Recruitment and community development of sessile fouling assemblages on the continental shelf off South Carolina, U.S.A.

Estuarine,

Coastal

and Shelf

Science

(1988) 26,679-699

Recruitment and Community Development of Sessile Fouling Assemblages on the Continental South Carolina, U.S.A.

Robert F. Van Dolah, Priscilla Knott and Elizabeth L. Wenner

H. Wendt,

Marine Resources Research Institute, South Carolina Resources Department, P.O. Box 12559, Charleston, U.S.A. Received

13 February

1987 and in revised

Keywords: fouling; recruitment; South Carolina Coast

form

community;

Shelf

David

off

M.

Wildlife and Marine South Carolina 29412,

17 December

1987

development;

continental

shelf;

The development of fouling communities was studied by deploying arrays of formica-covered Plexiglas plates in sand- and hard-bottom habitats on the continental shelf off South Carolina. Effects of season, substratum orientation, length of exposure, and proximity to natural hard-bottom habitat were evaluated over a one-year period with respect to the recruitment and community development of epibenthic organisms. Results indicate that the composition of sessile communities initially colonizing the plates was influenced more by season than by orientation or proximity to the hard bottom. Effects of orientation were related to predation, which appeared to be greatest on the upper surfaces of horizontal plates. Community development was initially similar in both habitats; however, after one year colonial species were dominant on plates locatedover hard bottom and solitary species were dominant on plates located over sand bottom. The eventual differences noted in species composition indicated that proximity to hard-bottom habitat may have a major influence on sessile communities developing on newly exposed hard surfaces.

Introduction The colonization and community development of hard substrata in shallow marine environments have been the subject of numerous investigations (for reviews, see Woods Hole Oceanographic Institution, 1952; Connell, 1972; Menge & Sutherland, 1976; Osman, 1977; Sebens, 1986). Studies in deeper-water environments, however, have been much more limited (e.g. Aleem, 1958; Fager, 1971; Dayton, 1975; Jackson, 1976, 1977; Neushul et al., 1976; Witman, 1985). This lack of information is especially evident in the South Atlantic Bight region, where hard-bottom habitats form a significant portion of the continental shelf (Miller & Richards, 1980; Parker et al., 1983). Although recent studies have examined the composition of benthic communities in these habitats (Continental 679 0272-7714,'88/060679+21

$03.00/O

@ 1988 Academic Press Limited

680

R. F. Van Dolah et al.

6. 6.4 cm $1~ angle IrOn 01 IO x 20

tt Figure

4.0

1. Diagram

of the fouling

n-l

cm sleet

I-beam

I

plate frame.

Shelf Associates, 1979; Wenner et al., 1983, 1984), little is known about their early development (Peckol, 1980; Williams et al., 1984). This paper presentsresults from an experimental study of sessilefouling biota colonizing artificial substrata in middle shelf depths off South Carolina. The objectives of this study were to (1) identify seasonalrecruitment patterns in both sand-bottom and hard-bottom environments, and (2) evaluate the effects of season,substratum orientation, and proximity to natural hard-bottom habitat on the early development of epibenthic communities. Methods Field and laboratory

Two large steel frames with arrays of fouling plates (Figure 1) were deployed off the South Carolina coast in March 1983. One frame was placed over hard bottom approximately 35 km south-east of Charleston, SC. This area was characterized by low-relief rock outcroppings and extensive areasof hardpan covered by a thin layer of sand [seePowles and Barans (1980) for a more detailed description]. The other frame was placed on sand bottom approximately 16 km south-west of the hard-bottom site. Water depths were equivalent (approximately 20 m) at both sitesand each areawas initially surveyed using an underwater television camera system to document the surrounding bottom type. These surveys confirmed that extensive hard-bottom habitat completely surrounded the frame placed over hard bottom; no hard bottom was observed within several kilometers of the sand-bottom site. The frames were anchored from two sidesand acoustic pingers were attached to aid in their relocation. Each frame supported 40 fouling plates oriented in alternating vertical and horizontal rows, with adjacent rows staggered to diminish effects from shading and disruption of currents (Figure 1). Although the plates on each frame were in close proximity to eachother, this designassumedthat eachplate functioned independently asa receptor site for settling organisms since it was not feasible to separatethe plates on truly independent structures located in multiple hard- and sand-bottom sites. All plates measured20 x 25 cm and were constructed of two sheetsof black, textured formica with a

Senile

fouling

March

1983

June

681

1983

September October

1983

December

March

assemblages

I983

1984

Figure 2. Schedule of deployment (shaded boxes) and retrieval (open boxes) of plates from frames located in the sand-bottom and hard-bottom areas. Numbers depicted in each block indicate the number of plates deployed and retrieved as well as the length of exposure.

&mm Plexiglas sheet sandwiched between them. Pilot studies by Schoener and Schoener (1981) indicated that textured formica was a very suitable material for fouling studies. Five replicate plates were randomly selected from each of four treatment groups for retrieval at 3-, 6-, 9- and 12-month intervals following the date of deployment. Two treatment groups represented plates in vertical and horizontal orientations over sand bottom, and the other two represented the same orientations over hard bottom (Figure 2). Prior to retrieval, divers fastened Plexiglas boxes (each encompassing an area of 225 cm’) to both sides of each plate in order to capture associated motile epifauna and protect the sessile growth from damage during the retrieval process. Aboard the research vessel, all sessile fauna not encompassed by the Plexiglas boxes were scraped from the plates, which were then preserved separately in 107, formalin in seawater with each plate surface tagged. An additional series of 10 new plates (five horizontal, five vertical) were attached to each frame during the 3-, 6-, and 9-month site visits to evaluate seasonal recruitment. These plates were collected after a 3-month exposure to provide four sets of plates submerged for equivalent periods during the different seasons (Figure 2). The plates were removed from the frame using the technique described above. In the laboratory, three of the five replicate plates from each treatment group were randomly selected for analysis. The remaining plates were used only to replace damaged plates in a treatment group. Sessile biota within the central 22%cm2 area of plate surfaces were identified to the lowest possible taxonomic level and estimates of percentage cover were obtained for all species using a random point-count censusing technique similar to that described by Sutherland and Karlson (1977). Each census was accomplished by submerging the plate in water and overlaying it with a transparent acetate sheet marked

