The influence of post-settlement processes on the structure of reef-fish assemblages
Anne-Marie Eklund, Alina M. S2mant, and James A. Pohnsack
Running head: Post-§ettlement processes affecting reef fish assemblages The influence of post-settlement processes on the structure of reef-fish assemblages
ABSTRACT
We used model reefs with varying amounts of habitat complexity and epibenthic
growth to test the effects of reef shelter and food resources on fish density, species richness,
biomass, size composition and species relative abundances. We visually censused the reef
fish assemblages on each model reef, monthly from September 1991 through December
1993, and estimated fish biomass through length/weight regressions from fish collections.
Reefs with different amounts of reef-based food resources did not support significantly
different fish assemblages; however, reef shelter had a significant effect on the fish
assemblage structure. High-shelter reefs sustained greater fish densities, but low-shelter
49 reefs supported greater fish biomass. The size and species composition varied between reef
types with a greater abundance of juvenile fishes on the reefs with more shelter from
predators. Although juvenile fishes less than 2 cm TL settled indiscriminately on all of the
model reefs, they did not persist on reefs lacking adequate shelter. Fishes from 2-1 0 cm TL
were. significantly more abundant on high-shelter reefs. The tightly coupled post-settlement
processes of predation and competition for limited shelter from predators greatly affected the
fish assemblage structure. Post-settlement predation and resource limitation, therefore, may
be more important than larval supply in regulating Caribbean/Atlantic reef fish assemblages.
I INTRODUCTION
Coral reefs are extremely complex habitats which support a high density and diversity of fishes. The mechanism(s) responsible for maintaining dense and speciose assemblages have been debated by many reef fish ecologists (e.g. see Doherty and Williams, 1988; Hixon,
1991; Jones, 1991; Sale, 1991). Determining the limiting factors of reef fish production is of interest to fishery managers and ecologists alike.
. For the past 20 years, there has been a greater emphasis in the literature on the stochastic and highly variable planktonic environment and its effects on larval fish survival and recruitment. Several studies have concluded that reef fish populations appear to be recruitment limited, which means that they are limited by processes that occur during the larval planktonic stages (Talbot et al., 1978; Victor, 1983,1986; Doherty and Williams, 1988;
Doherty and Fowler, 1994a,b). There is some evidence (Doherty and Williams 1988;
Doherty and Fowler, 1994a,b) that larval mortality rates are sufficiently high to reduce population numbers to the point where reef resources are not limiting. If population numbers are very low, then the amount of shelter or food on coral reefs would not be limited for reef fishes, and therefore, they would not be important variables in controlling fish populations and the resulting reef fish assemblage structure.
Although some species of pomacentrids on the Great Barrier Reef may be recruitment limited (Doherty and Fowler, 1994a,b), there is evidence that some families of fishes in the
Atlantic (e.g. Haemulidae) may be subject to high rates of post-settlcment predation
(Shulman and Ogden, 1987; Hixon and Beets, 1993). The amount of shelter available to those reef fishes may have a direct effect on their survival. Post-settlement predation may
2 be high enough io have an effect on overall population sizes and species relative abundances.
It is possible to assess the importance of reef resources in controlling fish assemblage structure and production by manipulating the amount of reef shelter or food available. If a
. reef fish population is limited by habitat, then a complex reef, offering more shelter, could support more fish, particularly small prey fish. Shulman (1984) found a significant relationship between shelter availability and the abundance of small prey fishes in the Virgin
Islands. The applicability of her experiments to large reef systems has been questioned, however, due to the very small scale of the model reefs that she used (conch shells) (Doherty and Williams, 1988). Hixon and Beets (1989, 1993) also studied the relationship between reef shelter and densities of different groups of fishes on artificial reefs in the Virgin Islands, but their results were inconsistent, possibly due to seasonal recruitment pulses. Neither
Shulman (1984) nor Hixon and Beets (1989,1993) examined changes in fish biomass as an indicator of fish production. By following patterns of fish density, species richness and biomass on larger experimental reefs monthly for over two years, we have been able to substantiate and expand upon the previous studies' conclusions.
To test whether increased shelter availability does increase reef fish populations, we compared model reefs having identical external structures but very different internal structures - low shelter (hollow) vs. high shelter (filled) reefs. Similarly, to test for the effect of reef food resources on reef fish populations, we compared reefs with identical structures but with different amounts of epibenthic growth. We measured changes in fish density, biomass, species richness and size and species composition on the different reef types. Our hypothesis was that fish density, biomass and species richness on high shelter or high food
3 reefs would be greater than on low shelter or low food reefs and that the frequency distribution of fish by species and by size class would differ among reefs with different shelter or food resources. By looking at fishes of different species and size classes, it was possible to determine if some target species are sensitive to changes in habitat quality or if the juvenile stages of some species are limited by habitat. This study improves upon previous ones, such as Shulman (1984) and 1-fixon and Beets (1989, 1993), by examining the ontogeny of shelter dependence, by conducting the study over a larger area and longer time period, and by further defining the relationships of different size classes and species to shelter resources.
METHODS
Study Site and Treatments
Twelve prefabricated concrete model reefs were used to provide four treatments of habitat complexity and food resources (three replicates per treatment). The reefs were deployed in 9 in of water ca. 500 in off the coast of Palm Beach, Florida in August 1991
(Figure I The pyramid shaped modules were 2.4 rn^ at the base, I in' at the truncated top
(which was open) and 1.8 in high (Figure 1). Along each of the four sides were 20 cm^ holes spaced 15 cm apart. The replicate reefs were placed 15 m apart along east-west transects, and each treatment was at least 400 in apart along a north-south axis parallel to the shoreline. The nearest natural reef areas were at least 250 in from the artificial structures.
To test for the effects of vay*g reef food resources on the fish assemblages, we attempted to manipulate epibenthic growth. One set of reefs (FF) was fertilized with
4 Osmocote(& fertilizer to increase growth of attached epiflora. A second set (PF) was painted with anti-fouling paint to reduce the amount of epibenthic growth on the exterior surfaces.
A third set (CF) was not manipulated. All three of these reef sets were filled with large pieces of broken cinder blocks. The blocks were placed inside the pyramids haphazardly, creating interstices of many sizes for small, cryptic fishes to inhabit. The reefs of the remaining set were not filled with cinder blocks and remained hollow structures (H). The hollow and filled reefs were compared to test for effects of reef shelter on the fish assemblages.
Fish Censuses
Fish density, size frequency, and species composition were determined through monthly visual censuses at each reef. An open sandy site between the fertilized and the control reef treatments was also censused in order to compare the reef fish assemblages with those on non-reef areas. The visual survey method was adapted from Bohnsack (1979), in which all fish on each reef are counted and measured by scuba divers. PVC rods with 30 cm rulers attached enabled divers to measure individual fish. Divers counted and measured all of the highly mobile species first, followed by closely examining the reef holes and crevices for the cryptic species. These surveys were supplemented by a night dive, so that the nocturnally active species could be observed. Because these model reefs are small isolated structures, it was possible to count and measure all of the fish seen, precluding the use of other visual techniques which "subsample" fishes on larger natural reefs.
