materials (concrete, steel and rubber) were just as effective as a natural one (rock) in supporting colonization by encrusting marine life. While there was no statistically significant difference in total biomass among materials, Balanus spp. showed significantly higher biomass on rock and concrete than rubber and Bryozoa exhibited higher biomass on steel than on rubber (Table 6).


Table 4

A comparison of sessile epifaunal colonization of four common reef-building materials - concrete, rock, rubber, steel - for sampling years 1998 - 2004.

Species Concrete (N=29) Rock (N=29) Rubber (N=30) Steel (N=30)
g/m2 SD +/- SE> g/m2 SD +/- SE g/m2 SD +/- SE g/m2 SD +/- SE g/m2
Colonial
Astrangia poculata 37.9 74.3 13.8 2.3 8.5 1.6 1.2 5.4 1.0 27.3 76.8 14.0
Bryozoa 60.6 64.9 12.0 65.1 85.1 15.8 30.9 45.5 8.3 83.9 71.9 13.1
Haliclonia spp 2.9 3.6 2.5 <0.1 <0.1 <0.1 0.0 0.0 0.0 <0.1 0.2 <0.1
Hydractinia echinata 4.5 12.9 2.4 19.4 63.4 11.8 5.3 15.6 2.8 20.7 44.9 8.2
Hydrozoa 49.8 42.1 7.8 53.0 70.3 13.1 109.5 105.2 19.2 43.5 70.3 12.8
Microciona prolifera 0.0 0.0 0.0 <0.1 0.2 <0.1 0.0 0.0 0.0 0.0 0.0 0.0
Porifera 2.4 8.8 1.6 0.3 1.4 0.3 1.3 6.7 1.2 0.9 3.4 0.6
Subtotal 158.1 49.9 9.3 140.2 57.5 10.7 148.1 60.9 11.1 176.4 60.9 11.1
Individual
Amphitrite ornata 0.1 0.2 <0.1 <0.1 <0.1 <0.1 11.8 64.3 11.7 0.1 0.4 0.1
Amphitrite spp 0.0 0.0 0.0 0.2 1.1 0.2 0.1 0.6 0.1 0.0 0.0 0.0
Anomia simplex <0.1 0.1 <0.1 <0.1 <0.1 <0.1 0.1 0.6 0.1 0.0 0.0 0.0
Ascidiacea 0.0 0.0 0.0 <0.1 <0.1 <0.1 0.0 0.0 0.0 0.0 0.0 0.0
Balanus spp 184.8 228.9 42.5 173.1 328.0 60.9 55.4 92.9 17.3 152.2 232.1 43.1
Ceriantheopsis americana <0.1 0.2 <0.1 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
Clymenella torquata 0.0 0.0 0.0 <0.1 <0.1 <0.1 0.0 0.0 0.0 0.0 0.0 0.0
Crepidula fornicata <0.1 <0.1 <0.1 0.7 2.9 0.5 0.1 0.5 0.1 0.4 1.2 0.2
Crepidula plana 0.1 0.6 0.1 1.9 10.1 1.9 0.2 0.7 0.1 1.3 5.7 1.0
Crepidula spp 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 1.5 8.4 1.5
Hydroides dianthus 6.5 16.9 3.1 1.2 4.8 0.9 0.7 2.7 0.5 4.3 7.1 1.3
Hydroides spp 25.1 34.5 6.4 14.6 24.6 4.6 5.0 13.7 2.5 22.3 42.5 7.8
Metridium senile 420.8 631.8 117.3 357.0 594.7 110.4 299.7 485.7 88.7 184.1 306.4 55.9
Mytilus edulis 342.7 674.6 125.3 1,414.8 2,999.6 557.0 565.5 1,107.1 202.1 370.7 815.0 148.8
Pseudopotamilla reniformis 3.3 9.0 1.7 1.0 2.0 0.4 1.8 4.8 0.9 1.3 3.6 0.7
Pseudopotamilla spp 2.3 11.8 2.2 0.1 0.5 0.1 0.2 1.1 0.2 0.2 1.1 0.2
Sabellaria vulgaris 0.1 <0.1 <0.1 0.0 0.0 0.0 0.0 0.0 0.0 <0.1 <0.1 <0.1
Subtotal 985.8 253.7 47.1 1, 964.7 786.7 146.1 940.8 316.1 57.7 738.4 230.5 42.1
Total 1,143.8 221.1 41.0 2,105.0 681.5 126.6 1,088.9 275.2 50.2 914.9 201.6 36.8

On the inside plates, depending on the material, individual organisms represented 91 to 97 percent of the total biomass (Table 7). In contrast, on outside plates, colonial organisms were much more abundant and represented 27 to 46 percent of the biomass (Figure 36). The combined standing stock biomass on colonization plates of all materials declined between 1998 and 2000 and then increased substantially during 2001-2004 (Figure 37). During 1998-2000, colonial invertebrates increased in biomass and then leveled off during 2001-2004. Individual invertebrates declined in biomass during 1998-2000 and then increased sharply during 2001-2004 (Figure 38).

