Community structure of soft sediment pool fishes in Moreton Bay, Australia

Journal of Fish Biology (2011) 78, 479–494

doi:10.1111/j.1095-8649.2010.02866.x, available online at wileyonlinelibrary.com

Community structure of soft sediment pool fishesin Moreton Bay, Australia

C. A. Chargulaf*†, K. A. Townsend‡ and I. R. Tibbetts*

*School of Biological Sciences, The University of Queensland, St Lucia, Queensland 4072,Australia and ‡Moreton Bay Research Station, The University of Queensland, Dunwich,

North Stradbroke Island, Queensland 4183, Australia

(Received 3 May 2010, Accepted 1 November 2010)

A survey of soft sediment tide pools was conducted to assess the occupation and assemblage of fisheson three different intertidal shores in Moreton Bay, Australia, between January and December 2009.Tide-pool volume ranged from 0·30 to 29·75 l and varied significantly between months and sites.A total of 1364 individuals representing 15 species and nine families of fishes were observed. AtDunwich, fish assemblages were dominated by the sand goby Favonigobius lentiginosus (89%) andwhiting, Sillago spp. (10%). At Manly, the gobies Favonigobius exquisitus (37%), Pseudogobiussp. (31%) and the blenny Omobranchus punctatus (19%) dominated the shores while at GodwinBeach, F. lentiginosus (15%), F. exquisitus (45%) and Sillago spp. (25%) were the most abundantspecies. The mean ± s.e. density of fishes ranged from 0·29 ± 0·13 to 5·04 ± 1·74 fishes l−1 andabundance of fish correlated with pool volume. Juveniles (75%) dominated assemblages suggestingthat soft sediment pools may act as nurseries. The persistent and recurrent fish assemblages found insoft sediment tide pools in Moreton Bay suggest that these shores are behaving more like a tropicalthan a temperate climate shore, as there was no significant difference of fish abundances betweenseasons. © 2011 The Authors

Journal of Fish Biology © 2011 The Fisheries Society of the British Isles

Key words: fish assemblages; Gobiidae; nursery; tide pools.

INTRODUCTION

Low-energy coastal and estuarine depositional shores are characterized by a smallslope and large tidal variations (Meager et al., 2005). The changing tides bringinfluxes of either terrestrial or marine predators and at low tide, nekton remain-ing on the shore is confined to small pools and channels that are often subjectto rapid changes in temperature, salinity and pH (Metaxas & Scheibling, 1993).Soft sediment pools, in particular, are structurally unstable (Reidenauer & Thistle,1981) and are typically formed by sting-ray Myliobatis tenuicaudatus Hector forag-ing activity (Thrush et al., 1994). Nonetheless, a number of organisms utilize thesepools and channels during low tide as they provide protection from desiccation,aquatic predators (Ritter, 2008), abundant food (Larkin et al., 2009) and potentially,conditions for enhanced development (Kruck et al., 2009).

†Author to whom correspondence should be addressed. Tel.: +61 7 3365 4333; email: [email protected]

479© 2011 The AuthorsJournal of Fish Biology © 2011 The Fisheries Society of the British Isles

480 C . A . C H A R G U L A F E T A L .

The abundance and distribution of fishes in rock pools is well known (Bennett& Griffiths, 1984; Willis & Roberts, 1996; Beckley, 2000; Almada & Faria, 2004;Castellanos-Galindo et al., 2005; Rummer et al., 2009); however, in soft sedimentpools assemblages have received little attention. Although the diversity of fishesoccupying soft sediment pools has been recorded (Crabtree & Dean, 1982; Crowley& Tibbetts, 1995; Able et al., 2005; Meager et al., 2005; Taylor et al., 2005; Krucket al., 2009), little is known of their abundance and distribution, especially in poolsnot associated with estuaries or salt marshes. This is surprising given that someevidence suggests that these pools may act as nursery habitats for commerciallyimportant species (Kwik & Tibbetts, 1999; Kruck et al., 2009).

Seasonal variations of abundance of fishes in rock pools have been documented intemperate (Griffiths, 2003a) and boreal environments (Moring, 1990) with seasonalpatterns largely being attributed either to the recruitment of juveniles (Arakaki &Tokeshi, 2006) or changes in the environment (Willis & Roberts, 1996). Although intropical regions, where environments are typically less variable and seasonal differ-ences in abundance have not been detected, the ratio of mature to juvenile individualscan vary throughout the year (Castellanos-Galindo et al., 2005). Juvenile recruitmentis a key variable in the dynamics of tide-pool fish communities, yet, it is the occupa-tion of such pools by residents that cause their long-term temporal stability (Barreiroset al., 2004).