Fish Biomas
In September 1993, one reef from each treatment was poisoned with rotenone, and
5 all fish were collected and measured for the development of length/weight relationships for each species. Prior to the rotenone sampling, each reef was censused visually in order to determine the biases or limitations of the visual censuses. Divers then encircled each reef with a 4.6 in radius cast net, by beginning upstream and slowly swimming downstream towards the reef with the outstretched net. In this way, those schooling species,that fed upstream from the reef (e.g. haemulids) were corralled as they sought the shelter of the reef.
A 0.65% solution of pure rotenone was quickly sprayed into reef crevices, and divers collected fish as they expired. One diver remained above the reef with a net to intercept those very small fish that escaped through the cast net's mesh. Lengthtweight regressions for each species are listed in Table 1.
Natural Reefs
Assessments of representative fish assemblages for the area were done by censusing fish density and species composition on patch reefs within 500 rn of the model reef sites. The stationary census method used for the natural reefs was taken from Bohnsack and Bannerot
(1986), where all of the fish observed in 5 minutes were identified, counted and measured.
Each month, from July through September, 1994, three replicate censuses were made on natural reefs, and on the same dates, the three replicates of fertilized filled and hollow reefs were censused. The natural reef was in 9-10 m of water with a vertical relief of I m. It was an area of rocky overhangs with some gorgonians, hard corals and sand patches, along with areas of rock and rubble.
Data Analysis
The differences between reef treatments and reef relative locations (inshore, middle,
6 offshore) in fish density, biomass, species richness, the densities of each size class and the densities of the more abundant species were tested using the non-parametric Kruskall-Wallis test, since variances for some comparisons were heterogeneous. Species density comparisons were done for the 14 overall most abundant species or species groups. Species groups were used when we were not certain that all observers properly identified the species within that group. For example, the identification of small juvenile drums such as high-hat
(Equetus acuminatus), jackknife-fish (E. lanceolatus), spotted drum, E. punctatus, and cubbyu (E. unibrosus) may have been misidentified by some of the divers; therefore, the
Equetus spp. were combined in one species group for analysis. For all tests for significance, we used an alpha level of 0.05.
RESULTS
Reef Fish CoMmunily Description
A total of 151 species, representing 36 families, was observed on the model reefs during 23 monthly censuses from September 1991 through December 1993 (Table 1). More serranids, holocentrids, apogonids, muracnids, and Equetus spp. were observed at night
(Eklund 1996); therefore, it is reasonable to assume that these species were underestimated in the visual census data.
The mean number of fish and species (+/- 1 S.E.) was highest on the control filled
(CF) re efs and lowest on the hollow (H) reefs (Table 2A). The number of species per reef was correlated with the number of individuals. The CF reefs had significantly greater fish biomass than any of the other reefs (Table 2A), and the biomass on the H reefs was
7 significantly greater than on tile feriflized filled (FF) and painted filled (PF) reefs (Table 2A).
All reef treatments had significantly more fish, more species and greater biomass than the
open sand bottom site did. The number of fish, number of species and fish biomass was
greater on the offshore reefs than on the middle or inshore reefs (Table 2B), although these
relationships were not significant -for all reef treatments.
Rotenone Smples vs. Visual Censuses
A more complete description of the model reef fish assemblages was possible after
collecting fish with rotenone, since the cryptic species, such as muraenids, serranids,
apogonids, blenniids, clinids, gobids, and small sciaenids and scarids, were overlooked in
the visual censuses (Table 3). The species richness was greater in the rotenone samples than
in the visual censuses for all reefs except the hollow reef (Table 3). The hollow reef did not
support as many cryptic species, and not as many fish escaped visual detection. Mobile
species, such as the lutjanids, acanthurids, balistids, carangids, sparids and some of the
haermilids, escaped the rotenone sampling (Table 3). Where large schools of juvenile
haermilids were present, the visual estimates either overestimated (on the H reef) or underestimated (on the PF reef) their numbers (Table 3).
A comparison of the mean total length (TL) of each species observed in the visual
censuses with the mean TL measured for each species from the rotenone samples shows that visual censuses underestimated true length; therefore, the biomass is underestimated (Figure
2). Linear regression of estimated TL on measured TL resulted in the following equation for all species combined (N=44, r--0.82):
visual estimate of TL = 2.331 + 0.561 (measured TL).
8 Since the CF reefs had a greater incidence of largemobile species, the difference in biomass
between that treatment and others is probably even greater than was estimated by visual
censuses.
CoWarison with Natural Reefs
In July and in September, 1994, the number of fish and number *of species observed on natural reef areas did not differ significantly from those on the filled or hollow model
reefs (Figure 3). In August 1994, however, the natural reefs had more fish and species than
the hollow reefs but did not differ in these regards from the filled reefs (Figure 3). The natural reef areas had significantly more mid-sized fish (6-20cm TL) and fewer small fish
(2-5cm TL) than found on either the hollow or filled reefs (Figure 4). Significantly more gray triggerfish (Balistes capriscurs) and bluehead wrasse (Thalassoma bifasciatum) were found on the model reefs, while the natural reefs had more sergeant major (Abudefduf saxatilis), smallmouth grunt (Haemulon chrysargyreum), French grunt (H. flavolineatum), and yellow goatfish (Mulloidichthys martinicus) than either model reef treatments (Figure
5). In additi.on, the hollow reefs differed from the natural reefs by having significantly more porkfish (Anisotremus virginicus), greater ambedack (Seriola dumerili) and cardinalfishes
(Apogon spp.). The filled fertilized reefs had significantly more sailor's choice (H. parra) and margate (H. album) and fewer Pomacentrus spp., Acanthurus spp., and spottail pinfish
(Diplodus holbroola) thart the natural reefs (Figure 5). Although the depth range was similar for natural and model reefs, the natural reef area was 200 in closer to shore, which may have accounted for some of the species composition differences. Both the model and natural reefs supported high densities ofjuvenile fishes, the majority of which were Haemulan spp. The natural reef density of the most abundant baemulid, the tonitate (H. aurofineatum) was greater than the density on the model reefs, but the difference was not significant.
Choice of Control Treatmen
Attempts to increase productivity, and therefore reef food resources, by using fertilizer were unsuccessfiil, in that nutrient concentrations and epibenthos on the fertilized reefs did not differ significantly from those on any of the other reefs, excluding the PF treatment. Strong currents, moderately high local nutrient and plankton conditions resulted in the dominant cover to be fouling filter-feeding invertebrates (Szmant, Jacobson, and
Eklund, unpublished data). Fertilization was stopped after September, 1992. Given the lack of fertilization effect, the FF reefs should have been essentially the same treatment as the CF reefs.
However, there were significant differences between the control and fertilized reefs.
Fish density and biomass were significantly greater on the control reefs (Table 2A). The difference in fish density varied temporally (Figure 6) and was caused mainly by the presence of large schools of pelagic fishes on the control reefs during certain months (e.g.