Mean standing stock biomass (g/m<sup>2</sup>) of all attached epibenthic invertebrates inhabiting colonization plates for sampling years 1998-2004
Figure 35. Mean standing stock biomass (g/m2) of all attached epibenthic invertebrates inhabiting colonization plates for sampling years 1998-2004

Mean standing stock biomass (g/m<sup>2</sup>) of individual and colonial attached epifauna on colonization plates by plate material for sampling years 1998-2004
Figure 36. Mean standing stock biomass (g/m2) of individual and colonial attached epifauna on colonization plates by plate material for sampling years 1998-2004

Mean standing stock biomass (g/m<sup>2</sup>) of attached epibenthic invertebrates inhabiting colonization plates for sampling years 1998-2004
Figure 37. Mean standing stock biomass (g/m2) of attached epibenthic invertebrates inhabiting colonization plates for sampling years 1998-2004

Mean standing stock biomass (g/m<sup>2</sup>) of individual and olonial attached epifauna on colonization plates by sampling year, 1998-2004
Figure 38. Mean standing stock biomass (g/m2) of individual and olonial attached epifauna on colonization plates by sampling year, 1998-2004


Table 5

Statistical analysis to identify significant differences in
epifaunal standing stock biomass on four reef substrates.

Species Non-Transformed Bartlett's Value Logarithmic
Transformed Bartlett's Value
Model
p-value
Astrangia poculata < 0.0001 * 0.0719 0.1528
Balanus sp. 0.0007 * 0.9665 0.0188 *
Bryozoa 0.0281 * 0.0178 * 0.0068 *
Hydrozoa 0.0001 * 0.2979 0.0513
Metridium senile 0.0545 N/A 0.5090
Mytilus edulis <0.0001 * 0.8958 0.5460
Composite of all species <0.0001 * 0.1835 0.3528

* = significant results



Table 6

Statistical comparison of standing stock biomass of two species, Balanus spp. and bryozoa, that exhibited significant differences in colonization of four reef substrates.

A. Balanus spp. (Acorn Barnacle)
Tukey Grouping Mean N Material
A 1.746 15 Rock
A 1.698 15 Concrete
B A 1.4651 15 Steel
B 0.7691 15 Rubber

B. Bryozoan
Tukey Grouping Mean N Material
A 1.6440 15 Rock
B A 1.1841 15 Concrete
B A 1.1819 15 Steel
B 0.7165 15 Rubber

Tukey's multiple comparison test results. Means with the same letter are not significantly different. A.) Balanus spp. (acorn barnacle) test results indicate significantly higher colonization rates on rock and concrete than on rubber. B.) Bryozoan test results show that the rate of colonization for steel significantly higher than rubber.




Table 7

A comparison of sessile epifaunal colonization of four common reef-building materials - rubber, steel, concrete and rock - located inside and outside of a 2.5cm mesh cage, 1998-2004.

Type Species Inside (N=59) Outside (N=59)
g/m2 SD +/- SE g/m2 SD +/- SE
Colonial
Astrangia poculata 7.2 32.5 4.2 27.1 70.1 9.1
Bryozoa 40.6 50.9 6.6 79.5 80.9 10.5
Haliclonia spp 1.4 9.5 1.2 0.1 0.5 0.1
Hydractinia echinata 13.8 44.6 5.8 11.2 35.7 4.6
Hydrozoa 33.5 41.4 5.4 94.8 95.3 12.4
Microciona prolifera <0.1 0.1 <0.1 0.0 0.0 0.0
Porifera 1.6 7.3 1.0 0.9 3.7 0.5
Subtotal 98.0 38.0 4.9 213.6 70.8 9.2
Individual
Amphitrite ornata 6.1 45.9 6.0 0.0 0.0 0.0
Amphitrite spp 0.2 0.9 0.1 0.0 0.0 0.0
Anomia simplex 0.1 0.5 0.1 <0.1 0.1 <0.1
Ascidiacea <0.1 <0.1 <0.1 0.0 0.0 0.0
Balanus spp 134.5 219.9 28.6 147.0 255.7 33.3
Ceriantheopsis americana 0.0 0.0 0.0 <0.1 0.1 <0.1
Clymenella torquata <0.1 <0.1 <0.1 0.0 0.0 0.0
Crepidula fornicata 0.5 2.1 0.3 0.2 0.7 0.1
Crepidula plana 1.7 8.1 1.0 0.1 0.7 0.1
Crepidula spp 0.8 6.0 0.8 0.0 0.0 0.0
Hydroides dianthus 1.8 5.7 0.7 4.6 12.3 1.6
Hydroides spp 12.0 24.0 3.1 21.4 37.0 4.8
Metridium senile 569.5 612.9 79.8 58.9 188.5 24.5
Mytilus edulis 1184.8 2268.2 295.3 155.1 455.1 59.3
Pseudopotamilla reniformis 1.1 3.1 0.4 2.6 7.1 0.9
Pseudopotamilla spp 0.1 0.8 0.1 1.2 8.3 1.1
Sabellaria vulgaris 0.0 0.0 0.0 <0.1 0.2 <0.1
Subtotal 1913.1 627.1 81.6 391.1 138.6 18.0
Total 2011.1 542.8 70.7 604.6 125.3 16.3

