ELSEVIER Journal of Experimental Marine Biology and Ecology

lSl(1994) 105-115

JOURNAL OF EXPERIMENTAL MARINE BlOLOQY AND ECOLOGY

Influence of colour of substratum on recruitment of spirorbid tubeworms to different types of intertidal boulders

R. J. James*, A. J. Underwood

Received 29 September 1993; revision received 22 February 1994: accepted 25 March 1994

Abstract

Spirorbid poiychaetes recruited to bare, dark grey shale boulders in greater numbers than to bare, light yellow sandstone boulders on the same shore. We examined the influence of colour on recruitment. Manipulative field experiments showed that: (1) more spirorbids recruited to dark- coloured boulders than to light-coloured boulders regardless of the type of rock; (2) the colour of the top of the boulder made little difference to the number of spirorbids recruiting to the undersurface of the boulders; and (3) more spirorbids recruited to shale boulders with dark- coloured undersurfaces than to those with light-coloured undersurfaces regardless of the colour of the top of the boulders. These results highlight the importance of colour as a physical factor affecting the recruitment of spirorbids to initially bare boulders. The colour of boulders did not, however, explain the magnitude of differences in recruitment to sandstone and shale boulders; other physical factors such as surface texture of the boulders may be important. Biological inter- actions such as the ‘*gregariousness” of spirorbids may amplify initial patterns of recruitment in the short-term but shortages of space may cause spirorbids to recruit to initially unfavourable habitats.

Keywords: Differential recruitment; Intertidal boulders; Rock type; Sandstone; Shale; Spirorbids

1. Introduction

Recruitment can be an important process in determining the patterns of distribution and abundance of marine invertebrates (e.g. Denley & Underwood, 1979; Yoshioka, 1982; Gaines et al., 1985). Many factors influence patterns of recruitment. At large

* Corresponding author. Present address: Graduate School of the Environment. Macquarie University,

NSW 2109, Australia.

OO22-0951/94/$7.00 0 1994 Elsevier Science B.V. All rights reserved

SSDI 0022-098 1(94)00060-Q

106 R.J. James. A.J. Underwood 1 J. E.xp. Mar. Biol. Ecol. 181 (1994) 105-115

scales, recruitment is affected by hydrodynamic processes that control the dispersal of

planktonic larvae (see references in Gaines et al., 1985). At smaller scales, biological

interactions such as pre-emptive competition (Kent & Day, 1983; Underwood & Denley, 1984) and facilitation (Gallagher et al., 1983) and physical factors such as micro-habitat diversity, composition of the habitat (McGuinness & Underwood, 1986) and the dis- tribution of larvae in the water column (Grosberg, 1982; Gaines et al., 1985) can all affect recruitment.

The type of rock making up intertidal shores has received attention as a potential influence on the recruitment of barnacles to rock platforms (e.g. Catfey, 1982; Raimondi, 1988) and of organisms to intertidal boulders (McGuinness & Underwood, 1986). The causes of any observed patterns of differential recruitment to different types of rock may be hard to pinpoint because there are many characteristics, including micro-habitats, chemical composition, colour, roughness and friability of the surface that vary among types of rock. Further, for boulders composed of different types of rock there may also be differences in shape and thickness. The possible interactions between these physi- cal characteristics mean that properly controlled experimental manipulations are re- quired to assess the causes of differential recruitment to different types of rock.

Spirorbid tubeworms are sedentary, tubicolous polychaetes and one of the initial colonizers of the undersides of intertidal boulders on shores around Sydney (McGuinness, 1988). McGuinness & Underwood (1986) found significantly more

spirorbids recruited to initially bare shale boulders rather than to initially bare sand- stone boulders after 86 days in the intertidal zone (recruitment here is defined as settlement, metamorphosis and survival until counted by an observer; Underwood, 1979). The importance of differential patterns of recruitment of sessile marine inver- tebrates to different substrata is that they may account for the adult distribution de- spite post-recruitment mortality (e.g. Denley & Underwood, 1979; Yoshioka, 1982).