March and July 1993). Although the difference in biomass was not significant in all months, mean biomass on the CF reefs was always greater than on the FF reefs (Figure 7). Species richness on both the FF and the CF treatments was not significantly different (Table 2A), with both reef types having a peak in number of species in August 1992 (Figure 8). There were significantly fewer fish from 2-5 cm TL and significantly more fish greater than 10 cm
TL on the CF reefs (Figure 9), which explains the greater biomass observed on the CF reefs.
It is evident that the CF reefs had a different fish assemblage than my of the other
10 reef treatments (Figure 10). Large numbers of carangids, primarily the round scad
(Decapterus punctatus), and gray triggerfish (Balistes capriscus), gray snapper (Lutjanus griseus), lanc snapper (L. synagris) and large haemulids (Haemulon album and Haemulon parra) only occurred on the CF reefs,
The CF reefs were several hundred meters away from the natural reefs and more isolated than the other model reefs (Figure 1), possibly resulting in a greater attraction potential for reef fish colonizers. Use of these isolated reefs as the control set would have provided an unfair comparison among reef treatments. In order to be more conservative in testing for differences among the other reef types, we chose to use the FF reefs as the control reefs to test for the effects of habitat complexity (comparison with hollow reefs) and food availability (comparison with painted reefs).
Habitat Compl=^^
There were significantly fewer fish on the hollow reefs than on any of the filled reefs
(Table 2A). Fish density varied greatly with season but the mean number of fish was almost always greater on the FF reefs than on the H reefs (Figure 6). Fish biomass, however, was greater on the H reefs than on the FF reefs (Table 2A, Figure 7), due to a few large individuals, especially on certain dates. For example, in Jan. 1992, fish biomass on hollow rr.efs was large due to four spadefish (Chaetodipterusfaber), two greater arnbe^ack (Seriola dumerih) and 20 spottail pinfish (Diplodus holbrooki). In Oct. 1992, 15 ambedack at 45 cm
TL were present, and in September 1993, large schools of 25 cm. TL blue runners (Caranx crysos) and 38 cm TL ambedacks were observed near the hollow reefs. %ile there were more species found on the FF reefs, this difference was greatest during a peak in species
11 richness in 1992 and was not significant overall (Figure 8). The size frequency of the fish assemblages differed between FF and H reef treatments, with significantly fewer small fish
(2- 10 cm TL) and significantly more mid-sized fish (1 1-20 cm TL) found on the hollow Ireefs (Figure 9). The 2-1 0 cm size range was dominated by juvenile haermilids, particularly the tonitate, Haemulon aurolineatum. Although unidentified haemulids (those less than 2 cm
TL) were present on all reef types in large numbers, tonitates were seen in significantly fewer numbers on the hollow reefs. Balistes capriscus, Pomacentrus spp., Luyanus synagris and
Equelus spp. were also found in significantly fewer numbers on the hollow reefs (Figure 10).
A major difference in species composition among reef types was the abundance of Diplodus holbrooki on the hollow reefs and its rarity on any of the other reef types (Figure 10).
Luyanus griseus was also found in significantly greater numbers on the hollow reefs (Figure
10).
R=f--Based Food Resources
The anti-fouling paint was very effective in preventing any growth on the external structures of the PF reefs, even 3 years after reef placement (Figure 11). In spite of the obvious differences in reef-based resources, there were few differences in the reef fish assemblage between treatments. Fish density and fish biomass on the PF reefs were slightly lower, but not significantly so, than on the FF reefs (Table 2A, Figures 6 and 7.). Species richness was not significantly different either, with the FF reefs having more species in 1992 and the PF reefs having slightly more species in 1993 (Table 2A, Figure 8). The size composition of both reef types was similar (Figure 9) as was their species composition
(Figure 10). Out of the 14 most abundant species or species groups, only Thalassoma
12 bifasciatum, and Luyanus synagris were significantly more abundant on the FF reefs and
Abudefdufsaxatilis more abundant on the PF reefs (Figure 10).
DISCUSSION
It is clear from these results that increased shelter availability had a profound effect on many aspects of reef fish community structure. Important differences between high and low-shelter model reef types included a greater fish density and a greater abundance of juvenile fishes on high-shelter reefs. Contrary to what was expected, however, fish biomass was greater on the low-shelter reefs, mainly due to the more frequent presence of schools of carangids and the sparid, Diplodus holbrooki. Those transient species do not rely on reef shelter to any great extent and would not, therefore, be negatively affected by the lack of shelter. Rather, the foraging efficiency of the carangids and other transients may have been increased due to the lack of shelter available for resident prey fishes.
Cryptic species were collected on the high-shelter reefs in the rotenone samples
(Table 3) and were also observed on the high-shelter reefs during night censuses (Eklund,
1996). Since the low-shelter reefs did not support as many cryptic species, the difference in species richness, fish density and species composition between low-shelter and high-shelter reefs was probably much greater in reality than could be measured throughout the study via visual censuses.
Although the abundance of fish from the smallest size class, those under 2 cin TL, did not differ between high and low-shelter reefs, fish from 2-10 cm TL were found in greater numbers on the filled reefs. Newly settled haemulids made up the majority of the <
13 2 cm size class and were found on all reef types; therefore, they appeared to settle indiscriminately on the reefs. As the haemulids grew to 2 cm or more, most were identified as Haemulon aurolineatum. The abundance of H, aurolineatum was greater on the filled reefs, presumably due to an increase in survival from predators, because of the greater amount of shelter available. Successful emigration or immigration would have been unlikely, due to the degree of reef isolation. Small pornacentrids andjuvenile sciaenids were also found in greater abundance on the high-shelter reefs.
Reef food resources, on the other hand, did not appear to limit fish production, most likely due to the fact that the majority of the fish were feeding in the water column, in the sand adjacent to the reefs and in the seagrass communities away from the reefs. Most of the fish in this experiment, therefore, relied on the reefs primarily for shelter and to a lesser extent, if at all, for food. Even the reef associated pornacentrids were not adversely affected by the reduced productivity on the painted reefs, probably because they were able to forage either on plankton or on invertebrates living inside the reefs. Since the reefs were painted with anti-fouling paint on the outside only, there was some epifaunal growth on the inner edges of the holes and on the cinder blocks inside the reefs. Thalassoma bifasciatum was one of only two species that were in reduced abundance, and thus appeared to be affected by the lack of epifaunal growth on the painted reefs. The reasons for the lower abundance of
Luyanus synagris and the greater abundance ofAbudefdufsaxatifis on the painted reefs are unclear, since neither species relies on reef epifauna as its primary food source.