682

R. F. VanDoluhet al.

with 100 random points. One of three sheetswith different arrays of random points was randomly selectedfor the analysis of eachplate treatment group. All points were examined under a binocular microscope and the identity of any organism(s) or the occurrence of a bare spot wasnoted. Dead barnacles(empty tests) were alsonoted, but their coverage was not included in the tabular estimates of barnacle coverage. Percentage cover estimates were computed by dividing the number of points under which a speciesoccurred by the total number of points evaluated on eachplate ( x 100). As more than one speciesoccurred under many points, the sum of the percentage cover estimates for all specieson each surface frequently exceeeded lOO:b. The number of points examined in this censuswas basedon a preliminary analysiswhich indicated that a minimum of 100points was needed to estimate cover accurately for all specieswhich occupied at least 59$ of the plate surface (South Carolina Wildlife and Marine ResourcesDepartment [SCWMRD], 1984). After completion of the point-count census, plates were scraped and the total wet weight biomass on each plate surface was measured. Separate biomass measurements were also obtained for the following categories: actiniaria, algae, ascidiacea, cirripedia, hydroidea, mollusca, polychaeta, and porifera. Treatment of motile fauna associatedwith the plates is described elsewhere(SCWMRD, 1984). Data analysis Total percentage cover, total biomass, and number of species per plate surface were compared with respect to plate side, orientation, location and seasonor duration of submergence. Statistical comparisons of variates between plate sides (top US.bottom, ‘pinger’ side VS. ‘opposite’ side to define vertical plate sides) were made using t-tests, or the approximate t-test when variances were heterogeneous (Sokal & Rohlf, 1981). Comparisons of variates between plates orientations (horizontal vs. vertical), plate locations (hard bottom vs. sand bottom) and among seasonsor durations of plate submergence were completed using three-way (Model I) analysis of variance (Sokal & Rohlf, 1981). Basedon preliminary evaluations of data normality and heterogeneity of variance, t-tests and analysesof variance were computed using the arcsin transformation for percentage cover estimates, the log,, transformation for species number, and no transformation on biomassdata. The a posteriori Ryan-Einot-Gabriel-Welsh multiple F test (Ramsey, 1978) was then used to determine significant differences between treatment group means. The level of significance for all statistical tests was a = 0.05. Cluster analyses were performed to determine patterns of similarity in community structure among the different plate series. Data were compared using the Bray-Curtis similarity coefficient (Bray & Curtis, 1957) based on percentage cover estimates. Data setssubjected to cluster analysis were first reduced to eliminate very rare specieswhich occurred on only one replicate set of plates and had lessthan 591~cover on those plates. Species and collections were classified using flexible sorting with a cluster intensity coefficient (p) of -0.25 (Lance & Williams, 1967). Normal classifications were produced for the data set representing plates submerged for 3 months during different seasons,and for the data set representing plates submerged for 3,6,9 and 12 months. Results

and discussion

Seasonalrecruitment Recruitment and initial growth of fouling organisms on the plates was extensive during all seasons,with the average percentage cover of sessilebiota on the plates submerged for

Sessilefouling

assemblages

683

3-month periods generally exceeding 70” 0 (Table I). On all plates, numerous small organisms formed the biotic cover, rather than any one organism dominating the plate surface. Cover was significantly lower on plates submerged during the spring than on those exposed during other seasons(Table 2), but the average cover on any surface was never lessthan 42”,, . No significant differences in percentage cover existed between plates over sand-bottom and plates over hard-bottom or between horizontal and vertical plates. A significant interaction was noted, however, between the factors of location and season (Table 2). This wasprimarily due to a much greater difference in cover observed between locations during spring but not during the other seasons.There were no significant differences in percentage cover between the sidesof the vertical plates from either frame; however, biota cover was significantly less on the top of horizontal plates than on the bottom in four of the eight treatment groups (Table 3). Comparisons of the number of specieson the 3-month plates in relation to season, location, and surface orientation showed highly significant seasonaldifferences, with a greater number of speciesper plate observed in the hard-bottom than in the sand-bottom area (Table 2). No significant differences werenoted between horizontal and vertical plates (Table 2) or, withone exception, between plate sideshaving the sameorientation (Table 3). Total biomasson the plates after 3-month submergencewas greatest during winter and lowest during spring and summer in both locations (Table 1). As noted for percentage cover and speciesnumber, seasonaldifferences in plate biomasswere highly significant (Table 2). Analysis of variance of biomasson the plates indicated no significant differences related to the main effects of plate location or orientation. However, significant interactions were noted between seasonand the factors of plate location and orientation (Table 2), suggesting that proximity to hard bottom and surface orientation play a role in influencing seasonalrecruitment and growth. Differences in biomassbetween plate sides were not significant for vertical plates, but were significant for five of the eight horizontal plate series(Table 3). This was probably the result of differential settlement patterns and predation effects on top US.bottom surfaces,as will be discussedlater. Taxa forming the predominant cover on the plates during all seasonswere barnaclesand hydroids (Table l), with barnacles accounting for more than 90”,, of all biomassscraped from the plate surfaces. Two species,Balanus venustus and B. trigonus, were commonly observed during the spring, summer, and fall. Baianusvenustus wasalways more abundant than B. trigonus on plates from both areas,and it wasthe only barnacle speciesobserved on plates submerged during the winter. The amount of barnacle cover was similar among plates collected from both frames during summer, fall, and winter (Table 1). Greatest barnacle cover was present on the plates exposed during fall and winter, with immature specimensoften observed growing on larger barnacles, both living and dead. The percentage cover of living barnacles was lower on the top surfaces compared to bottom and vertical surfaces during all seasons except winter. Hydroid cover wasgenerally greatest during the spring and summer and lowest during the winter on plates from both sand-bottom and hard-bottom areas(Table 1). The two speciesmost commonly observered were Obelia dichotoma and Clytia fragilis. Halocordyle disticha was also abundant on sand-bottom plates during the summer and fall (Table 1). Coverage by Obelia dichotoma was usually greater than that by C. fragilis on all plate surfaces, and both speciesformed a low mat of growth on the barnacle tests and bare surfaces. Halocordyle disticha growth, on the other hand, was often much higher and grew in discrete clumps.

biota cover biomass (g wet wt) number of species

Total Total Total

89 61 7

1

53 55

42 16 8

22 3 4

Spring

1

P, pinger;

90 113 2

89

98 119 3

1

97 1

Winter

0, opposite;

88 79 8

15

14

41 1 23

77 17 9

55 13 2 2

70 41 6


37 47 1

Fall

(T)

13 21 2 6

80 33 6

2

9 30 5 5

Surnmer

Horizontal

100 92 8


27

92 29 8 2

100 78 6

19

93 66 6

Fall

(B)

H, hydroid;

94 47 6

13 38
58 6 4 22

99 47 8

6

50 60 36 33 28

Summer

Ba, barnacle;

77 54 5


42 57 3

87 52 6

34 20 48 tl 10

Spring

Horizontal

96 41 7

5 5 2

47 29 38 23

96 35 7

76 62 1 1 6

Summer

Al, algae.