Many laboratory studies have examined patterns of settlement of spirorbid larvae on different substrata. Under laboratory conditions, settling spirorbid larvae are able to

respond to light, gravity (De Silva, 1962) chemical extracts from algae (Williams, 1964; Gee, 1965) microbial films (Knight-Jones, 1951; Crisp & Ryland, 1960; Meadows & Williams, 1963; Kirchman et al., 1982) and the presence of established spirorbids (Knight-Jones, 1951). They are also able to settle relatively quickly after hatching and

some species forego a pelagic phase if they are released onto a favourable substratum (Gee 1963; Al-Ogily, 1985). Despite the lack of independent replication and appropriate controls in many of these studies, it is clear that spirorbid larvae do not settle at ran-

dom over different substrata presented under laboratory conditions. They are able to select and settle on the substrata on which they naturally occur. The difficulties of applying the results of laboratory experiments to natural conditions are well known (see

Connell, 1974) and will not be discussed here. The objective of the present study was to determine the causes of the differential

pattern of recruitment of spirorbids to bare shale and sandstone boulders observed by McGuinness & Underwood (1986). We examined the effect of the obviously different physical structure of shale and sandstone boulders. Shale is dark grey in colour, made up of very fine particles and smooth to touch. Sandstone is a light yellow colour and consists of relatively large grains of sand (Z 1 mm diameter) cemented together.

R.J. James. A.J. Underwood/J. Exp. Mar. Biol. Ecol. 181 (1994) 105-115 107

Manipulative field experiments were used to examine the influence of colour on the recruitment of spirorbids to these different substrata.

2. Materials and methods

All experiments were done in the mid to low intertidal zone of a boulder field at the

Long Reef Aquatic Reserve, z 10 km north of Sydney, Australia (see McGuinness & Underwood, 1986 for description). The boulders used were obtained from above the high-water mark on various shores. All sandstone boulders were obtained from Cape Banks Scientific Marine Research Area and shale boulders from Long Reef and other

shores nearby. There were two criteria used to select boulders. First, since we wanted to study

recruitment to initially bare boulders, those that were free of living or dead macro-

organisms were used. It is unlikely that marine micro-organisms would have been present on the boulders since they were obtained from high-levels on the shore. The second criterion for collecting boulders was size. It was desirable to use large boulders

to minimize loss and disturbance but we needed boulders that were small enough to enable their manipulation and transport. All boulders had a naturally flattened profile (McGuinness 1987) and a surface area of between about 400 and 1200 cm2 on their

upper and lower surfaces. These boulders measured about 30 to 50 cm along their longest axis.

Boulders were identified in the field by plastic tags glued to their upper and lower

surfaces using Selleys HydrEpoxy 501 waterproof glue. The glue and tags did not appear to have any effect on the distribution of sessile organisms on the boulders. For sampling, the position of each quadrat was randomly chosen from a 5 x 5 cm grid temporarily placed on the surface of each boulder. Randomly-chosen quadrats that included the tag were rejected and another position was chosen at random.

Different species of spirorbid are difficult to distinguish in the field because of their small size. Previous studies have shown that Janun pseudocorruguta (Bush) and Pileolaria pseudomilitaris (Thiriot-Quievreux) are the two most abundant species of spirorbid on intertidal boulders in the Sydney area (Knight-Jones et al., 1974) and in

the Long Reef boulder field (McGuinness & Underwood, 1986). In this study, all

species of spirorbid were considered together.