Despite a few studies in south-eastern New South Wales (Griffiths, 2003a, b),there is a paucity of knowledge concerning Australian tide-pool fish communitiesin regard to the abundance and distribution of their members (Ford et al., 2004).Moreton Bay is a subtropical bay in south-east Queensland that has sheltered shoresdominated by mangroves, seagrass beds and sand- and mud-flats. The sand- and mud-flats contain numerous pools, on both hard and soft substrata, that serve as habitatsfor many fishes and migratory birds. Indeed the wetlands surrounding the bay areprotected under the Ramsar Agreement, which includes 110 000 ha of intertidalmudflats, marshes, sand-flats and mangroves (Chan & Dening, 2007). The bay isinfluenced by freshwater inputs from several river systems, including the Brisbane,Pine and Logan Rivers, and saltwater inputs from the Coral Sea.

This study describes the community and size structure of fishes inhabiting softsediment pools on tidal flats in Moreton Bay, a subtropical estuary. On the basis ofdata from rocky shore pools (Bennett & Griffiths, 1984) and limited data from softsediment pools (Meager et al., 2005), it is predicted that larger pools will supportlarger abundances of fishes than smaller pools and further that patterns of occu-pancy over the year will be more similar to tropical than temperate systems, in thatoccupation will be persistent rather than seasonal.

MATERIALS AND METHODS

The study was carried out at three sheltered intertidal shores at Moreton Bay, Queensland,Australia: Dunwich, Manly and Godwin Beach (Fig. 1). The sites consisted of sand andmuddy-sand substrata in which pools occur at low tide. Dunwich sand-flat extends c. 500 mfrom mean high tide (MHT) to the sub-tidal. Manly has a small sand-flat that extends c. 200m from MHT to the sub-tidal and contains small isolated patches of rock. Godwin Beachextends c. 400 m from MHT to the sub-tidal. All three sites are adjacent to urban envi-ronments and are fringed to seaward by patchy Zostera muelleri seagrass. Godwin Beachcontains sparse Avicennia marina mangroves on either side of the upper shore beach.

© 2011 The AuthorsJournal of Fish Biology © 2011 The Fisheries Society of the British Isles, Journal of Fish Biology 2011, 78, 479–494

C O M M U N I T Y S T RU C T U R E O F T I D E - P O O L F I S H E S 481

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Fig. 1. Map of Moreton Bay, Australia, showing sampling sites (D, Dunwich; M, Manly; GB, Godwin Beach).

To evaluate the physical features and fish communities of soft sediment tide pools, 10isolated tide pools at each site in the zone of resurgence were randomly sampled on a monthlybasis from January 2009 to December 2009. Pools were sampled at each location on con-secutive days 1 h prior to expected low tide. Due to the ephemeral nature of soft sedimenttide pools, different pools were sampled each month. Maximum tide-pool length and widthwere recorded (±1 cm) and mean depth was estimated from five random depth measure-ments throughout the pool (Meager et al., 2005). Assuming an elliptical shape, pool areameasurements were converted to volumetric estimates.

To census fish assemblages, pool dwelling fishes were anaesthetized using 10% clove oilin seawater solution (Griffiths, 2000) and fishes were collected using small dip-nets (1 mmmesh). Clove oil quantities were adjusted to pool size at c. 5 ml l−1. All fishes were identifiedto species and standard length (LS) was measured (±1·0 mm) using dial callipers (Mitutoyo;www.mitutoyo.co.jp). Small cryptobenthic fishes, such as the sand goby Favonigobius lentig-inosus (Richardson) and the muzzled blenny Omobranchus punctatus (Valenciennes), wereconsidered adults when LS ≥ 20 mm while larger fishes, such as whiting, Sillago spp., wereconsidered adults when LS ≥ 140 mm (Kendall & Gray, 2009). Fishes were returned tonearby uncontaminated pools once they had resumed normal locomotion.

A two-factor repeated measures ANOVA was used to test the effects of spatial (site)and temporal (month) variations on volume of the tide pools using PASW Statistics 18.0.0.(http://pasw.en.malavida.com). The repeated measures ANOVA test examines the variationbetween sites as well as the variation within sites across the different months. The two factors,site and month, were considered fixed. The fish assemblages of each pool were described usingmean abundance, calculated using the mean number of fish l−1. Species richness (RS) wascalculated to determine the number of fish species occupying tide pools at each site through-out the year. Shannon–Wiener diversity indices (H ′) were calculated to compare speciesdiversity, while the Pielou evenness index (J ′) (Pielou, 1966) was calculated to quantify the



equality in numbers between the three soft sediment tide-pool assemblages. RS, H ′ and J ′were used to reduce the complexity of the data so that they could be analysed by multivariatestatistics. The assemblages of the tide pools were also analysed using a two-factor repeatedmeasures ANOVA.