Predation

In an attempt to examine predation of the reef fouling community by large fish and crustaceans, colonization plates were located inside the mesh box and outside the mesh. The plates outside the mesh were open to predation by large, free-ranging predators; the plates inside the mesh were limited to predation from small predators living within the habitat. The data suggest that the level of predation on individual and colonial sessile epibenthos depended upon plate location. Combining all substrates over the 96-month study, the mean standing stock biomass of sessile individual epibenthos was significantly greater on the inside (1,941.7 g/m2) of the mesh as opposed to the outside (391.1 g/m2) (Student's t-test, Analysis of Means; T = 4.28; P > 0.995), suggesting that predation resulted in an 80 percent decrease in standing stock biomass (Table 7; Figure 39).

In contrast, the sessile colonial epibenthos was significantly greater (T = 4.43; P > 0.995) outside (213.6 g/m2) the mesh than inside (111.2 g/m2). The data were not collected in a manner that facilitated estimating an annual predation rate. The effects of the enclosed mesh box on water circulation, colonization of larvae, food distribution and consequent growth of epibenthos was not examined, but may have influenced these results. For individual organisms, Metridium abundance constituted the greatest disparity between inside and outside the mesh, followed by blue mussel. For the colonial epibenthos, hydroids and bryozoan made up the bulk of the difference, being much more abundant outside the mesh.

Mean standing stock biomass (g/m<sup>2</sup>) of individual and colonial attached epifauna on colonization plates by plate location for sampling years 1998-2004
Figure 39. Mean standing stock biomass (g/m2) of individual and colonial attached epifauna on colonization plates by plate location for sampling years 1998-2004


Observations

In an attempt to provide suitable habitat for a diversity of sessile and mobile invertebrates and vertebrates, the experimental habitats were designed to have a variety of substrates and a complex matrix of crevices and chambers. While the suitability of the experimental habitat probably varied among taxa and an optimum habitat was probably not achieved for any taxa, 145 identifiable taxa did use the experimental units as living space to some extent.

The wire mesh, probably because of its thin diameter and possibly its vinyl coating, did not provide a good attachment surface, except for hydroids and bryozoans.

While blue mussels attached to all of the colonization plates and internal substrates, large individuals were found in the secluded crevices of the corrugated panels and whelk shells and on the inside plates. On exposed surfaces, only YOY mussels were found in large numbers. This was most likely due to predation in exposed locations. Even when tucked inside the unit, water circulation was apparently sufficient to provide the necessary flow of planktonic food to these filter feeders. The survival and growth of blue mussels resulted in the species almost completely filling the volume of the experimental habitats with little room available for additional colonization. It appears that the 2003 samples are probably near the biological carrying capacity of the habitats.

Crabs, shrimps, juvenile lobsters and small fishes used the numerous holes and chambers for seclusion. The unit's large whelk shells provided exceptionally good homes for crabs and lobster. Unfortunately, whelk shells provide only short-term habitats due to the destructive activity of boring sponge and fan worms. After 96 months, the shells exhibited structure loss and were disintegrating. The honeycomb cavities of the corrugated panels were also used by these mobile species.

Over time, the experimental habitats slowly subsided into the sandy bottom. During the last collection, the lowest few centimeters of the panels were covered by sediment. Panels buried in sediment were devoid of epibenthic growth. The presence of nemata, surf clams ( Spisula solidissima) and other sea floor denizens in later-aged collections is undoubtedly due to the subsidence of the experimental habitats and the accumulation of sediment in the lowest portions of the units.