77 49 5

42 57 4

72 30 6

31 9

24 19

Spring

As, ascidian;

100 125 2

100

99 127 5


99
Winter

Vertical

1

1

1 96 79 9

cl

90 32 3 1

98 93 7


96 38 5

Fall

(P)

1. Estimates of mean percentage cover, biomass, and total number of sessile species which were on the plates submerged for three months during the spring, summer, fall and winter seasons

T, top; B, bottom;

biota cover biomass (g wet wt) number of species

Sand-bottom platform Balanus venustus (Ba) Obelia dichotoma (H) Balanus trigonus (Ba) CZytiu frugiZis (H) Symplegma viride (As) Halocordyle disticha (H) Turritopsis nutriculu (H) Ceramium strictum (Al)

Total Total Total

Hard-bottom platform BaZunus venusrus (Ba) Obelia dichotoma (H) Balanus trigonus (Ba) Clytia fragilis (H) Symplegma vi&e (As) Halocordyle disticha (H) Turritopsis nutricula (H) Ceramium strictum (Al)

examined

TABLE

95 119 2

95

95 137 3

1

95

Winter

observed

86 55 4

42 57 4

70 25 6

18 41 7

18

Spring

under

93 41 7

7 30
49 17 35 15

94 38 6

53 65 5 1 9

Summer

Vertical

at least

98 87 8


90 44 7 1

99 100 8

23 7

96 24 1

Fall

(0)

94 112 2

93

97 133 2

96

Winter

1 Y,, of all points

Sessile fouling

assemblages

685

TABLE 2. Results of three-way analyses of variance (Model I) comparing percentage cover, number of species, and biomass of sessile biota on horizontal and vertical plates exposed for 3 months during different seasons and in different locations

Source

Degrees of freedom

of variation

Deperzdent Model (r’ Factor A: Factor B: Factor C: Interaction AxB AXC BxC ArBxC

variable: arcsin = 0.50) platform location season of exposure surface orientation effects

percentage

Dependent Model (r’ Factor A: Factor B: Factor C: Interaction AxB AxC BxC AxBxC

variable: loglo (No. =0.77) platform location season of exposure surface orientation effects

Dependent Model (r’ Factor A: Factor B: Factor C: Interaction AxB .I x c BxC AxBxC

variable: biomass (g wet wtj =O-86) platform location season of exposure surface orientation effects

cover/plate 15 1 3 1

F

5.27’ 0.00 NS 20.79’ 1.18NS

3 1 3 3

2.90” 0.11 NS 1,67NS 0.56 NS

15 1 3 1

17.99’ 4.02” 80.16’ 2.34 NS

3 1 3 3

5.52b 0.00 NS 1.59NS 0.58 NS

15 1 3 1

31.72’ 0.04 NS 139.34’ 0.13 NS

3 1 3 3

8.07’ 0.22 NS 3.97b 7.10’

Results of aposteriori comparisons (REGW

I&<

testY’

PS”7 Pm, kv,

species/plate)

NS, Not significant. “Significant at 0.05 level. %ignificant at 0.01 level. Significant at 0.001 level. ‘Ryan-Einot-Gabriel-Welsh multiple significantly different at a = O-05.

F test; means connected

by underlines

are not

Hydroid cover on plates submerged during the spring was lower in the hard-bottom than in the sand-bottom area (Table 1); however, this difference was not observed during other seasons. One hydroid species, Turritopsis nutricula, was only present during summer, and it was most abundant in the sand-bottom area. Hydroids were rare or absent on the plates during winter, with only a few stalks of hydroids belonging to the family Tubulariidae being present. No consistent patterns were noted in the distribution of hydroids on the different plate surfaces from either frame. The only other taxa which covered more than l’$c, of the 3-month plates were the ascidian Symplegma z&de, and the alga Ceramium strictum (Table 1). Symplegma &ride formed thin sheetsovergrowing barnaclesand bare surfacesand wasmost common on the underside of horizontal plates over hard bottom. No ascidianswere observed on the top

Horizontal Vertical Horizontal Vertical

bottom bottom bottom bottom

bottom bottom bottom bottom

bottom bottom bottom bottom

bottom bottom bottom bottom

Hard Hard Sand Sand

Hard Hard Sand Sand

Hard Hard Sand Sand

Hard Hard Sand Sand

ND, no difference between “Significant at 0.05 level. %gnificant at 0.01 level. ‘Significant at 0.001 level.

Horizontal Vertical Horizontal Vertical

Horizontal Vertical Horizontal Vertical

Horizontal Vertical Horizontal Vertical

Plate orientation

Plate location

means;

PT
30.73’ 0.08 4.17b 1.16 0.75 0.82 3.93” 0.35

NS NS NS NS

pT;SpB

NS NS

NS

pT
kNSPT

%ipB

I? rank

cover

number

1.98 0.09 3.31 0.52

ts

Percentage

biota cover, seasons

2.93” 0.69 2.85” 2.00

NS, not significant.

Winter Winter Winter Winter

Fall Fall Fall Fall

Summer Summer Summer Summer

Spring Spring Spring Spring

Season of submergence

3. Results of c-test comparisons oftotal percentage sides of plates exposed for 3 months during the different

TABLE

0.63 1.49 ND ND

0.36 1.22 1.29 0.29

0.67 0.62 3.00” 1.01

1.17 ND 1.26 1.88

ts

of species,

NS NS NS NS

NS NS NS NS

NS NS PB
NS NS NS NS

Sz rank

No. species

and biomass

1.12 0.42 1.48 0.71

3.92” 0.61 2.10 2.16

13.26 0.39 6.36* 0.12

3.04# 1.15 2.94” 0.67

ts

Biomass

(g wet wt) of sessile biota attached

NS NS NS NS

PT
PT
PT’PB NS PB
X rank

to opposite

Sessile fouling assemblages

-0% i -0,4

-I

-0.2 !

0 2 ; 0

0.2-

E G

1 0.4

SFXJSOfl

w

Orlentatlon

OPOTPBBTBOPOP8,BPOTOPT/OPTTTOPBBBT

Plate

s s H H H H s S/HH H s s SIS 5 s H H H S/HH HIti sls s H H s s

locat ion

Group

w

www

w

w

WIF

F

F

F

F

F ~sPsPsPFsususP~sPsPsP~susuJsusususus”F

I

I

I

I

12

I

I

I

I 3

I

I

I

14151 I

I

6 I

Figure 3. Dendrogram resulting from normal analysis of percentage cover estimates of sessile species attached to plates submerged for three months during the different seasons. S, sand-bottom area; H, hard-bottom area; T, horizontal top surface; B, horizontal bottom surface; I’, pinger; 0, opposite.

surfacesof 3-month plates. Ceramium strictum is a finely branched red alga that was most abundant on the tops of horizontal plates during summer and fall in the sand-bottom area. This speciesand other algaewere also found on the vertical plates, but rarely grew on the underside of horizontal plates. Cluster analysis of the 3-month plates, based on percentage cover estimates of the various speciespresent, resulted in distinct groupings related to the seasonof plate submergence (Figure 3). Plates deployed during the winter formed Group 1, exhibiting very high similarity among plate surfacesregardlessof location or orientation. The high similarity among these plates was due to the almost complete cover by Balanus venustus on all plate surfaces. Six of the eight plate seriesdeployed during the fall formed Group 2, which