In order to test for seasonal changes in fish abundance, two random months were sampled ateach site for each season, summer, autumn, winter and spring. A two-factor repeated measuresANOVA was conducted to test for seasonal differences and variation within a season.

Tide-pool assemblages were also analysed using non-parametric permutational multivari-ate analysis of variance (PERMANOVA) undertaken using PERMANOVA + Version 1.0.2for Primer Version 6.1.12 (http://www.primer-e.com). These comparisons were based on thecalculation of Bray–Curtis similarity values on fourth root transformed data and the testsrelied on 9999 random permutations. Assemblages were then depicted using non-metric mul-tidimensional scaling (MDS) represented by two-dimensional plots. Stress values (s) of theMDS ordination are considered good when s < 0·1.

In order to estimate species richness sample-based rarefaction curves were used, whichrequire Monte-Carlo re-sampling of all pooled samples for each site (Gotelli & Colwell,2001). Calculating rarefaction curves and their associated 95% CI provides more accurate rep-resentation of species diversity by standardizing species richness to a comparable number ofindividuals (Gotelli & Colwell, 2001). Rarefaction curves were generated from the EstimateSVersion 8.2.0 community analysis software (http://viceroy.eeb.uconn.edu/estimates).

Spearman rank correlation (rs) tests were conducted using Prism Version 5.03 (http://www.graphpad.com/welcome.htm) to evaluate the relationship between fish abundance and poolvolume. A repeated one-way ANOVA was used to assess differences in temporal distributionof the most common species. Tukey’s post hoc tests were used to determine where significantdifferences occurred.

RESULTS

A total of 1364 individuals from 15 species and nine families were identified insoft substratum tide pools during the study (Table I). At Dunwich, the five speciescaught were dominated by F. lentiginosus, which accounted for 89% of the totalcatch. At Manly, the nine species caught were dominated by the gobies Favonigo-bius exquisitus Whitley and Pseudogobius sp., which together with O. punctatusaccounted for 87% of the catch. At Godwin Beach the 10 species caught were dom-inated by the gobies F. exquisitus, F. lentiginosus and the bridled goby Arenigobiusbifrenatus (Kner), which together with Sillago spp. accounted for 96% of the catch.Only juvenile Sillago spp. and the common silver belly Gerres subfasciatus Cuvieroccurred in pools at all three sites.

Individual soft sediment tide-pool volumes throughout the year ranged between0·30 and 29·75 l at Dunwich, 0·34 and 24·44 l at Manly and 0·53 and 11·99 lat Godwin Beach. Repeated measures ANOVA showed that pool volumes weresignificantly different between months and sites (Table II).

The mean ± s.e. number of fishes l−1 throughout the year was between 0·29 ± 0·13and 3·11 ± 1·09 fishes l−1 at Dunwich, 0·35 ± 0·08 and 5·04 ± 1·74 fishes l−1 atManly and 0·61 ± 0·14 and 1·81 ± 0·52 fishes l−1 at Godwin Beach [Fig. 2(a)]. Thehighest recorded mean number was at Manly in May while the lowest value wasfound at Dunwich in September. At each location, fishes were found occupying poolsevery month; however, some sampled pools contained no fishes. Mean ± s.e. RSwas between 0·80 ± 0·13 and 1·40 ± 0·16 at Dunwich, 1·30 ± 0·26 and 2·00 ± 0·33at Manly and 1·10 ± 0·10 and 2·20 ± 0·33 at Godwin Beach [Fig. 2(b)]. Mean ±s.e. H ′ values ranged from 0·00 ± 0·00 to 0·26 ± 0·11 at Dunwich, 0·15 ± 0·10 to0·59 ± 0·14 at Manly and 0·07 ± 0·07 to 0·59 ± 0·15 at Godwin Beach [Fig. 2(c)].