Depending upon species, fish used the experimental habitats as cryptic living space or escape cover. Conger eel ( Conger oceanicus), radiated shanny ( Ulvaria subbifurcata) and ocean pout probably lived in small crevices and holes; cunner, tautog and black sea bass, in contrast, schooled around the periphery of the habitat, scooting inside the protective mesh when disturbed by divers. The abundance of fish declined over time. This was probably due to reduced living space inside the habitats as blue mussels increased in size and filled the volume of the experimental habitats.



DISCUSSION

While most investigations regarding reef biology are focused on fish and a small number of harvestable macroinvertebrates, these animals, as upper-level consumers and in terms of species diversity, abundance and biomass, represent a relatively small portion of living reef communities. Danovaro et al. (2000) refer to such investigations as the top-down approach of examining reef community secondary productivity. Studying the largely overlooked components of a reef's biological community is far more important to understanding the overall productivity of a reef, its function as a food web and its influence upon the surrounding marine environment (Steimle et al. 2002). We constructed an over-simplified three-level food chain pyramid of the experimental habitat marine life community by lumping all sessile and sedentary invertebrates at the bottom, all mobile invertebrates in the middle and all fish species on the top. Small fish represented only 1.2 percent of the community, mobile invertebrates 11.3 percent and sessile and sedentary invertebrates, 87.5 percent. This comparison does not include adult (large) fish since they were not sampled in our survey.

Assuming 29.5 adult fish per m2 of reef habitat (Figley and Daetsch 2004) at an average weight of 100 g/fish, then (large + small) fish biomass would increase to 3,949 g/m2 and represent 4.5 percent of the total reef community biomass. Mobile invertebrates comprise 11.0 percent of total biomass. Even after adjusting biomass estimates to account for adult fish, sessile and sedentary epibenthos still account for 84.5 percent of reef community biomass (Figure 40). These encrusting organisms are dependent upon hard substrate and form the most important component of the reef community, forming a living carpet that is used as cover by mobile invertebrates, harnessing energy from the water column by filtering plankton and detritus and providing a substantial food resource for both fish and mobile invertebrates. Sessile marine life species were brought to the reef involuntarily as planktonic larvae; they did not actively seek out the reef as an attractive habitat. Thus, for the vast majority of reef denizens, reef structures provide productive, not attractive, habitats.

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).

Approximate reef habitat food chain relationships between fish, mobile invertebrates and sessile/sedentary invertebrates in terms of biomass 1998-2004
Figure 40. Approximate reef habitat food chain relationships between fish, mobile invertebrates and sessile/sedentary invertebrates in terms of biomass 1998-2004


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.

Study
Area
Dominant Species Mean Biomass (g/m2) Reference Enhancement ratio reef vs. sand
Off Barnegat Light NJ, area A, grab sampling Surf clam 463* Scott and Kelley, (1998) (Sept-Oct. 1997 sampling) 180
Clam dredge area A off Barnegat Inlet NJ Surf clam,
Moon snail
2384* Scott and Kelley (1998)
(1997 sampling)
35
Coastal NJ,
<30 m depth, grab sampling
Various polychaetes and small crustaceans 26 Steimle (1985)
(1 stat.) 1982-1985 data
3,200
Central NJ
20 m depth, grab sampling
Sand dollar 606 (summer)
329 (winter)
Steimle (1990) (station 17,
1979-1985)
137 (summer)
253 (winter)
Clam dredge area B, D and LBI reference Lesser amounts of Surf clam 74 (range 11-193)* Scott and Kelley (1998)
(1997 sampling)
1, 124
Long Beach Island NJ areas B and D, and LBI reference site Diverse mollusks and polychaetes 30
(range 26.8-32.5)*
Scott and Kelley (1998)
(1997 sampling)
2,773
Coastal NJ,
<30 m depth,
grab sampling
Various polychaetes and small crustaceans 26 Steimle (1985)
(1 stat.) 1982-1985 data
3,200

* = 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.