Shulman (1984) used conch shells to separate and test for the effects of shelter resources and food availability on fish colonization, but that study was limited to a very short
14 duration (1 -3 months) and spatial scale (a I in' arrangement of conch shells). Results from
the present study -were similar to those from Shulman (1 984), in that shelter resources had
a significant effect on the reef fish assemblage structure, whereas the amount of food a reef
provided did not. This study substantiates Shulman's findings, but on a larger scale. In
addition, this study provides information on the abundances and the species and size
composition of predators as well as prey fishes. The conch shells in Shulman's study (1984)
supported only 3-8 species, whereas the species richness of the larger and more complex
model reefs in this study mimicked natural reefs in the area. When natural reefs and the
model reefs were censused on thesame dates, 15-3 5 species were observed per census on the
natural reefs and 14-27 species on the model reefs (Figure 313). The slightly greater species
richness of the former is assumed to be due to the larger absolute size of the natural reefs.
0 Reef isolation appears to have had an important role in fish community structure of
the model reefs. The effect was apparent on the more isolated control filled reefs, compared
to any of the other model reefs, and in the comparison of the offshore reefs with the middle
and inshore reefs within each treatment. The model reefs that were farther from the natural
reefs had more mobile, piscivorous fishes than those reefs closer to the natural reef areas.
The offshore replicates of each treatment were also farther away from the natural reefs and
had more fish, species and biomass than the reef replicates closer inshore. Since the model
reefs were small structures, it is not surprising that larger fishes would spend less time on
them when natural reefs were closer. Bohnsack (1979) found an interference effect on
artificial reefs placed close to larger natural reefs, causing a dampening in the number of
fishes found on the artificial reefs. Shulman (1985) also found a decrease in prey species as
15 the distance to larger reefs decreased.
Processes Re2ulatine Reef Fish Assemblages
Competitionfor limited resources
Many studies have demonstrated positive relationships between reef habitat resources and fish density and diversity (de Boer, 1978; Luckhurst and Luckhurst, 1978; Gladfelter et aL, 1986; Anderson et al., 198 1; Shulman, 1984; Alevizon et al., 1985; Hixon and Beets,
1989,1993; Connell and Jones, 1991; Pitts, 1991). Jones (1987) and Forrester (1990) found evidence of density-dependent effects on reef fish recruits, with slower survival and maturation rates when recruit densities were high. The positive relationship between habitat resources and fish density, along with the evidence of density dependent growth dynamics, support the hypothesis that the coexistence of many reef fish species is possible due to habitat diversification and resource partitioning (see Smith and Tyler, 1973, 1975; Smith,
1978). However, there have been very few controlled experiments designed to elucidate the mechanisms involved in community regulation (reviewed in Ross, 1986). In addition, some studies have found no relationship between habitat variables and fish assemblage structure
(Talbot et al., 1978; Sale and Douglas, 1984), leading to a more critical evaluation of once- accepted dogma that coral reef fish communities are controlled by deterministic processes, primarily through competition for limited resources.
On coral patches in the Great Barrier Reef system, Sale (1975, 1977), Sale and
Dybdahl (1975) and Sale and Douglas (1984) noticeda lack of niche diversification along with a lack of any temporal stability in species composition. They described a "lottery" theory and concluded that reef fish assemblage structure is dependent upon stochastic events
16 in a non-equilibrium state. Others have criticized the lottery theory (e.g. Ogden and
Ebersole, 198 1, Gladfelter et al., 1980) saying that the results of many of those experiments
were artifacts of scale and that observations of fish communities on large natural and
artificial reefs over a period of many years demonstrated stable patterns of communities at
equilibrium.
Recruitment limitation
Both of the preceding theories, resource partitioning and lottery theory, assume that
competition for reef resources is the underlying process controlling the dynamics of fish
assemblages. In recent years, however, researchers have sbifted their focus to the theory of
recruitment limitation, and many papers have described the importance of pre-settlement
processes in determining the structure of fish assemblages on coral reefs (Victor, 1983;
0 Richards and Lindeman, 1987; Doherty and Williams, 1988; Milicich et al., 1992; Meekan
et al., 1993; Doherty and Fowler, 1994a,b). Although most of these studies have been
descriptive in nature, rather than' experimental, the correlative evidence for recruitment
limitation appears strong.
However, the influence of larval supply on reef fish assemblage structure cannot be
differentiated from that of post-settlement predation in many studies. For example, Doherty
and Fowler (1994a,b) reported that patterns evident in pre-settlement fish abundances may
be conserved after transition to the benthic life phase, and in some cases, year class strength
and patterns of variability were evident for years. Doherty and Fowler (I 994ab), however,
estimated the number of settlers by censusing juvenile pomacentrids on patch reefs 2-5
months after settlement. Thus, densities could either be due to pre-settlement events or post-
17 settlement processes or both. Since there is evidence that mortality can be highest in the first weeks and months of benthic life (Shuhnan and Ogden, 1987; Connell and Jones, 1991;
Sweatman, 1993), then post-settlement mortality estimates could vary widely, depending on how soon after settlement the fishes were censused. Doherty and Fowler (1994ab) assumed that mortality would be constant across large areas, but sources of mortality can change as fishing pressure or other disturbances alter the relative abundances of predators and prey.
Doherty and Fowler (1994ab) did show that events occurring before 5 months of age determine adult densities, but they did not prove which mechanisms were the determinants.
Larval supply limitation, post-settlement predation, interspecific competition or intraspecific compensatory effects may all have occurred and determined population sizes before these fishes were censused.
Milicich et al. (1992), found a correlation between pre- and post-settlement numbers on the scale of a reef system, but on the smaller habitat scale they found more variability between pre- and post-settlement distribution, indicating effects of post-settlement processes.
Victor (1986) found bluehead wrasse limited by recruitment, yet he documented micro- habitat preference and selection by new bluehead settlers. Williams et al. (1994) also documented habitat selection at settlement, resulting in different patterns of distribution than would have occurred based on recruitment variability alone.
Post-settlement predation
Leggett and DeBlois (1994) reviewed the literature for evidence of recruitment limitation and found that juvenile mortality could not be excluded from consideration as important in regulating year-class strength. Although there was often a positive relationship
18 between egg and larval abundances and recruitment, density-dependent juvenile mortality was significant in many st udies (Leggett and DcBlois, 1994). Shulman et al. (1983),
Shulman and Ogden (1987), Connell and Jones (199 1), Sweatman (1993), and Bohnsack et al. (1 994) have all indicated that newly settled recruits may be subject to intense predation.
Whether this post-sett.lement mortality is an important determinant in the structure of coral reef fish assemblages needs to be investigated further, although recent studies have supported this idea (Jones, 1990; Caley, 1993; Carr and Hixon, 1995; Eklund, 1996; Steele, 1997).
This study presents new evidence for post-settlement predation limiting recruit densities. In support of Hixon and Beets (1993) it demonstrates that recruits settled indiscriminately on all reef treatments but were then subjected to different levels of presumed mortality, corresponding to the amount of shelter available. The effect of increased shelter on small fishes was not consistent in Hixon and Beets (1993) for all experiments and much of the haemulids' responses were during short recruitment pulses. The present study, however, clearly documents, through monthly censuses each year of haemulid recruits on the different reef treatments, that the persistence of haermilids differs significantly on reefs providing different amounts of shelter micro-habitat. If these fishes were primarily recruitment limited, then the availability of adequate shelter would not have substantially affected their population numbers. It is likely that strong prevailing currents provided a continuous supply of recruits to this area of the Florida reef tract. Post-settlement predation and the availability of adequate shelter, rather than larval supply, appeared to be regulating the survival of new recruits.