2.1. A4anipulation.s of the colour of boulders

We experimentally tested the hypothesis that the colour of shale and sandstone boulders influences the number of spirorbids that recruit to them. The colour of sand-

stone and shale boulders was changed to dark grey and light yellow, respectively, by painting them with one coat of “paving” paint (Beger Jet Dry) which did not notice- ably change the surface texture of the boulders. For each type of rock (shale and sandstone), three experimental boulders (sandstone painted dark grey and shale painted light yellow) plus three control boulders (sandstone painted light yellow and shale painted dark grey) and three natural boulders (not painted) were placed within three,

108 R.J. James, A.J. Underwood/J. E.xp. Mw. Biol. Ecol. 181 (1994) 105-I 15

5 x 5 m sites chosen ad hoc at about the same level in the mid to low intertidal zone

of the boulder field. Spirorbids were counted in four, 5 x 5 cm quadrats on the under-

surface of each boulder 74 days after the experiment was started (start 16.4.1988).

Such an experiment could be analysed by a 4-factor analysis of covariance using the size of the boulder as the covariate. The mean density of spirorbid recruits, however, did not covary with the surface area of natural shale and sandstone boulders in a previous experiment (over all samples, after 85 days: r = -0.40, 16 df, p> 0.05; after 113 days: Y = -0.18, 16 df, p> 0.05). Further, because two or three boulders of different sizes were randomly assigned to each type of rock, treatment and site in the present studies, any effect of the size of the boulders on recruitment would be randomly dis- tributed among these sources of variation. Analyses of variance were used here.

2.2. Mffiz~~ulat~o~z~ of the colours of the top and bottoms of boulders

The first experiment demonstrated marked differences in the recruitment of spiror- bids to light- and dark-coloured boulders (see Results). Spirorbids are, however, only found on the undersurfaces of boulders where light is reduced and colour is an unlikely cue. Accordingly, a second experiment was done to examine the colour of the top of boulders (which would be visible or might, through reflectance, influence the settling of larvae) and the bottom of boulders as separate potential influences on recruitment.

Due to the large number of treatments required for this experiment (nine in all), only shale boulders were used. The top (including the sides) and the bottom of each boul- der was treated as an experimental (painted light yellow), control (painted dark grey) or natural (not painted) surface. Each combination of these treatments was used. Two boulders from each combination of treatments were placed in each of three, 5 x 5 m sites chosen ad hoc at about the same level within the mid to low intertidal zone of the boulder field. Spirorbids were sampled using four 5 x 5 cm quadrats per boulder 78 days

after the start of the experiment (start 23.7.1988).

3. Results

3.1. Manipulations of the colour of boulders

The abundance of spirorbid recruits varied among treatments in a different fashion for each type of rock (significant type by treatment interaction, Table 1). There also were significant differences in the number of spirorbid recruits among sites and among boulders within each combination of type of rock, treatment and site (Table 1). Where terms that were tested against Boulders(Ty x Tr x S) were not significant at p>O.25,

they were pooled to provide more powerful tests (Winer et al., 1991; see Table 1). Natural or experimentally painted dark boulders received more recruits than natu-

ral or experimentally painted light-coloured boulders regardless of the type of rock (Fig. 1). As a result, there were significantly more spirorbids on the experimentally dark-co~oured sandstone boulders than on the light-co~oured natural and control sand- stone boulders which had similar numbers of recruits (SNK test on means for sand-

R.J. James, A.J. Underwood/J. Exp. Mar. Biol. Erol. 181 (1994) 105-115 109

Table 1

Analysis of the abundance of spirorbids on the undersides of shale and sandstone boulders after 74 days

Source df MS F F vs. pooled p p vs. pooled

Type of rock = Ty 1 9100.0

Treatment = Tr 2 311.5

Site = S 2 5226.3 11.59 10.001 TyxTr 2 6524.0 14.47 <O.OOl

Ty x S 2 743.3 1.53 > 0.20

TrxS* 4 280.7 0.58 > 0.65

TyxTrxS* 4 318.4 0.66 > 0.60

Boulders(Ty x Tr x S)* 36 484.6 5.89 <O.OOl

Residual 162 82.3

Pooled* 44 451.0

Sandstone and shale boulders (i.e. type of rock) were unpainted, painted their own colour (controls) or

painted the colour of the other type of rock (experimental). Three replicate boulders of each type and

treatment were placed in each of three sites. Type of rock and treatment were fixed factors whereas site and

boulders were random factors. Data were not transformed (Cochran’s test, p>O.O5). * Indicates pooled

components of the analysis (see text). In this and Table 2, F-ratios for main effects involved in significant

interactions are not given because tests of these main effects are meaningless (Underwood, 1981).