Table I. Numbers (n) and per cent contributions of tide-pool fishes caught from soft sedimenttide pools at Dunwich, Manly and Godwin Beach between January 2009 and December 2009

Dunwich Manly Godwin Beach

Species n % n % n %

GobiidaeFavonigobius exquisitus — — 164 36·77 198 45·41Favonigobius lentiginosus 429 88·80 — — 67 15·37Pseudogobius sp. — — 140 31·39 — —Acentrogobius caninus — — 18 4·04 11 2·52Arenigobius bifrenatus — — 15 3·36 43 9·86Arenigobius frenatus — — — — 1 0·23

SillaginidaeSillago spp.* 51 10·37 20 4·26 115 25·46

GerreidaeGerres subfasciatus 2 0·41 3 0·67 1 0·23

AtherinidaeAtherinomorus vaigiensis 1 0·21 — — 2 0·46

TetraodontidaeTetractenos hamiltoni 1 0·21 — — — —

BlenniidaeOmobranchus punctatus — — 84 18·84 — —Istiblennius edentulus — — 2 0·45 — —

SoleidaeSynaptura nigra — — 1 0·22 — —

SygnathidaeSyngnathoides biaculeatus — — — — 1 0·23

PlatycephalidaePlatycephalus fuscus — — — — 1 0·23

Total 482 446 436

*Species of juvenile Sillago cannot be readily differentiated <80 mm standard length (Weng, 1983).

The mean ± s.e. J ′ were between 0·00 ± 0·00 and 0·37 ± 0·15 at Dunwich, 0·15 ±0·10 and 0·66 ± 0·14 at Manly and 0·10 ± 0·10 and 0·65 ± 0·14 at Godwin Beach[Fig. 2(d)].

Table II. Summary of the results obtained in the repeated measures ANOVA of the temporal(month) and spatial (site) effects on volume of soft sediment tide pools at the three sites

Source of variation SS d.f. MS F P

Between subjectsSite 222·07 2 111·04 8·82 0·01Error 339·98 27 12·59Within subjectsMonth 323·81 6·54 49·54 2·90 >0·05Month × site 477·06 13·07 36·49 2·14 0·01Error (month) 3010·11 176·48 17·06



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Fig. 2. Mean ± s.e. monthly (a) abundance of fishes, (b) species richness (RS), (c) Shannon–Wiener’s diver-sity index (H ′) and (d) Pielou’s evenness index (J ′) ( , Dunwich; , Manly; , Godwin Beach; seeFig. 1).

Repeated measures ANOVA showed that the numbers of fish l−1 occupying softsediment pools were significantly different throughout the year and among the threesites. RS and H ′ were significantly different between sites, but not months. J ′ showeda significant difference between sites and months. RS, H ′ and J ′ showed no sig-nificant difference in the interaction between months and sites (Table III). Tests forseasonal differences of the number of fishes l−1 showed no significant differencebetween the three sites or within seasons at each site (Table IV).

PERMANOVA of the fishes l−1 showed a significant multivariate interactionbetween factors site and month (Table V), thereby indicating that fish assemblagesdiffered spatially and temporally. The MDS plot represents 360 points, 10 for eachmonth at each site. The plot showed no distinct groupings of pools among sites;however, the low stress level of 0·04 indicated a good ordination (Fig. 3).

The rs between volume and all the community variables showed a high degreeof concordance (Table VI). The J ′ at Manly were the only community variable notcorrelated with pool volume (P > 0·05).

Rarefaction curves of the three sites show that the number of expected speciesin Manly and Godwin Beach was greater than for Dunwich (Fig. 4). In addition,the s.d. of Dunwich did not overlap with Manly or Godwin Beach, indicating thatspecies diversity was poorer at this site.

The five most common species sampled were: F. lentiginosus, F. exquisitus,Pseudogobius sp., Sillago spp. and O. punctatus. ANOVA revealed that only



Table III. Summary of the results obtained from the repeated measures ANOVA of thetemporal (month) and spatial (site) effects on fishes l−1 (n), species richness (RS), diversity

(H ′) and evenness (J ′)

Assemblage variable Source of variation SS d.f. MS F P

n Between subjectsSite 41·32 2 20·66 6·38 0·05Error 87·45 27 3·24Within subjectsMonth 101·85 5·61 18·17 3·82 0·00Month × site 116·51 11·21 10·39 2·18 <0·05Error (month) 720·05 151·39 4·76

RS Between subjectsSite 26·45 2 13·23 9·62 0·01Error 37·11 27 1·37Within subjectsMonth 14·08 9·83 1·43 1·84 >0·05Month × site 21·15 19·66 0·62 0·80 >0·05Error (month) 206·19 265·35 0·78

H ′ Between subjectsSite 8·44 2 4·22 16·03 <0·01Error 7·11 27 0·26Within subjectsMonth 2·49 9·88 0·37 1·75 >0·05Month × site 2·89 19·76 0·15 1·02 >0·05Error (month) 38·41 266·81 0·14