This study supports the conclusions of Shulman (1 984) and Hixon and Beets (1989,
19 1993) that the availability of shelter from predators limits fish density and changes species
composition. It has strengthened their conclusions by showing that the conclusions hold up
over a longer time scale and with a larger model reef area than used by Shulman (1 984), and
by encompassing more frequent censuses and more species-specific analyses than presented
in Hixon and Beets (1989, 1993). The monthly censuses reported here over 28 months
include species and size specific information on all prey and predators present on the reef
treatments. These model reefs, filled with varying sizes and shapes of concrete blocks, more
realistically approximated the complexity of natural reefs.
In conclusion, the results of this study along with those of Shulman (1 984), Shulman
and Ogden (1987), and Hixon and Beets (1989, 1993) make a solid argument that post-
settlement factors such as shelter availability and predation can have a significant effect on
0 fish density, species relative abundances, and juvenile fish survival. Predation and
competition for limited shelter are tightly coupled processes controlling the ultimate reef fish
assemblage composition. Directed experiments to quantify the effects of predation (Jones,
1990; Carr and Hixon, 1995; Eklund, 1996; Steele, 1997) are the next step in elucidating
mechanisms regulating reef fish assemblages.
ACKNOWLEDGMENTS
We gratefully acknowledge Palm Beach County's Department of Environmental
Resource Management, who financed the construction and deployment of the model reefs.
In particular we would like to thank J. Bishop, D. Carson, H. Rudolph, C. Vare and J.
Vaughn for faithfully assisting us in collecting data for the project. We especially would like
20 to recognize A Jacobson for her work on characterizing benthic production on the reefs.
We are grateful for donations from Scuba Club, International Paint Grace Sierra and No-
Nonsense Panty Hose. This work benefitted from the tremendous diving support we
received from T. Baynes, S. Bolden, D. Harper, J. Javech, D. McClellan, J. Nichols, S.
Sandorf, C. Yeung and M. Zwicker. We also would like to thank M.E. Clarke, N. Ehrhardt,
T. Lee, and C.R. Robins for their advice and suggestions. This research was part of a
doctoral dissertation with funding provided by Florida Sea Grant.
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(AME, JAB) National Marine Fisheries Service, Southeast Fisheries Science Center, 75
0 Virginia Beach Drive, Miami, Florida 33149.
(AME, AMS) University of Miami, Rosenstiel School of Marine and Atmospheric Science, .
4600 Rickenbacker Causeway, Miami, Florida 33149.
29 Table 1. Total number of each species observed on model reefs off Palm Beach,
Florida, U.S.A., from September 1991 through December 1993, with length-
weight formulae derived for each species (from Bohnsack and Harper 1988;
Eklund 1996). Species names are from Robins et al. (1991). An R
designates those species that were caught in rotenone samples but were never
observed during visual censuses. Weights are wet weight in grams. Lengths
are total lengths in cm, unless otherwise specified as Fl, (fork lengths in cm).
The formula used to convert lengths to weights is: Weight (g) = A x Total
Length (cm)'.
Species and common names (by family) Number observed TL-W formulae
A B
Rhincodontidae
Ginglymostoma cirratum nurse shark 4 0.011 2.892
Rhinobatidae
Rhiwbatos lentiginosus Atlantic guitarfish 2 0.001 2.672
Dasyatidae
Dasyatis americana southern stingray 21 0.001 2.672
Dasyatis sabina Atlantic stingray 1 0.001 2.672
Dasyatis sp. 5 0.001 2.672
30 Species and common names (by family) Number observed TL-W formulae
A B
Muraenidae
Enchelycore carychroa chestnut moray R 0.0002 3.527
Gymnothoraxfunebris green moray 5 0.004 2.856-
Gymnothorax miliaris goldentail moray I 0.011 2.574
Gymnothorax moringa spotted moray 4 0.001 3.158
Gymnothorax sp. I 0.0002 3.527
Gymnothorax vicinus purplemouth moray 18 0.0002 3.527
Exocoetidae
Hemiramphus brasifiensis ballyhoo 45 0.105 2.356
Holocentridae
Holocentrus adscensionis squirrelfish 11 0.087 2.560
Holwentrus sp. 8 0.087 2.560
Myripristisjacobus blackbar soldierfish 3 0.087 2.560
Fistulariidae
Fistularia sp. unidentified cometfish I 0.004 2.866
Scorpacnidae
Scorpaenaplumieri spotted scorpionfish 24 0.024 2.949
Triglidae
Prionotus rubio blackwing searobin 2 0.012 3.029
31 Species and common names (by family) Number observed TL-W formulae
A B
Serranidae
Centropristus striata black sea bass 57 0.065 2.468
Diplectrumformosum sand perch 18 0.011 3.078 (FL)
Epinephelus cruentatus graysby 29 0.011 3.104
Epinephelusfulvus coney 2 0.011 3.104
Epinephelus guttatus red hind 2 0.011 3.112
Epinephelus morio red grouper 2 0.012 3.035
Epinephelus sp. I 0.011 3.104
Hypoplectrus unicolor butter hamlet 79 0.011 3.182 (FL)
Rypticus m aculatus whitespotted soapfish I 0.005 3.407
Rypticus saponaceus greater soapfish 0.005 3.407
Rypticus sp. 2 0.605 3.407
Rypticus subbifrenatus spotted soapfish I 0.005 3.407
Serranus subligarius belted sandfish 93 0.014 3.048 (FL)
Serranus tabacarius tobaccofish 2 0.014 3.048 (FL)
Serranus tigrinus harlequin bass 8 0.014 3.048 (FL)
Serranus tortugarum chalk bass I 0.014 3.048 (FL) unidentified serranid I 0.014 3.048 (FL)
32 Species and common names (by family) Number observed TL-W formulae
B
Apogonidae
Apogon maculatus flarnefish 171 0.008 3.326
Apogonpseudomaculatus twospot cardinalfish 45 0.008 3.310
Apogon sp. 16 0,008 3.310
Carangidae
Caranx bartholomaei yellowjack 149 0.026 2.909 (FL)
Caranx crysos blue runner 2131 0.052 2.690 (FL)