stone in Fig. 1, ~~0.05). Also, the experimentally light-coloured shale boulders had significantly fewer recruits than the natural and control shale boulders which had similar

numbers of recruits (SNK test on means for shale in Fig. 1, ~~0.05). Because there was no significant difference between the number of spirorbids that recruited to the

control and natural boulders, there is no reason to suspect that painting the boulders has influenced this experiment.

There were no significant interactions between treatments and sites, nor types of rock and sites and thus patterns of recruitment were consistent across the three sites. The differences in the number of spirorbid recruits among sites presumably reflect spatial

Shale Sandstone

Fig. 1. Mean ( + SE; n = 36 quadrats, 4 on 9 boulders) number of spirorbid recruits (per 25 cm’ after 74 days) on shale and sandstone boulders from each of three treatments. Solid black= natural boulders, stippled =control boulders (shale painted dark grey, sandstone painted light yellow) and diagonal lines = experimental boulders (shale painted light yellow, sandstone painted dark grey).

110 R.J. James, A.J. Underwood/J. Exp. Mar. Biol. Ecol. 181/1994) 105-115

variability in intensity of recruitment and are not considered further. Significant vari-

ation in the abundance of spirorbids among replicate boulders (those nested within the same type of rock, treatment and site) indicates that, although the relative abundance

of recruiting spirorbids varied significantly due to the colour of the boulders, the ab- solute abundance of recruits is likely to vary among boulders over a spatial scale smaller than metres.

There were significant differences from site to site in the effects on recruitment of the

different painting treatments on the tops and bottoms of boulders (T x S and B x S were significant in Table 2). There were, however, no significant interactions between the treatment of the top and the bottom of the boulders. So, whatever differences occurred on boulders with different treatments to their undersurfaces, the differences were the same whatever the treatment to the top of the boulder (and vice versa). Consequently, to compare treatments to the tops of boulders, data from all boulders treated the same could be averaged (Fig. 2). There were no significant differences in recruitment to the undersurfaces of boulders with tops treated differently (SNK tests on means for each site in Fig. 2, p > 0.05 for all comparisons).

In contrast, boulders with undersurfaces treated di~erently had different abundances of recruits. Relatively large numbers of recruits were found on natural or control (i.e. painted dark grey) undersurfaces of boulders and very few were found where under- surfaces were painted light yellow (SNK tests, p < 0.05; this is obvious in Fig. 3). This result was consistent for all three sites. This was most easily interpreted as no consistent

Table 2 Analysis of the abundance of spirorbirds on bottoms of boulders with different treatments on tops and

bottoms

Source df MS F I’

Top of boulder =-I- 2 0.0740

Bottom of boulder = B 2 18.0309

Site = S 2 1.0313

TxB 4 0.1412 0.81 > 0.50

TxS 4 0.2548 2.92 < 0.05

BxS 4 0.5076 5.82 < 0.005

TxBxS 8 0.1739 1.99 >0.05

BouldersjT x B x S) 27 0.0872 2.60 to.001

Residual 162 0.0336

Top and bottom of boulder refer to the treatment of the tops and bottoms of the boulders, respectively. Only

shale boulders were used and the treatments were: natural boulders; control boulders (painted the colour of shale); experimental boulders (painted the colour of sandstone). Each combination of these treatments

was applied to the tops and bottoms of the boulders. Two replicate boulders with each combination of

treatments were placed in each of three sites. Top and bottom of boulder were fixed factors whereas site and

boulders were random factors. Data were collected 78 days after deploying the boulders and were trans-

formed to log,,(_x + 1) to stabilize variances (Cochran’s test, p> 0.05 after transformation).