688

R. F. Vun Dolah et al.

alsohad relatively high similarity among entities due to heavy coverage by B. venustus and Obelia dichotoma. Cluster Group 3 included all plates deployed on sand bottom during spring, and most of the vertical hard-bottom plates deployed during summer. This group was relatively dissimilar to Groups 1 and 2 and to Groups 4-6. The latter three groups contained the other spring and summer plates from both frames, with someseparation by surface orientation, season,and location, Evaluation of all community parameters on the 3-month plate seriesindicated that the seasonof exposure had a greater influence on the community composition of sessilebiota colonizing hard substrata in the study area than did surface orientation or location. Sutherland (1974) and Sutherland and Karlson (1977) also noted seasonaldifferences in early fouling communities asthey developed on plates submerged in shallower waters of North Carolina. They suggested that these differences can influence subsequent community development, resulting in multiple stable end-points dependent on when community development began. Seasonalvariations in speciesrecruitment in their study area, however, were much greater than we observed, especially with respect to the morphology of early colonizers. In our study, barnaclesand hydroids, which covered the plates with a low ‘mat-like’ growth, were the dominant taxa noted during all seasonsexcept winter, when hydroid growth was reduced. Thus, subsequent community development (after 3 months) on hard substrata exposed during different seasonsmight be more similar in shelf waters off South Carolina than was noted by Sutherland (1974). However, this hypothesis remains untested becausethe 3-month plates were only intended to provide data on seasonalrecruitment and early community development patterns. Few of the dominant speciesobserved on the 3-month plates are major components of early developing communities in shallower waters. Balanus venustus and B. trigonus, for example, were the only barnacles present on the plates in this study, with B. venustus covering most of the primary spaceon all plate surfaces. Although both specieshave a worldwide distribution (Zullo, 1979), neither specieshas been reported asthe dominant barnacle covering hard surfaces in shallower (l-2 m) subtidal waters of the south-eastern United States(Mook, 1976,198O;Van Dolah et al., 1984; WHOI, 1952)or in deeperwaters of such other regions asthe Gulf of Mexico (George &Thomas, 1979;Fotheringham, 1981; Gallaway et al., 1981) or the Pacific (WHOI, 1952;Aleem, 1958;Davis et al., 1982). Zullo (1979) noted that B. venustus is the most common subtidal barnacle of the Virginian province and that reproductive populations of B. trigonus are restricted to the region south of Cape Hatteras, North Carolina. Williams et al. (1984) recently described the population biology of B. trigonus in shelf waters off North Carolina, but relatively little is known about differences in the distribution and life history patterns of these two species. On our 3month plates, B. venustus showed lessseasonalvariability in abundance than did someof the other species,although there were more B. venustus on the plates during fall and winter than during spring and summer. Balanus trigonus, on the other hand, was more common on the 3-month plates during spring and summer and was rare or absent on the plates during the fall and winter. Werner (1967) suggestedthat B. trigonus is relatively intolerant of cooler temperatures, which may account for the lack of B. trigonus spat on plates submerged during the winter. Cooler temperatures did not, however, result in substantial mortality of this speciessince many large B. trigonus were observed on the 12-month plates exposed during winter (seebelow). Williams et al. (1984) alsonoted this specieson tiles immersed from December to April. Most of the hydroids growing on the 3-months plates have been collected from other areas of the northwestern Atlantic (Fraser, 1944). The most prevalent species, ObeZiu

Sessilefouling assemblages

689

dichotoma, has been commonly observed in shallower waters of South Carolina (Calder et al., 1977a,b; Zingmark, 1978; Van Dolah et al., 1979,1984). Several investigators have noted that Obelia spp. are early colonizers on hard surfacesin both shallow and deep water

(Aleem, 1958; Fager, 1971; Greene & Schoener, 1982; Vandermeulen & DeWreede, 1982). Once established, colonies of 0. dichotoma can inhibit settlement of barnacle larvae (Standing, 1976). Thus, the reduced coverage of this hydroid and others which had similar morphologies (Clytia frugilis, Turritopsis nutricula) during the cooler months may account for the higher percentage coverage of barnacles on the plates exposed during winter. Aside from these seasonaldifferences, there were no consistent differences in total hydroid cover with respect to surface orientation or proximity to hard bottom. Effects of surface orientation were most obvious with respect to algal, ascidian, and barnacle growth. The greater cover of algaeon top plate surfacesis similar to algal growth patterns noted by Vandermeulen and DeWreede (1982), and is probably related to the availability of light. Ascidians, on the other hand, were restricted to the bottoms of horizontal plates and to vertical plate surfaces. This may reflect a preferential settling on surfaces which are shaded and lessprone to sedimentation, predation, and competition from algaeasnoted by Young and Chia (1984). Predation also may have affected the distribution of speciesobserved on the plates. Evidence of predation on barnacles wasgreatest on the tops of horizontal surfaces, which had significantly lower total biotic cover and biomassthan was observed on the underside of horizontal plates. Filefish, sheepshead,spadefish, black sea bass, and blennies were present around both fouling plate frames, and all of these species were occasionally observed grazing on the plates. Furthermore, diets of the latter three speciesare known to include barnacles and ascidians (Gallaway et al., 1981; SCWMRD, 1984). Harris and Irons (1982) also found that predation was greater on the tops of horizontal surfacesand suggestedthat predation and siltation are the primary factors influencing communities on those surfaces. Proximity to hard-bottom habitat did not appear to have a significant influence on the total percentage cover or biomasson the 3-month plates, but there were significant differences between habitats in the number of speciessettling on those plates. The greater number of speciespresent on plates placed in the hard-bottom area probably reflects a greater pool of larvae from sessilespeciesgrowing nearby, especially those having larvae which settle quickly. For example, ascidians were much more common on plates in the hard-bottom than in the sand-bottom area. This agreeswell with observations by Berrill (1950), Olson (1985), and Young (1986), who noted that tadpole larvae of many ascidians are only in the water column for a few minutes to a few hours. Thus, fewer ascidian larvae might be expected to reach the sand-bottom plates becausemost of the speciesobserved in this study are restricted to hard-bottom habitats.

Community

development

Biotic cover increased significantly with time on the 3-, 6-, 9- and 12-month plate series (Tables 4 and 5). After 9 months, the average coverage on plates from both frames exceeded 950
biota cover 6) biomass (g wet wt) number species (?i)

Total Total Total

“For

abbreviations

see Table

89 61 7

1.