Caranx hippos crevallejack 53 0.052 2.734 (FL)
Caranx ruber barjack 351 0.007 3.237 (FL)
Decapterus macarellus mackerel scad 100 0.007 3.237 (FL)
Decapterus punctatus round scad 8271 0.007 3.237 (FL)
Selar crumenophthalmus bigeye scad 12 0.007 3.237 (FL)
Seriola dumerili greater ambedack 950 0.032 2.809 (FL)
Trachurus lathami rough scad R 0.007 3.237 (FL)
unidentified carangid 466 0.007 3.237 (FL)
Lutjanidae
Luyanus analis mutton snapper 13 0.008 3.140
Luyanus apodus schoolmaster 3 0.008 3.140
LuIjanus buccanella blackfin snapper 31 0.008 3.140
33 Species and common names (by family) Number observed TL-W formulae
A
LuYanus griseus gray snapper 2241 0.008 3.140
Luyanusjocu dog snapper I 0.008 3.140
LuYanus mahogoni mahogany snapper 2 0.008 3.140
LuYanus sp. I 0.008 3.140
LuYanus synagris lane snapper 794 0.008 3.140
Ocyurus chrysurus yellowtail snapper 41 0.008 3.140
Haemulidae
Anisotremus surinamensis black margate, 35 0.014 3.051
Anisotremus virginicus porkfish 1362 0.014 3.051
Haemulon album margate 185 0.019 2.930
Haemulon aurolineatum torntate 24476 0.012 3.000
Haemulon carbonarium caesar grunt 4 0.019 2.930
Haemulonflavolineatum French grant 315 0.010 3.156
Haemulon macrostomum Spanish grunt 39 0.019 2.930
Haemulon melanurum cottonivick 662 0.013 3.000
Haemulonparra sailors choice 1283 0.019 2.930
Haemulonplumieri white grant 24 0.019 2.930
Haemulon sciurus bluestriped grunt 50 0.023 2.855
34 Species and common names (by family) Number observed TL-W formulae
A B
Haemulon sp. 20723 0.012 3.000
Inermiidae
Inermia vittata boga. 211 0.007 3.237 (FL)
Sparidae
Archosargus rhomboidalis sea bream 3 0.018 3.102(FL)
Calanius arctifrons grass porgy 4 0.044 2.818 (FL)
Calamus bajonado jolthead porgy 6 0.044 2.818 (FL)
Calamus calanius saucereye porgy 91 0.043 2.801 (FL)
Calamus sp. 29 0.043 2.80 1 (FL) 0 Diplodus argenteus silver porgy 21 0.018 3.102 (FL)
Diplodus holbrooki spottail. pinfish 658 0.018 3.102 (FL)
Lagodon rhomboides pinfish 5 0.010 3.250 (FL)
Sciaenidae
Equetus acuminatus high-hat 223 0.009 3.202
Equetus lanceolatus jackknife-fish 28 0.001 3.844
Equetus sp. 27 0.009 3.202
Equetus umbrosus cubbyu 65 0.009 3.202
Micropogonias undulatus Atlantic croaker 40 0.009 3.202
35 Species and common names (by family) Number observed TIW formulae
A B
Odontoscion dentex reef croaker 5 0.009 3.202
Mullidae
MOW& chthys martinicus yellow goatfish 3 0.002 3.663 (FL)
Pseudupeneus maculatus spotted goatfish 27 0.016 3.026 (FL)
Pernpheridae
Pempheris schomburgki glassy sweeper I 0.016 3.072 (FL)
Kyphosidae
Kyphosus sectatrix Bermuda chub I 0.017 3.080(FL)
Ephippidae
Chaetodipterusfaber Atlantic spadefish 85 0.092 2.684 (FL)
Chaetodontidae
Chaetodon capistratus foureye butterflyfish 2 0.022 3.190
Chaetodon ocellatus spotfin butterflyfish I 0.032 2.984
Chaetodon sedentarius reef butterflyfish 23 0.025 3.076
Chaelodon striatus banded butterflyfish 3 0.022 3.140
Pomacanthidae
Centropygi argi cherubfish I 0.043 2.858
Holacanthus bermudensis blue angelfish 15 0.031 2.899
36 Species and common names (by family) Number observed TL-W formulae I A B
Holacanthus ciliaris queen angelfish 17 0.034 2.900
Holacanthus tricolor rock beauty 7 0.043 2.858
Pomacanthus arcuatus gray angelfish 6 0.034 2.968-
Pomacanthusparu French angelfish 26 0,020 3.126
Pomacanthus sp. I 0.034 2.900
Pomacentridae
Abudefdufsaxatilis sergeant major 558 0.019 3.046
Chromis cyanea blue chrornis 10 0.057 2.287
Chromis enchrysurus yellowtail reeffish 6 0.057 2.287
Chromis multilineata brown chromis 10 0.057 2.287
Chromis scotti purple reeffish 30 0.057 2.287
Chromis sp. 65 0.057 2.287
Pomacentrus diencaeus longfin damselfish 2 0.023 3.000
Pomacentrusfuscus dusky daniselfish 132 0.023 3.000
Pomacentrus leucostictus beaugregory 266 0.020 3.009
Pomacentruspartitus bicolor damselfish 283 0.020 3.000
Pomacentrus planiftons threespot damselfish 8 0.015 3.182
Pomacentrus sp. 17 0.023 3.000
37 Species and common names (by family) Number observed TL-W formulae
A B
Pomacentrus variabilis cocoa damselfish 534 0.023 3.000
Cirrhitidae
Amblycirrhituspinas redspotted hawkfish I 0.003 3.427
Sphyraenidae
Sphyraena barracuda great barracuda 23 0.005 3.083
Labridae
Bodianus rufiis. Spanish hogfish 107 0.015 2.876
Decodon puellaris red hogfish 7 0.015 2.876
Doratonotus megalepis dwarf wrasse 1 0.013 3.038
Halichoeres bivittatus slippery dick 173 0.015 2.876
Halichoeres garnoti yellowhead wrasse 22 0.005 3.375
Halichoeres maculipinna clown wrasse 30 0.003 3.693
Halichoerespictus rainbow wrasse 4 0.015 2.876
Ralichoeres radiatus puddingwife 38 0.013 3.038
Hemipteronotus novacula pearly razorfish 3 0.048 2.243
Hemipteronotus sp. 2 0.010 j.000
Hemipteronotus splendens green razorfish 3 0.010 3.000
Lachnolaimus maximus hogfish I 0.020 2.988 (FL)
38 Species and common names (by family) Number observed TL-W formulae
B
Thalassoma bifasciatum bluehead 2394 0.012 3.001
Scaridae
Scartis croicensis striped parrotfish I 0.015 3.055
Scarus taeniopterus princess parrotfish I 0.033 2.709
Sparisoma atomarium greenblotch parrotfish I 0.012 3.028
Sparisoma aurofrenatum redband parrotfish I I 0.012 3.028
Sparisoma chrysopterum redtail parrotfish 1 0.012 3.028
Sparisoma radians bucktooth parrotfish 5 0.012 3.028
Sparisoma rubripinne redfin parrotfish 2 0.012 3.028
Sparisoma viride stoplight parrotfish 5 0.012 3.028
unidentified scarid 10 0.015 3.055
Clinidae
Labrisomus gobio palehead blenny I 0.017 2.760
Labrisomus nuchipinnis hairy blenny 11 0.017 2.760
Malacoctenus macropus rosy blenny 4 0.025 2.223
Malacoctenus triangulatus saddled blenny 14 0.007 3.188
Paraclinusfasciatus banded blenny 2 0.017 2.760