R.J. James, A.J. Undenvcwd 1 J. Exp. Mar. Biol. Ecnl. 181 /1994j IOS-115 111

Site 1 Site 2 Site 3

Fig. 2. Mean ( + SE; IP = 24 quadrats, 4 on each of 2 boulders with upper surfaces of each of 3 treatments) number of spirorbids recruits (per 25 cm’ after 78 days) on the undersurfaces of shale boulders with upper surfaces subjected to different treatments. Solid black = natural, stippied = control (painted dark grey) and diagonal lines = experimental (painted light yellow) surface on the tops of shale boulders.

effect of the paint, but variation from site to site in the numbers of spirorbids referring to the two boulders sampled for each treatment.

The sites differed, however, in the patterns of recruitment to naturally dark versus

painted dark (control) surfaces. At Site I, there was no difference. At Site 2, there were more recruits on the control (painted) surfaces, but, at Site 3, there were more on the unpainted, natural surfaces (Fig. 3). This was most easily interpreted as no consistent effect of the paint, but variation among sites in the numbers of spirorbids settling on the two boulders sampled for each treatment,

Again, there were significant differences between the replicate boulders for each

combination of treatments and sites (Table 2), indicating significant small-scale vari- ation in recruitment.

25

Site 1 Site 2 Site 3

Fig. 3. Mean ( + SE; n = 24 quadrats, 4 on each of 2 boulders with undersurfaces of each of treatments) number of spirorbid recruits (per 25 cm* after 78 days) on undersurfaces of shale boulders with under- surfaces subjected to different treatments. Solid black = natural, stippled = control (painted dark grey) and diagonal lines = experimental (painted light yellow) surface on the bottoms of shale boulders.

II:! R.J. James. A.J. Underwood/J. Exp. Mar. Biol. Ecol. 181 (1994) 105-115

4. Discussion

A major determinant of the differential recruitment of spirorbid tubeworms to sand-

stone and shale boulders was the colour of the underside of the boulders. Natural or experimentally painted dark-coloured boulders had more recruits than natural or ex- perimentally painted light-coloured boulders, regardless of the type of rock. Further, the

colour of the bottom of shale boulders was found to affect recruitment regardless of the colour of the top of the boulders. More spirorbids recruited to shale boulders with natural dark-coloured undersurfaces than to shale boulders with light-coloured under- surfaces regardless of the colour of the top of the boulders.

There have been few other studies where the colour of the surface of different sub- strata has been shown to affect recruitment. A similar result was, however, reported by Wisely (1959) for two unidentified species of Spirorbis in Sydney Harbour that re- cruited in much greater numbers to black bakelite rather than to clear Perspex fouling plates after 28 days exposure of the plates. These results were confounded by the use of different substrata in addition to different coiours.

Avoidance of light-coloured substrata by spirorbids may be due to negative photo- tactive behaviour immediately before settlement. This is a common trait of the larvae of marine invertebrates living in undersurface environments (Buss, 1979). The recruit-

ment of spirorbids to shale boulders with dark-coloured undersurfaces in preference to shale boulders with light-coloured undersurfaces is problematic since the undersurfaces of boulders are shaded. The colour of the undersurface of the boulder may be impor- tant only in boulder fields where light is able to illuminate the bottoms of the boulders and where spirorbids recruit during daylight. In the present study, boulders were placed at the surface of the boulder field (i.e. on top of the many small boulders in the boul- der field) and were rarely surrounded by sediment. In the boulder field at Long Reef,

the amount of sediment between boulders varied over time (pers. obs.). In boulder fields with little sediment, the colour of the undersurface of the boulder may be more impor-

tant than in boulder fields where the boulders are surrounded by sand. It is, however, unlikely that the bottoms of bare boulders would be colonized by spirorbids if they were usually buried in sand and recruitment may only take place when the undersurfaces of

the boulders are exposed. Manipulations of the colour of boulders may, in theory, also have affected the

temperature of the boulders (i.e. confounding colour and temperature). Spirorbids only settle while the boulders are submersed when temperatures of the different types of rocks are likely to be similar. Differences in temperature regimes of shale and sandstone boulders may, however, affect recruitment via differential survival. The undersurfaces of boulders were always shaded and almost invariably damp during low tide. We consider that different temperatures of the boulders are unlikely to be responsible for the observed patterns.