8 20

55
78 61 9

1

4 46
6 4

53

81 67 8

2

6

42 16 8

9 11

1 26

3

95 103 11

5 1 7 28 39 1

4 4

95 157 16

32

1

38 36 21 2 7

39 19

(6,onth,9,

(T)

22 4

3

Horizontal

90 149 15

41

36

5 5

99 215 17

27

18

15

25 16 35 1

12

77 54 5

42 3 3 57

87 52 6

34 48 10 20
3

85 66 7

6 1

10 45
30 21

98 246 7


25

25 83 31

(6,onth~

Horizontal

99 151 10

3 20 20 64 1 28 1

38 23

100 400 11

6 4 8

17 75 76 3 1 7 41

(B)

4. Estimates of the mean percentage cover, biomass, and total number on the plates submerged for 3,6,9, and 12 months”

biota cover 62) biomass (g wet wt) number of species (Z)

Sand-bottom platform Balanus venustus (Ba) Balanus trigonus (Ba) Symplegma viride (As) Obelia dichotoma (H) Clytiafragihs (H) Styelaplicata (As) Halocordyle disticha (H) Ceramium strictum (Al) Hydractiniidae A (H) Turritopsis nutricula (H) Distaplia bermudensis (As) Champia parvula (Al)

Total Total Total

Hard-bottom platform Balanus venustus (Ba) Balanus ttigonus (Ba) Symplegma viride (As) Obelia dichotoma (H) Clytiafragilis (H) Styela plicata (As) Halocordyle disticha (H) Ceramium strictum (Al) Hydractiniidae A (H) Turritopsis nutricula (H) Distaplia bermudensis (As) Champia parvula (Al)

examined

TABLE

3

100 349 9


1 13 75

14 5

100 468 12

15 1 32

14 34 45 7 14 8

12

77 49 5

57

42 4

72 30 6

31

24 19 9

3

88 61 7

7

28 15 <1 34

35 6

99 187 10


11

3

23 71 59 16 10 2

98 98 11


20 8 20 16 9 7 56 9 17 2

100 346 17

7 2 3

6

24 77 71 11 4 6

(P)

96 206 13

13 2

22 9 6 3 7 53

100 433 14


2

17 36 61 1 10 10

12

were observed

~mo*th,9,

Vertical

of sessile species which

86 55 4

61

42 4

70 25 6

41

18 18 7

3

under

88 55 7

13

28 13
39 14

98 219 9

16
3

33 68 63 12 4
Vertical

97 100 12

55 13 4 24 4 4 43 1 11 <1 1

100 307 11

3 5


27 76 77 4 18 4

(0)

97 270 9

3

5 63

43 7

100 469 9


14 12

17 49 76

12

at least 1% of all points

Sessile fouling

assemblages

691

TABLE 5. Results of three-way analyses of variance (Model I) comparing percentage cover, number of species, and biomass of sessile biota on horizontal and vertical plates exposed for 3-, 6-, 9- and 12-month intervals in different locations

Source

Degrees of freedom

of variation

Depertdent Model (r’ Factor A: Factor B:

variable: arcsin \//percentage = 0.73) platform location time of exposure

cover/plate 15 1 3

variable: log,, (No. species/plate) = 0.66) platform location time of exposure

variable: biomass = 0.77) platform location time of exposure

Factor C: surface orientation Interaction effects AxB AxC BxC AxBxC

test)

14.78’ 6.13 59.58’

8.76b 1.30 NS 1.35 NS 0.41 NS

Factor C: surface orientation Interaction effects AxB AxC BxC AxBxC Deperrdent Model (r* Factor A: Factor B:

Results of a posteriori comparisons (REGW

3.90’

Factor C: surface orientation Interaction effects AxB ArC BxC AxBxC Dependem Model (r’ Factor A: Factor B:

F

15 1 3

10.31b 13,01b 43,66b

1

0.64 NS

3 1 3 3

0.22 NS 0.14 NS 1.84 NS 1.22NS

(g wet wt) 15 1 3

17.49b 44.75b 6 1.08*

1

2.12 NS

3 1 3 3

8.44* 2.88 NS 0.99 NS 0.39 NS

NS, Not significant. “Ryan-Einot-Gabriel-Welsh multiple significantly different at a = 0.05. ‘Significant at 0.001 level. “Significant at 0.05 level.

F test; means

connected

by underlines

are not

cover between vertical and horizontal plates, but the a posterior-i test indicated that this difference was negligible (Table 5). The percentage cover was generally highest on the bottom and lowest on the top of horizontal plates but, with a few exceptions, the differences werenot significant (Table 6). There were no significant differences in the amount of biotic cover on different sides of the vertical plates. The average number of species on the plates increased significantly with duration of submergence (Tables 4 and 5). After 9 months, the number of species on plates from both the sand-bottom and hard-bottom locations approached or exceeded the number on 12months plates. There were also significantly more species on the hard-bottom plates than on the sand-bottom plates during every sampling period (Table 5). Effects of plate

9 9 9 9 12 12 12 12

Horizontal Vertical Horizontal Vertical

Horizontal Vertical Horizontal Vertical

bottom bottom bottom bottom

bottom bottom bottom bottom

Hard Hard Sand Sand

Hard Hard Sand Sand

1s

1.00 1 .oo 2.59 0.15

2.53 1.00 1.17 0.86

4.61b 0.78 1.31 1.28

2.93” 0.69 2+35” 2.00

NS, not significant.

6 6 6 6

Horizontal Vertical Horizontal Vertical

bottom bottom bottom bottom

Hard Hard Sand Sand

means;

3 3 3 3

Horizontal Vertical Horizontal Vertical

bottom bottom bottom bottom

Hard Hard Sand Sand

ND, no difference between “Significant at 0.05 level. bSignificant at 0.01 level.

Duration of submergence (months)