Starksia ocellata checkered blenny R 0.011 3.003
39 Species and common names (by family) Number observed TL-W formulae
A
Blenniidae
Hypleurochilus geminalus crested blenny 1 0.017 2.760
Ophioblennius atlanticus redlip*blenny 3 0.032 2.379
Parablennius marmoreus seaweed blenny 117 0.017 2.760
unidentified blenniid/clinid 110 0.017 2.760
Gobiidae
Coryphopterus dicrus colon goby 1 0.009 3.000
Coryphopterus glaucofraenum bridled goby 62 0.009 3.000
Gnatholepis thompsoni goldspot goby 3 0.004 3.767
Gobiosoma genie cleaner goby 7 0.008 3.137
Gobiosoma horsti yellowline goby 14 0.008 3.137
Gobiosoma oceanops neon goby 5 0.008 3.137
unidentified gobiid 26 0.008 3.137
Acanthuridae
Acanthurus bahianus ocean surgeon 119 0.005 3.591
Acanthurus chirurgus doctorfish 706 0.005 3.591
Acanthurus coeruleus blue tang 300 0.005 3.591
Bothidae
Bothus lunatus peacock flounder 5 0.010 3.189
40 Species and common names (by family) Number observed TL-W formulae
I A B
Paralichthys albigutta gulf flounder 3 0.010 3.189
unidentified bothid 7 0.010 3.189
Balistidae
Aluterus schoepfi orange filefish 5 0.093 2.344
Aluterus scriptus scrawled filefish 7 0.823 1.814
Balistes capriscus gray triggerfish 2544 0.025 2.935 (FL)
Cantherhines pullus orangespotted filefish 29 0.068 2.563
Canthidermis sufflamen ocean triggerfish 40 0.018 3.055 (FL)
Monacanthus hispidus planehead filefish 42 0.050 2.618
Ostraciidae
Lactophryspolygonia honeycomb cowfish I 0.005 3.346
Lactophrys quadricornis scrawled cowfish I I 0.175 2.263
Tetraodontidae
Canthigaster rostrata sharpnose puffer 44 0.019 3.189
Diodon hystrix porcupinefish 58 0.533 2.276
Sphoeroides spengleri bandtail puffer 2 0.011 3.267
unidentified juveniles 3190 0.012 3.000
41 Table 2. Number of fish, number of species and fish biomass (mean ± I standard
error) observed on experimental reefs off Palm Beach, Florida, U.S.A.,
during visual censuses from September 1991 through December 1993:
A. For each reef treatment. N= 69 censuses at each reef treatment (3
replicates censused on 23 separate dates), except for the painted reef
treatment where sample size = 68 censuses; and B. For each relative
position of the replicates, inshore, middle and offshore. N=92 censuses at
each position, (4 treatments censused on 23 separate dates), except for the
middle position, where sample size = 91 censuses.
A. Reef Number of Fish Number of Species Fish Biomass (kg)
Treatment Control Filled 408.74 ± 48.96 18.23 :1: 0.42 27.80 ± 5.55 Fertilized Filled 308.84 ± 42.80 17.58 ± 0.60 4.49 ± 0.53 Painted Filled 233.09 ± 27.97 16.60 ± 0.45 3.29 :L 0.28 Hollow 168.19 ± 23.82 15.94 ± 0.56 6.72 ± 0.85 Open Sand Site 39.72 ± 23.33 0.73 ± 0.12 0.96 ± 0.46
B. Reef
Position Inshore 216.71 ± 30.52 14.17 * 0.72 6.54 ± 1.00 Middle 223.00 ± 24.87 13.44 ± 0.66 7.12 ± 1.44 Offshore 270.71 :^ 33.31 14.88 ± 0.71 12.94 ± 3.37
42 Table 3. A comparison of the number of fish from each species observed in visual
censuses (V) with those collected on the same day in rotenone samples (R)
from model reefs off Palm Beach, Florida, U.S.A. on September 23 and
24, 1993. CF=control filled reef, FF=fertilized filled reef; H=hollow reef,
PF=painted filled reef.
REEF CF FF H PF SPECIES V R V R V R V R ,4budefduf saxatilis I 1 0 0 0 0 2 5 A canthurus chirurgus 0 0 0 0 3 2 4 4 Acanthurus coeruleus 1 0 0 0 1 0 3 1 Anisotremus surinamensis 0 0 0 0 1 0 0 0 Anisolremus virginicus 5 2 0 1 8 4 3 1 Apogon maculatus 0 0 0 3 0 0 1 3 Apogonpseudomaculatus 0 0 0 2 2 3 0 4 Apogon sp- 0 0 0 0 0 1 0 0 Balistes capriscus 7 2 4 3 1 0 1 0 Blenniidae/Clinidae 0 0 0 1 0 3 0 0 Bodianus rufiis 0 0 0 0 0 0 1 1 Calamus bajonado 0 0 0 0 0 2 0 0 Calamus calanius 0 0 2 0 5 0 1 0 Canthigaster rostrata 1 2 0 0 0 0 1 2 Caranx crysos 0 0 0 0 48 0 0 0 Caranx ruber 0 0 0 0 0 0 1 0 Coryphopterus dicrus 0 3 0 2 0 4 0 14
43 REEF CF FIT H PF SPECIES V R V R V R V R Coryphopterus glaucoftaenum 0 1 0 0 4 0 2 0 Coryphopterus sp. 0 0 0 0 0 0 0 1 Diplodus holbrooki 0 0. 0 0 14 0 1 1 Enchelycore carychroa 0 0 0 0 0 0 0 1 Epinephelus cruentatus 1 3 .1 1 0 0 0 0 Equetus acuminatus 0 0 0 0 0 0 0 1 Gnatholepis thompsoni 0 0 1 0 0 0 0 0 Gymnothoraxfunebris 0 1 0 0 0 0 0 0 Gymnothorax moringa 0 1 0 0 0 0 0 1 Gymnothorax vicinus 0 0 1 2 0 0 0 2 Haemulon album 0 1 1 1 8 0 3 0 Haemulon aurolineatum 1 9 0 1 140 85 150 343 Haemulon carbonarium 0 1 0 0 0 0 0 0 Haemulonflavolineatum 0 3 0 0 5 103 65 127 Haemulon melanurum 0 1 0 0 0 8 8 12 Haemulon parra 13 14 2 2 0 0 2 1 Haemulonplumieri 0 0 0 0 0 0 1 0 Haemulon sciurus 1 2 0 0 0 0 0 0 Haemulon sp. 82 80 0 0 100 35 0 0 Halichoeres bivittatus 0 0 9 7 2 0 0 0 Holocanthus bermudensis 0 0 0 0 0 1 0 0 Luyanus griseus 25 1 5 0 10 0 2 1 Luyanus synagris 1 0 0 0 0 0 0 0 Ogilbia cayorum 0 1 0 0 0 0 0 0
44 REEF CF FF H PF SPECIES V R V R V R V R Ophioblennius adanticus 0 0 0 0 0 0 1 0 Parablennius marmoreus 0 6 0 5 5 13 0 12 Pomacanthusparu 0 0 0 0 0 . 0 1 1 Pomacentrus leucostictus 4 0 0 2 1 1 7 1 Pomacentrus parlitus 0 0 0 2 2 2 1 2 Pomacentrus planiftons . 0 4 0 0 0 0 0 1 Pomacentrus sp. 0 1 0 0 0 0 0 6 Pomacentrus variabilis 2 1 5 4 1 1 0 0 Rypticus saponaceus 0 0 0 1 0 0 0 1 Seriola dumerili 6 0 0 0 0 0 0 0 Sparisoma atomarium 0 1 0 0 0 0 0 0 . Sparisoma auroftenatum 2 0 0 0 0 0 0 1 Sparisoma radians 0 0 0 1 0 1 0 0 Sparisoma viride 0 0 0 0 . 1 0 0 0 Sphyraena barracuda 0 0 0 0 0 0 1 0 Starksia ocellata 0 2 0 5 0 2 0 1 Thalassoma bifasciatum 21 5 10 7 12 2 2 2 Trachurus lathami 1 0 0 0 0 0 1 0 0 Unidentified juveniles 200 0 0 0 0 0 0 0
Total # individuals 374 149 41 53 374 274 265 554 Total # species 18 26 11 20 22 20 25 30
45 LIST OF FIGURES
Figure 1. A) Location of model reefs off the coast of Palm Beach, Florida, U.S.A.