Differences in the colour of shale and sandstone boulders explained much of the variation in recruitment of spirorbids between these two types of rock. There were, however, significantly fewer recruits on experimentally dark-coloured sandstone boul- ders than on natural shale boulders, indicating that other causes contribute to the differential patterns of recruitment of spirorbids to shale and sandstone boulders. These

R.J. James, A.J. Underwood/J. Exp. Mar. Biol. Ecol. 181 (1994) 105-115 113

presumably include factors such as texture of the surface and chemical composition of

the boulders. For example, Raimondi (1988) showed that recruitment of the intertidal barnacle Chthamalus anisopoma (Pilsbury) to granite (rough texture) was greater than to naturally smooth basalt on two shores.

Some spirorbids have been shown to respond to chemicals released by algae to which they attach (e.g. Williams, 1964; Gee, 1965), but it is unlikely that chemicals released from boulders are cues for settlement. Models explaining the differential recruitment of spirorbids to the different types of boulder in terms of the chemical composition of the

rock are superficially questioned by the experiments that included painted boulders. Responses to chemicals in boulders would probably be altered by paint on the boul- ders. Numbers of spirorbids recruiting to control shale boulders (painted dark grey)

were significantly different from those on natural shale boulders at two of the three sites in the second experiment. At one site, significantly more spirorbids recruited to con- trol boulders than to natural boulders whereas the opposite occurred in the other site. This demonstrates no consistent effect of paint and no obvious direct chemical influ- ence of the boulders themselves.

Biological interactions may affect the recruitment of spirorbids to boulders. McGuinness (1988) found that spirorbids more quickly recolonized areas cleared in patches of spirorbids or bryozoans rather than areas on bare boulders. This may be due to the “gregariousness” (Knight-Jones, 1951) of spirorbids or the ability of their

brooded larvae to settle almost immediately (Fauchald, 1983) and thus quickly recolo- nize free space near established adults. Such mechanisms could amplify initial patterns of differential recruitment. Shortages of space in favourable habitats may, however, lead

to the colonization of unfavourable habitats and the patterns detected in this study apply only to the initial recruitment of spirorbids to‘ bare boulders. It is not clear

whether, in the long term, sandstone boulders are worse habitats for spirorbids than

are shale boulders. Colonization of boulders by spirorbids may also be influenced by the bacterial or

algal films that develop on surfaces in the ocean (e.g. Kirchman et al., 1982; Mitchell, 1984). Kirchman et al., (1982) suggested that, although bacteria appear to be respon- sible for inducing metamorphosis of the spirorbid Janus brasiliensis (Grube), indi- vidual strains of bacteria vary in their capacity to induce settlement and metamor- phosis. Thus, differences in the recruitment of spirorbids to shale and sandstone boulders may be partly due to any differences in the type of bacterial assemblages developing on the initially bare boulders. Painting boulders should make their sur- faces somewhat hydrophobic and therefore more difficult for bacteria to attach (e.g.

Zobell, 1943). In most cases in the two experiments, natural and control boulders (painted their natural colour) had similar mean abundances of spirorbid recruits. This implies a lack of dependence of spirorbids on particular surface films or no difference in surface films between unpainted and painted boulders of the same type

of rock. Differences in the degree of disturbance may also affect populations of spirorbids on

shale and sandstone boulders. Shale boulders tend to be more flattened than sandstone boulders and may be more or less prone to disturbance (McGuinness, 1987). A sep- arate study revealed no differences in the distances moved by the different types of

114 R.J. James. A.J. Underwood/J. Exp. Mar. Biol. Ecol. 181 (1994) 105-115

boulders used in this study (unpubl. data). No boulders were found inverted or moved

from their nominal 5 x 5 m site during the present experiments.