Plate orientation

Plate location

number

NS NS NS NS

NS NS NS NS

P(T
)1T
T rank

cover

biota cover,

Percentage

6. Results of t-test comparisons of total percentage sides of plates exposed for 3,6,9 and 12 months

TABLE

1.94b 4.38 1.91 4.13b

2.36 3.96” 0.38 0.48

1.94 0.97 2.79 0.45

1.17 ND 1.26 1.88

ts

of species,

3.06” 0.67 3.17” 0.11

4.43b 0.57 6.20b 0.12

4.07* 0.75 O-98 0.62

3.04” 1.15 2.94” 0.67

ts

Biomass

(g wet wt) of sessile biota attached

NS Po
NS Po
NS NS NS NS

NS NS NS NS

X rank

No. species

and biomass

k
PT
PT
k
X rank

to opposite

Sessile fouling assemblages

693

orientation on species number, however, were generally not significant, although some differences were noted between sides of the vertical plates after 9- and 12-months exposure (Table 6). Biomass increased with time in the 3-, 6-, 9-, and 12-month plate series,especially on the hard-bottom plates (Table 4). Differences in biomassrelated to submergencetime and area were highly significant; however, there was significant interaction between these main effects (Table 5). No consistent differences were noted in the total biomass on vertical versus horizontal plates (Table 5), but on horizontal plates there was usually significantly greater biomasspresent on the bottom sides(Table 6). No major differences were noted between sidesof vertical plates. Barnacles alone accounted for more than 95”,, of the total biomasson 3- and 6-month plates. On the 9- and 12-month plates, barnacles and ascidiansrepresented 99O, of the biomass. As noted previously, barnacles and hydroids accounted for the greatest percentage cover on the 3-month plates deployed in March. These taxa were also dominant on all plate surfacessubmerged for 6 months in the sand-bottom area, except for the top surfaces of horizontal plates, which had a slightly higher algal cover (Table 4). Clytiu frugilis and 0. dichotoma were the most common hydroids, although Halocordyle disticha was also present. Balanus venustus wasthe dominant barnacle species(by percentage cover) on the 6-month sand-bottom plates. In contrast, B. trigonus was the dominant barnacle on most 6-month plates collected from the hard-bottom area(Table 4). Only the top surfacesof the 6-month horizontal plates from the hard-bottom area had greater cover by B. venustus than by B. trigonus. Ascidian cover wasalsogreater on the 6-month hard-bottom plates than on the 3-month hard-bottom plates collected during the same season,or on the 6-month sand-bottom plates (Tables 1 and 4). Symplegma viride accounted for most of the ascidian cover on the hard-bottom plates, although Distaplia sp. A, D. bermudensis, and Styelaplicata were also present (Table 4). Ascidians were absent from the top of 6-month horizontal plates in the hard-bottom area, and accounted for lessthan 1O0of the biota cover on all surfacesof the sand-bottom plates. Species forming the primary cover on the 6-month plates in both locations were also common on the 9-month plates, which supported a total of 45 and 33 speciesin the hardand sand-bottom areas,respectively. Plates exposed for 9 months in the hard-bottom area had much greater ascidian cover than did either the 6-month hard-bottom plates or the 9month sand-bottom plates, which had greater hydroid cover (Table 4). Symplegma viride was the dominant ascidian on the hard-bottom plates, covering more than 70n,, of the vertical and horizontal-bottom surfaces. This speciesand two others (S. plicata and D. bermudensis) were also common on the sand-bottom plates. Hydroid cover was dominated by Hulocordyle disticha, especially in the sand-bottom area (Table 4). Barnacles and algaewere major components of the sessilecommunities on the 9-month plates in both areas(Table 4). Balanus venustus was the dominant barnacle in the sandbottom area, whereas B. trigonus was dominant on the plates in the hard-bottom area. As noted on the 3- and 6-month plates, algal cover was greatest on the tops of horizontal 9month plates. Dominant algal speciesin the hard-bottom area were Ceramium stricturn and Champia parvula, but only C. strictum was common on sand-bottom plates. Plates submerged for 12 months supported the most diverse fouling communities, with a total of 45 speciesobserved on plates from the hard-bottom area and 39 speciesobserved on plates in the sand-bottom area. Ascidians covered most of the plate surfaces,especially in the hard-bottom area where Symplegma viride and Distaplia bermudensis overgrew and

694

R. F. Van DoZuh et al.

smothered many of the barnacles. In contrast, Styelaplicata wasthe dominant ascidian on sand-bottom plates, which supported very little S. viride growth and no D. bermudensis. Hydroid cover was generally reduced on the 12-month plates with no living H. disticha observed in either area. Clytia fragilis, Monostaechas quadridens, and Hydractiniidae A were observed on all plates except in the sand-bottom area, where M. quadridens was rarely observed. The alga Ceramium strictum wasalsoan important component of the fouling community on the tops of horizontal plates submerged for 12 months (Table 4). Fourteen other algal specieswere observed on the plates, but only Champia parvula, Lomentaria baileyana and Polysiphonia denudata exceeded 10% cover on any plate surface. Other sessiletaxa observed on the plates included bryozoans, sponges, anemones, serpulid worms, and molluscs; however, no speciesrepresenting these taxa were observed under more than 10% of the points on a plate surface. Cluster analysisof the sessilecommunities on the 3-, 6- 9- and 12-month plates resulted in separation of plate surfaces by location and, to a lesserextent, by length of exposure and orientation (Figure 4). Groups l-4 contained all the sand-bottom plates except one, and the remaining two groups were formed by plates from the hard-bottom area. Among the four groups containing sand-bottom plates, greater dissimilarity in community composition wasnoted between plates exposed for different periods of time than between surface orientations. One exception to this pattern was Group 2, which showed a high similarity in the speciescomposition found on top surfacesof horizontal plates exposed for 6,9, and 12 months. Group 1 included 3-month plates, Group 3 included the 12-month plates, and Group 4 included the 6- and 9-month plates. In comparison to plates from the sand-bottom area, plate surfacesfrom the hard-bottom area showed greater similarity in fauna1 composition among the 6-, 9-, and 12-month exposure periods. Top surfaces, however, were relatively dissimilar to the other surfacessubmerged for the sameperiod of time. Top surfaces from all exposure periods formed Group 5, which also contained the other 3-month plate surfaces. In general, community development on the plates submerged during the spring appeared to be rapid, with significant changesin community structure occurring over the l-year period. There were also major differences in community structure between plates from the sand-bottom and hard-bottom areas.Initially, the dominant fouling organisms in both areaswere barnacles and hydroids, but barnacles occupied most of the primary surface area. By the end of the 12-month study period, the percentage cover of solitary specieson the plates had declined in the hard-bottom area and the dominant taxa were colonial ascidiansand hydroids. Many of the ascidianscompetitively excluded barnacles through overgrowth. In contrast, the dominant taxa covering plates in the sand-bottom area were solitary ascidiansand barnacles, and cluster analysis indicated major differences in the overall speciescomposition on plates from the two areas. Jackson (1977) suggestedthat colonial organismsare competitively superior to solitary forms inhabiting marine hard-substratum environments, and concluded that they can exclude solitary fauna when spaceis limited. Schoener (1982) and Greene and Schoener (1982), on the other hand, found that solitary organismseventually becamedominant over colonial forms. Results of our study indicate that colonial organismsbecome dominant in hard-bottom areas, while solitary organisms eventually dominate in sand-bottom areas. Therefore, we suggestthat proximity to hard-bottom habitat (areasproviding a sourcefor larval recruitment) has a major influence on the sessilecommunities developing on newly exposed hard surfaces.

Sessile fouling

695

assemblages

-7

- I.0

1

-o-a-

-0.6-

0.4-

0.6 -

0.8-

:xposure I period (months) Orlenfotlon Plate loCotlOn Group

‘12/3141

5

I

6

Figure 4. Dendrogram resulting from normal cluster analysis of percentage cover estimates of sessile species attached to the plates submerged for 3,6,9, and 12 months. Plate locations are identified as: S, sand-bottom area; H, hard-bottom area. Plate surface orientations are identified as: T, top; B, bottom; P, pinger; 0, opposite.