LIST OF TABLES

Table 1 Mean dimensions of 10 experimental reef habitats, 1998-2001
Table 2 Mean abundance and biomass per m2 of species colonizing experimental reef habitats after 24-96 months on the sea floor
Table 3 The relative mean abundance of individual organisms by taxa per m2 footprint of experimental reef habitat during 1998-2004
Table 4 A comparison of sessile epifaunal colonization of four common reef-building materials - concrete, rock, rubber and steel - for sampling years 1998-200
Table 5 Statistical analysis to identify significant differences in epifaunal standing stock biomass on four reef substrates
Table 6 Statistical comparison of standing stock biomass of two species, Balanus spp. and bryozoa, that exhibited significant differences in colonization of four reef substrates
Table 7 A comparison of sessile epifaunal colonization of four common reef-building materials - rubber, steel, concrete and rock - located inside and outside of a 2.5cm mesh cage, 1998-2004
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



LIST OF FIGURES

Figure 1 Experimental reef habitat
Figure 2 An experimental reef habitat ready for deployment
Figure 3 Top view of experimental reef habitat unit
Figure 4 Location of reef structures around experimental reef habitats
Figure 5 Thirty experimental habitats en route to the Barnegat Light Reef study site
Figure 6 Divers sent the encapsulated habitats to the surface using an air lift bag
Figure 7 Divers encapsulated the experimental reef habitat units inside a plastic drum, trapping most marine life inside
Figure 8 Retrieving an experimental reef habitat unit encapsulated in a plastic drum
Figure 9 The experimental habitat units were placed in a plastic collection pool before being dismantled
Figure 10 The wire mesh cage is cut open to access experimental substrates
Figure 11 The opened habitat unit showing whelk shells and corrugated panels
Figure 12 The opened habitat showing upper chamber
Figure 13 Marine life growth on whelk shell
Figure 14 Marine life growth on concrete colonization plates located outside mesh (top) and inside mesh
Figure 15 Marine life growth on rock colonization plates located outside mesh (top) and inside mesh
Figure 16 Marine life growth on rubber colonization plates located outside mesh (top) and inside mesh
Figure 17 Total number of taxa inhabiting experimental reef habitats analyzed during 1998 through 2004
Figure 18 Total number of taxa identified at least to generic level inhabiting experimental reef habitats for sampling years 1998-2004
Figure 19 Total number of taxa identified to specific level inhabiting experimental reef for sampling years 1998-2004
Figure 20 Mean standing stock biomass (g/m2) of all marine life taxa colonizing experimental reef habitats by phyla, 1998-2004
Figure 21 Mean standing stock biomass (g/m2) of molluscan species inhabiting experimental reef habitats, 1998-2004
Figure 22 Mean standing stock biomass (g/m2) of arthropod species inhabiting experimental reef habitats, 1998-2004
Figure 23 Mean standing stock biomass (g/m2) of juvenile or small fish species inhabiting experimental reef habitat units, 1998-2004
Figure 24 Mean standing stock biomass (g/m2) of all taxa on experimental reef habitats over time, 1998-2004
Figure 25 Mean standing stock biomass (g/m2) of all organisms colonizing experimental reef habitats by organism type and sampling year, 1998-2004
Figure 26 Mean standing stock biomass (g/m2) of mollusca on experimental reef habitats, 1998-2004
Figure 27 Mean standing stock biomass (g/m2) of arthropoda on experimental reef habitats, 1998-2004
Figure 28 Mean standing stock biomass (g/m2) of annelida on experimental reef habitats, 1998-2004
Figure 29 Mean standing stock biomass (g/m2) of nemata on experimental reef habitats, 1998-2004
Figure 30 Mean standing stock biomass (g/m2) of echinodermata on experimental reef habitats, 1998-2004
Figure 31 Mean standing stock biomass (g/m2) of chordata on experimental reef habitats, 1998-2004
Figure 32 Mean standing stock biomass (g/m2) of porifera on experimental reef habitats, 1998-2004
Figure 33 Mean standing stock biomass (g/m2) of ectoprocta on experimental reef habitats, 1998-2004
Figure 34 Mean standing stock biomass (g/m2) of cnidaria on experimental reef habitats, 1998-2004
Figure 35 Mean standing stock biomass (g/m2) of all attached epibenthic invertebrates inhabiting colonization plates for sampling years 1998-2004
Figure 36 Mean standing stock biomass (g/m2) of individual and colonial attached epifauna on colonization plates by plate material for sampling years 1998-2004
Figure 37 Mean standing stock biomass (g/m2) of attached epibenthic invertebrates inhabiting colonization plates for sampling years 1998-2004
Figure 38 Mean standing stock biomass (g/m2) of individual and colonial attached epifauna on colonization plates by sampling year, 1998-2004
Figure 39 Mean standing stock biomass (g/m2) of individual and colonial attached epifauna on colonization plates by plate location for sampling years 1998-2004
Figure 40 Approximate reef habitat food chain relationships between fish, mobile invertebrates and sessile/sedentary invertebrates in terms of biomass 1998-200



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Marine life colonization of experimental reef habitat
in temperate ocean waters off New Jersey, 1996-2004

New Jersey Department of Environmental Protection
Division of Fish and Wildlife
Bureau of Marine Fisheries


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