Overall, this study has identified the impo~ance of colour as a physical character-

istic of bare boulders affecting the recruitment of intertidal spirorbid worms. The dif- ference shown was strongly influenced by the colour, rather than the composition of the rock. This does explain (largely) the original pattern of difference in recruitment between sandstone and shale shown by McGuinness and Underwood (1986). The difference in recruitment as a response to colour may have implications for other studies of fouling organisms, particularly where artificial substrata are used in experiments. Why colour affects the recruitment of spirorbids and how the larvae respond to different colours remain mysteries to be unravelled.

Acknowledgements

These preliminary experiments were supported by a grant from the Australian Research Council (to AJU) and funds from the Institute of Marine Ecology. We are grateful to K. McGuinness for advice, to C. and J. James for support and to A. and M. James for assistance with field-work.

References

Al-Ogily, S.M., 1985. Further experiments on larval behaviour of the tubicolous polychaete Spirorbk inornatus L’Hardy & Quihreux. J. Exp. Mar. Biol. Ecol., Vol. 86, pp. 285-298.

Buss, L.W., 1979. Habitat selection, directional growth and spatial refuges: why colonial animals have more

hiding places. In, Biology and sytemarics of coioniui organisms. edited by G. Larwood & B.R. Rosen.

Academic Press, New York, pp. 459-497.

Caffey, H.M., 1982. No effect of naturally-occurring rock types on settlement or survival in the intertidal

barnacle. Tesseropora rosea (Krauss). J. Exp. Mar. Biol. Ecol., Vol. 63, pp. 119-132.

Connell, J.H., 1974. Ecology: field experiments in marine ecology. In, Experimental marine biology, edited by

R. Mar&al, Academic Press, New York, pp. 21-54.

Crisp, D.J. & J.S. Ryland, 1960. InBuence of filming and of surface texture on the settlement of marine

organisms. Kature (Land.). Vol. 185, pp. 119. Denley, E.J. & A.J. Underwood, 1979. Experiments on factors influencing settlement, survival and growth

of two species of barnacles in New South Wales. J. Exp. Mar. Biol. Ecol., Vol. 36, pp. 269-293.

De Silva, P.H.D.H., 1962. Experiments on choice of substrata by Spirorbis larvae (Serpulidae). J. Exp. Biol., Vol. 39. pp. 483-490.

Fauchald, K., 1983. Life diagram patterns in benthic polychaetes. Proc. Biol. Sot. Waafh.. Vol. 96, pp. 160-

177.

Gaines, S., S. Brown &J. Roughgarden. 1985. Spatial variation in larval concentrations as a cause of spatial

variation in settlement for the barnacle Balanus glandula. Oecologia (Berlin), Vol. 61, pp. 267-212. Gallagher, ED., P.A. Jumars, D.D. Trueblood, 1983. Facilitation of soft-bottom benthic succession by tube

builders. Ecologr. Vol. 64. pp. 1200-1216.

Gee, J.M., 1963. Pelagic life of .Spirorbis larvae. Nature (London), Vol. 198, pp. 1109-l 110. Gee, J.M., 1965. Chemical stimulation of settlement in larvae of Spirorhis rupesfris (Serpulidae). A&z. Behav.,

Vol. 13, pp. 181-186. Grosberg, R.K., 1982. Intertidal zonation of barnacles: the influence of planktonic zonation of larvae on

vertical distribution of adults. Ecology, Vol. 63, pp. 894-899.