Sutherland (1974, 1978) also observed that both solitary and colonial organisms can dominate sessile communities. He suggested that stable points in community composition and structure are influenced by the species initially colonizing an area. Thus, seasonal differences in the species composition of early fouling assemblages on Sutherland’s plates played a major role in later community development. Conversely, Mook (1981) conducted similar studies in shallow waters of Florida and concluded that differences in the early fouling assemblages had little effect on the composition of later communities. Because our study was not designed to examine the effects of seasonal recruitment on later community

696

R. F. Van Dolah et al.

development, it is uncertain which of these two models of succession is operating in the South Atlantic Bight. It is clear, however, that very diffierent communities can develop even when the dominant taxa of early community development are similar. Community development also appeared to be influenced by plate orientation, but only with respect to the tops of horizontal plates, Those surfaces supported a large percentage of algal cover on the older plate series, and overall community composition of the top surfaces was generally more similar between sampling periods than on the other plate surfaces. Evidence of greater predation on the top surfaces of 3-month horizontal plates suggests that predators may also be influencing community structure on the top of older plates. Harris and Irons (1982) also reported a higher incidence of predation on the top surfaces of fouling panels. Sessile communities observed on the 12-month plates probably did not represent a ‘climax”or stable end-point in the community development, even though the total percentage biota cover on plate surfaces approached 100°/, after 9 months and there were no significant differences between 9 - and 12-month plates with regard to average number of species per plate. Biomass, however, increased considerably throughout the year, and cluster analysis indicated that similarity in species composition on older (9- and 12month) plates was relatively low in both study areas. Dominant species on the plates also differed from those which dominated sessile communities on older artificial reefs located in the South Atlantic Bight which ranged in age from 3.5 to 10 years (Wendt et al., in press). The lack of any obvious stabilization in community structure within a l-year period agrees with findings obtained in shallower waters of South Carolina (Van Dolah et al., 1984), where substantial shifts occurred in the structure and composition of sessile communities developing on subtidal rocks over a 4-year period. Finally, it is interesting to note that none of the larger sponges, octocorals, or hard corals typically found in hard-bottom areas of the South Atlantic Bight (SCWMRD, 1982) were observed on our fouling plates during the l-year sampling period. These species may represent later colonizers of hard substrata because at least some of the octocorals and hard corals are found on older artificial reefs (Wendt et at., in press). Few studies have examined the colonization rates and growth of most sponge and coral species present in this region, but evidence from other studies in temperate waters indicates that reef corals and sponges may take several years to attain their large sizes (Grigg, 1974; Nicol & Reisman, 1976). The apparently low recruitment rates and slow growth of these organisms suggest that destruction of these communities through natural disturbance or man-induced activities may have long-term consequences. Acknowledgements

We wish to thank several people for their considerable assistancein this study. Field collections were completed with the help of C. B. O’Rourke, E. C. Roland, G. R. Sedberry, and the crews of the R/V Oregon and R/V Lady Lisa. M. V. Levisen and J. Pinckney assistedin the field and laboratory processing of the plates and F. L. Folsum was responsible for the construction of the frames and plates. N. B. Peacock and M. S. Lentz typed drafts of this report and K. Swanson prepared the figures. We also wish to thank C. K. Biernbaum. A. Fritz, J. Hyland, R. T. Paine, G. R. Sedberry, and J. Sutherland for their comments on earlier drafts of this manuscript. This study was supported under contract 14-12-0001-29185 with the Minerals Management Service. This is contribution No. 234 from the Marine ResourcesCenter.

Sessile fouling

assemblages

References Aleem, A. A. 1958 Succession of marine fouling organisms on test panels immersed in deep-water at LaJolla, California. Hydrobiologia 11,40-58. Berrill, N. J. 1950 The Tunicara. Johnson Reprint Corporation, New York. Branscomb, S. 1973. The effects of predation and competition on the distribution and abundance of the barnacles Balanus improvisus and Balanus eburneus in the Chesapeake Bay. Masters Thesis, University of Maryland, College Park, Md. Bray, J. R. & Curtis, J. T. 1957 An ordination of the upland forest communities of southern Wisconsin. Ecology

Monographs

27,325-349.

Calder, D. R., Bearden, C. M., Boothe Jr, B. B. & Tiner Jr, R. W. 1977a A reconnaisance of the macrobenthic communities, wetlands, and shellfish resources of Little River Inlet, North Carolina and South Carolina. Technical Report No. 17. South Carolina Marine Resources Center, Charleston, SC. Calder, D. R., Boothe Jr, B. B. & Maclin, M. S. 19776 A preliminary report on estuarine macrobenthos of the Edisto and Santee River systems, South Carolina. Technical Reporr No. 22. South Carolina Marine Resources Center, Charleston, SC. Connell, J. H. 1972 Community interactions on marine rocky intertidal shores. Annual Reviews in Ecological Systems

3,169-192.

Continental Shelf Associates 1979 South Atlantic hard bottom study. Contract AASSI-CT88-25. Prepared for Bureau of Land Management. Davis, N., Van Blaricom, G. R. &Dayton, I’. K. 1982 Man-made structures on marine sediments: effects on adjacent benthic communities. Marine Biology 70,295-303. Dayton, P. K. 1975 Experimental studies of algal canopy interactions in a sea otter dominated kelp community at Amchitka Island, Alaska. Fisheries Bulletin 73,230-237. Fager, E. W. 1971 Patterns in the development of a marine community. Limnology and Oceanography 16, 241-253. Fotheringham, N. 1981 Observations on the effects of oil field structures on their biotic environment: platform fouling community. In Environmental Effects of Offshore Oil Production (Middleditch, B. S., ed.). Plenum Publishing Corporation, New York, pp. 179-208. Fraser, C. M. 1944 Hydroids of the Atlantic Coast of North America. University of Toronto Press, Toronto. Gallaway, B. J., Martin, L. R., Howard, R. L., Boland, G. S. & Dennis, G. D. 1981 Effects on artificial reef and demersal fish and macrocrustacean communities. In Environmental Effects of Offshore Oil Production (Middleditch, B. S., ed.). Plenum Publishing Corporation, New York, pp. 237-299. George, R. V. &Thomas, I’. J. 1979 Biofouling community dynamics in Louisiana shelf oil platforms in the Gulf of Mexico. In The Offshore Ecology Investigation: Effects of Oil Drilling and Production in a Coastal Environment. (Ward C. H., Bender, M. E. & Reish, D. J., eds). Rice University Studies Vol. 65. William Marsh Rice University, Houston, TX, pp. 553-574. Greene, C. H. & Schoener, A. 1982 Succession on marine hard substrata: a fixed lottery. Oeceanologia 55, 289-297. Grigg, R. W. 1974 Growth rings: annual periodicity in two gorgonian corals. Ecology S&876-881. Harris, L. G. & Irons, K. I’. 1982 Substrate angle and predation as determinants in fouling community succession. In Artificial Substrates (Cairns J. J., ed.). Ann Arbor Science, Ann Arbor, Michigan, pp. 131-174. Jackson, J. B. C. 1976 Habitat area, colonization, and development of epibenthic community structure. In Biology of Benthic Organisms (Keegan, B. F., Ceidigh, I’. 0. & Boaden, I’. J. S., eds). Pergamon Press, Oxford, pp. 349-359. Jackson, J. B. C. 1977 Competition on marine hard substrata: the adaptive significance of solitary and colonial strategies. American Naturalist 111,743-767. Lance, G. N. & Williams, W. T. 1967 A general theory of classificatory sorting strategies. I. Hierarchical systems. Computing Journal 9,373-380. Menge, B. A. & Sutherland, J. I’. 1976 Species diversity gradients: synthesis of the roles of predation, competition and temporal heterogeneity. American Naturalist 110,351-369. Miller, G. C. & Richards, W. J. 1980 Reef fish habitat, fauna1 assemblages and factors determining distributions in the South Atlantic Bight. Proceedings of the Gulfof Caribbean Fisheries Institute 32,114130. Mook, D. H. 1976 Studies on fouling invertebrates in the Indian River. 1. Seasonality of settlement. Bulletin of Marine Science26,610-615. Mook, D. H. 1980 Seasonal variation in species composition of recently settled fouling communities along an environmental gradient in the Indian River lagoon, Florida. Estuarine and Coastal Marine Science 11, 573-581. Mook, D. H. 1981 Effects of disturbance and initial settlement on fouling community structure. Ecology 62, 522-526.