and B) an example of the reef modules, which rest in 9 rn of water.
Figure 2. Mean actually measured total length in cm (TL) for each species captured
via rotenone poison vs. mean visual estimate of TL for each species
observed prior to rotenone collection, in September 1993, on model reefs
off Palm Beach, Florida, U.S.A. The dashed line plots a perfect 1: 1
correlation between the two measures. The solid line describes the least
squares linear regression: Estimated Length = 2.331 + 0.561(Measured
Length), n = 44. r2= 0.82. The visual estimates, for the most part,
underestimated the actual length of the fish.
Figure 3. Number of fish (A) and species (B) (mean ± standard error) observed on
model and natural reefs off Palm Beach, Florida, U.S.A., in July, August
and September, 1994. H=Hollow model reefs; N=Natural coral reefs;
F=Filled model reefs. N=3 replicate reefs for each reef type. Dashes
denote significantly lower numbers than the natural reefs.
Figure 4. Number of fish on a log scale (mean ± standard error) for each of six size
classes in cm, observed on filled model reefs, natural coral reefs and
46 hollow model reefs off Palm Beach, Florida, U.S.A., in July, August and
September, 1994. Asterisks denote significantly greater numbers, when
comparing the natural reefs to the model reefs.
Figure 5. Number of fish on a log scale (mean ± standard error) for the most
abundant species or species groups found on hollow and filled model reefs
off Palm Beach, Florida, U.S.A. and on a natural coral reef area 500 in
adjacent to the model reefs, in July, August and September, 1994.
Asterisks (*) denote significantly greater numbers and dashes (-) denote
significantly smaller numbers when natural and model reefs are compared.
The species or species groups shown include: tonitate (Haemulon
aurolineatum), unidentified juveniles (newly settled), Decapterus sp.
(carangids), Balistes capriscus (gray triggerfish^, Thalassoma bifasciatum
(bluehead), Lu1jamis griseus (gray snapper), H album and H parra
(margate and sailors choice combined), Anisotremus virginicus (porkfish),
Pomacentrus spp. (damselfishes), Acanthurus spp. (doctorfishes),
Diplodus holbrooki (spottail pinfish), Abudefduf saxatilis (sergeant major),
cottonwick (Haemulon melanurum), smallmouth grunt (Haemulon
chrysargyreum), French grunt (Haemulonflavolinealum), bluestriped
grunt (Haemulon sciurus), yellow goatfish (Mulloidichthys martinicus),
Spanish hogfish (Bodianus rufus), greater ambeiJack (Seriola dumerili),
bar jack (Caranx ruber), blue runner (Caranx crysos), and Apogonidae
47 (cardinalfishes).
Figure 6. Number of fish on a log scale (mean ± I standard error) observed on
control filled (CF) model reefs (solid squares, long-dashed line), fertilized
filled (FF) model reefs (solid circles, dotted line), painted filled (PF)
model reefs (solid triangles, short-dashed line), and hollow (H) model
reefs (open circles, continuous line) off Palm Beach, Florida, U.S.A., for
each visual census, from September 1991 to December 1993. N=3 for
each reef/date.
Figure 7. Fish biomass in kilograms on a log scale (mean ± I standard error)
observed on control filled (CF) model reefs (solid squares, long-dashed
line), fertilized filled (FF) model reefs (solid circles, dotted line), painted
filled (PF) model reefs (solid triangles, short-dashed line), and hollow (H)
model reefs (open circles, continuous line) off Palm Beach, Florida,
U.S.A., for each visual census, from September 1991 to December 1993.
N=3 for each reef/date.
Figure 8. Number of fish species (mean ± 1 standard error) observed on control
filled (CF) model reefs (solid squares, long-dashed line), fertilized filled
(FF) model reefs (solid circles, dotted line), painted filled (PF) model reefs
(solid triangles, short-dashed line), and hollow (H) model reefs (open
48 circles, continuous line) off Palm Beach, Florida, U.S.A., for each visual
census, from September 1991 to December 1993. N=3 for each reef/date.
Figure 9. Mean number of fish, ± 1 standard error, for each of six size classes,
observed on control filled model reefs (cross-hatched bars), fertilized filled
model reefs (horizontal lined bars), painted filled model reefs (solid bars)
and hollow model reefs (hollow bars) off Palm Beach, Florida, U.S.A.
during the time period from September 1991 through December 1993.
Asterisks denote significantly greater and the dashes denote significantly
less than the fertilized filled reefs. N=3 model reefs for each treatment.
Figure 10. Mean number of fish by reef treatment on a log scale for the most
abundant species or species groups observed on model reefs off Palm
Beach, Florida, U.S.A. from September 1991 through December 1993:
Haemulon aurolineatum (torntate), H. spp. (unidentified grunts, newly
settled), Carangidae Oacks), Balistes capriscus (gray triggerfish),
Thalassoma bifasciatum (bluehead wrasse), Lutfanus griseus (gray
snapper), H. album and H. parra (margate and sailors choice combined), .
Anisotremus virginicus (porkfish), Pomacentrus spp. (damselfishes),
Acanthurus spp. (doctorfishes), L. synagris (lane snapper), Diplodus
holbrooki (spottail pinfish), Abudefduf saxatilis (sergeant major), Equetus
spp. (drums). Asterisks denote significantly greater and dashes denote
49 significantly less than the fertilized filled reefs.
Figure 11. Model reefs in 9 in of water, 500 in off the coast of Palm Beach, Florida,
U.S.A. A) Painted reef replicate in September 1994, three years after reef
deployment and treatment with anti4ouling paint. B) Reef replicate that
was not painted with anti-fouling paint.
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