R.J. James. A.J. Underwood/J. E-up. Mar. Biol. Ecol. 181 (1994) 105-115 115

Kent, AC. & R.W. Day, 1983. Population dynamics of an infaunal polychaete: the effect of predators and

an adult-recruit interaction. J. Exp. Mar. Biol. Ecol.. Vol. 73, pp. 185-203.

Kirchman. D.. S. Graham, D. Reish & R. Mitchell, 1982. Bacteria induce settlement and metamorphosis

of Janua (De.yiospira) brasiliensis Grube (Polychaeta: Spirorbidae). J. Exp. Mar. Biol. Ecol.. Vol. 56,

pp. 153-163.

Knight-Jones, E.W., 195 1. Gregariousness and some other aspects of the settling behaviour of Spiro&k. J.

Mar. Biol. Assoc. U.K., Vol. 30, pp. 201-222.

Knight-Jones, E.W., P. Knight-Jones & L.C. Llewellyn, 1974. Spirorbinae (Polychaeta: Serpulidae) from

southeastern Australia. Notes on their taxonomy, ecology, and distribution. Rec. Aust. Mu.. Vol. 29,

pp. 107-151.

McGuinness, K.A., 1987. Disturbance and organisms on boulders. 1. Patterns in the environment and the

community. Oecologia (Berlin), Vol. 71, pp. 409-419.

McGuinness. K.A., 1988. Short-term effects of sessile organisms on colonization of intertidal boulders. J.

E.xp. Mar. Biol. Ecol., Vol. 116. pp. 159-175.

McGuinness. K.A. & A.J. Underwood, 1986. Habitat structure and the nature of communities on intertidal

boulders. J. Exp. Mar. Biol. Ecol., Vol. 104. pp. 97-123.

Meadows. P.S. & G.B. Williams, 1963. Settlement of Spirorbis borealis Daudin larvae on surfaces bearing

films of micro-organisms. Nature (London), Vol. 198, pp. 610-611.

Mitchell. R., 1984. Colonization by higher organisms. In, Microbial adhesion and aggregation. edited by K.C.

Marshall, Springer-Verlag. Berlin, pp. 189-200.

Raimondi, P.T., 1988. Rock type affects settlement, recruitment, and zonation of the barnacle Chthamahrs

anisopomu Pilsbury. J. Exp. Mar. Biol. Ecol., Vol. 123, pp. 253-267.

Underwood, A.J. 1979. The ecology of intertidal gastropods. Adv. Mar. Biol., Vol. 16, pp. 11 l-210.

Underwood. A.J. 198 1. Techniques of analysis of variance in experimental marine biology and ecology.

Oceanogr. Mar. Biol. Annu. Rev., Vol. 19, pp. 513-605.

Underwood, A.J. & E.J. Denley, 1984. Paradigms, explanations, and generalizations in models for the

structure of intertidal communities on rocky shores. In, Ecological communities: conceptual issues and the

evidence, edited by D.R. Strong, D. Simberloff, L.G. Abele & A.B. Thistle. Princeton University Press,

Princeton, pp. 15 l-180.

Williams, G.B.. 1964. The effect of extracts of Fucus serrutus in promoting the settlement of larvae of Spirorbis

bore& (Polychaeta). J. Mar. Biol. Assoc. U.K., Vol. 44, pp. 397-414.

Winer, B.J.. D.R. Brown & K.M. Michels, 1991. Sratisficulprinciples in experimental design. McGraw-Hill,

New York, third edition, 1057 pp.

Wisely, B., 1959. Factors influencing the settling of the principal marine fouling organisms in Sydney

Harbour. Aust. J. Mar. Freshwater Res., Vol. 10, pp. 30-44.

Yoshioka, P.M., 1982. Role of planktonic and benthic factors in the population dynamics of the bryozoan

Membranipora membrunacea. Ecology, Vol. 63, pp. 457-468.

Zobell. C.E.. 1943. The effect of solid surfaces upon bacterial activity. J. Bacr.. Vol. 45, pp. 39-56.