698

R. F. Van Dolah

et al.

Neushul, M., Foster, M. S., Coon, D. A., Woessner, J. W. & Harger, B. W. W. 1976 An in situ study of recruitment, growth and survival of subtidal marine algae: techniques and preliminary results. Journal of Phycology 12,397-408. Nicol, W. L. & Reisman, H. M. 1976 Ecology of the boring sponge (Cliona celata) at Gardiner’s Island, New York. Chesapeake Science 17,1-7. Olson, R. R. 1985 The consequences of short distance larval dispersal in a sessile marine invertebrate. Ecology 66,30-39. Osman, R. W. 1977 The establishment and development of a marine epifaunal community. Ecological Monographs 47,37-63. Parker, Jr, R. C., Colby, D. R. & Willis, T. 0. 1983 Estimated amount of reef habitat in the U.S. South Atlantic and Gulf of Mexico continental shelf. Bulletin of Marine Science 33,935-940. Peckol, P. 1980 Seasonal and spatial organization and development of a Carolina continental shelf community. Ph.D. Dissertation, Duke University, Durham, NC. Powles, H. & Barans, C. A. 1980 Groundfish monitoring in sponge-coral areas of the southeastern United States. Marine Fisheries Review 42,21-35. Ramsey, P. H. 1978 Power differences between pairwise multiple comparisons. Journal of the American Statistical Association 73,479-485. Schoener, A. 1982 Artificial substrates in marine environments. In Artificial Substrates (Cairns, Jr, J., ed.). Ann Arbor Science, Ann Arbor, Michigan, pp. l-22. Schoener, A. & Schoener, T. W. 1981 The dynamics of the species-area relation in marine fouling systems. 1. Biological correlates of changes in the species-area slope. American Naturalist 118, 339-360. Sebens, K. P. 1986 Spatial relationships among encrusting marine organisms in the New England subtidal zone. Ecological Monographs 56,73-76. Sokal, R. R. & Rohlf, F. J. 1981 Biometry, 2nd edition. W. H. Freeman and Co., San Francisco, CA. South Carolina Wildlife and Marine Resources Department (SCWMRD) 1982 South Atlantic OCS Area Living Marine Resources Study Year II. Vol. I. An Investigation of Live-bottom Habitats off South Carolina and Georgia. Final report prepared for Minerals Management Service under contract AA55 lCTl-18. South Carolina Wildlife and Marine Resources Department (SCWMRD) 1984 South Atlantic OCS Area Living Marine Resources Study. Phase III. Final report prepared for Minerals Management Service under contract 14-12-0001-29185. Standing, J. D. 1976 Fouling community structure; effects of the hydroid, Obelia dichotoma, on larval recruitment. In Coelenterate Ecology and Behaviour (Mackie, G. O., ed.). Plenum Press, New York, pp. 155-165. Sutherland, J. P. 1974 Multiple stable points in natural communities. American Naturalist 108, 859-873. Sutherland, J. P. 1978 Functional roles of Schizoporella and Styela in the fouling community at Beaufort, North Carolina. Ecology 59,257-264. Sutherland, J. P. & Karlson, R. H. 1977 Development and stability of the fouling community at Beaufort, North Carolina. Ecological Monographs 47,425-446. Vandermeulen, H. & DeWreede, R. E. 1982 The influence of orientation of an artificial substrate (Transite) on settlement of marine organisms. Ophelia 21,41-48. Van Dolah, R. F., Calder, D. R., Knott, D. M. & Maclin, M. S. 1979 Effects of dredging and unconfined disposal of dredged material on macrobenthic communities in Sewee Bay, South Carolina. Technical Report No. 39. South Carolina Marine Resources Center, Charleston, SC. Van Dolah, R. F., Knott, D. M. & Calder, D. R. 1984 Ecological effects of rubble weir jetty construction at Murrells Inlet, South Carolina. Vol. I: Colonization and community development on new jetties. Environmental Impact Research Project. Technical Report EL-84-4. U.S. Army, Corps of Engineers, Waterways Experiment Station. Wendt, P. H., Knott, D. M. & VanDolah, R. F. 1989 Community structureofthe sessile bistaon fiveartificial reefs of different ages. Bulletin of Marine Science 44, in press. Wenner, E. L., Knott, D. M., Van Dolah, R. F. & Burrell Jr, V. G. 1983 Invertebrate communities associated with hard bottom habitats in the South Atlantic Bight. Estuarine, Coastal and She&Science 17,143-158. Wenner, E. L., Hinde, P. Knott, D. M. &Van Dolah, R. F. 1984 A temporal and spatial study of invertebrate communities associated with hard-bottom habitats in the South Atlantic Bight. NOAA Technical Report NMFS 18. Werner, W. E. 1967 The distribution and ecology of the barnacle, Balanus trigonus. Bulletin of Marine Science 17,64-84. Williams, A. H., Sutherland, J. P. & Hooper, M. R. 1984 Population biology of Balanus trigonus on a subtidal rocky outcrop near Beaufort, North Carolina. Journal of the Elisha Mitchell Scientific Society 100, l-l 1. Witman, J. D. 1985 Refuges, biological disturbance, and rocky subtidal community structure in New England. Ecological Monographs S&421-445. Woods Hole Oceanographic Institution (WHOI) 1952 Marine Fouling and its Prevention. U.S. Naval Institute, Annapolis, Maryland.

Sessile fouling

assemblages

699

Young, C. M. & Chia, F. S. 1984 Microhabitat-associated variability in survival and growth of subtidal solitary ascidians during the first 21 days after settlement. Marim Biology 81,61-68. Young, C. M. 1986 Direct observations of field swimming behaviour in larvae of the colonial ascidian Ecteinascidia turbinata. Bulletin of Marine Science 39,279-289. Zingmark, R. G. (ed.) 1978 An Annotated Checklist of the Biota of the Coastal Zone of South Carolzno. University of South Carolina Press, Columbia, SC. Zullo, V. A. 1979 Marine flora and fauna of the northeastern United States. NOAA Technical Rrporr IL;ZIFS Circular 425. U.S. Government Printing Office, Washington, DC.