J ′ Between subjectsSite 9·25 2 4·63 20·06 <0·01Error 6·23 27 0·23Within subjectsMonth 3·62 10·71 0·34 2·04 <0·05Month × site 3·35 21·42 0·16 0·94 >0·05Error (month) 48·02 289·11 0·17

F. lentiginosus (P < 0·001) and Sillago spp. (P < 0·001) abundances were sig-nificantly different among months (Fig. 5). Tukey’s post hoc tests showed thatF. lentiginosus abundances were significantly different between September and

Table IV. Summary of the results obtained from the repeated measures ANOVA of theseasonal effects on the number of fish l−1

Source of variation SS d.f. MS F P

Between subjectsSite 13·06 2 6·53 2·33 >0·05Error 159·86 57 2·81Within subjectsSeason 4·09 2·46 1·66 0·69 >0·05Season × site 22·31 4·92 4·53 1·89 >0·05Error (season) 337·23 140·26 2·40



Table V. PERMANOVA table of abundances of fish l−1

Source of variation d.f. SS Pseudo-F P (permutation)

Site 2 4·5256E5 116·83 <0·001Month 11 69 418 3·26 <0·001Site × month 22 75 657 1·78 <0·001Residual 324 6·2752E5

April (P < 0·05) and May (P < 0·05) and between October and April (P < 0·001)and May (P < 0·001). Tukey’s post hoc tests for Sillago spp. showed significantdifferences between March and May (P < 0·01), June (P < 0·05), July (P < 0·01)and August (P < 0·05), between October and April (P < 0·05), May (P < 0·01),June (P < 0·001), July (P < 0·001) and August (P < 0·01) and between Novemberand May (P < 0·05), June (P < 0·05), July (P < 0·01) and August (P < 0·05).

The LS frequency data from the more common fishes sampled throughout the yearshowed that most fishes were juveniles, yet some adult F. lentiginosus were found(Fig. 6). Although there was a lack of adult fishes using the tide pools, juveniles ofspecies of commercial importance, such as Sillago spp. (Fig. 7), were observed.

DISCUSSION

This study provides the first temporally extensive sampling of soft sediment tidepools in a subtropical environment. The only previous report on fishes occupyingsoft sediment tide pools in this region of Australia was that of Meager et al. (2005),

Fig. 3. Multidimensional scaling ordination plot of fish communities at Dunwich ( ), Manly ( ) and GodwinBeach ( ). Stress = 0·04.



Table VI. Correlations (Spearman rs) between mean abundance (n), species richness (RS),diversity (H ′) and evenness (J ′) with pool volume

n RS H ′ J ′

Site rs P -value rs P -value rs P -value rs P -value

Dunwich 0·313 *** 0·252 ** 0·280 ** 0·280 **Manly 0·244 ** 0·230 * 0·214 * 0·098 NSGodwin Beach 0·417 *** 0·280 ** 0·238 ** 0·182 *

*P < 0·05; **P < 0·01; ***P < 0·001; NS, not significant (P > 0·05).

who observed the Godwin Beach area for only 5 months and found 245 individualsfrom 12 species and five families. During the present study, 15 different speciesfrom nine families of fishes were found occupying tide pools during low tide. Dueto the ephemeral nature of soft sediment pools, different pools were sampled eachmonth, yet fishes were found in pools throughout the year. The most prevalent fishfamily observed was the Gobiidae, which dominated the pools at all three sites inthe bay. This result is consistent with rock pool studies where gobies also tendto dominate (Griffiths, 2003b; Castellanos-Galindo et al., 2005; Arakaki & Tokeshi,2006). Gobiidae are found in all biogeographic regions (Whitfield, 2005) and usuallyhave adaptations suited for intertidal life, including tolerances for high temperaturesand salinities (Fanta, 1997) and low dissolved oxygen (Martin, 1995).

15

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Fig. 4. Estimated mean ( ) ± s.d. ( ) species richness as a function of sample size of fish assemblages insoft sediment tide pools collected at Dunwich ( ), Manly ( ) and Godwin Beach ( ).



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Fig. 5. Mean ± s.e. number of individuals per pool of the dominant species (a) Favonigobius lentiginosus,(b) Favonigobius exquisitus, (c) Pseudogobius sp., (d) Sillago spp. and (e) Omobranchus punctatuscaught each month at Dunwich ( ), Manly ( ) and Godwin Beach ( ).

The overall abundance of fishes was significantly different among sites with Manlyhaving the highest abundance. Species richness, diversity and evenness indices wereall lowest at Dunwich, which was supported by the rarefaction estimates of speciesdiversity. This is an unusual result as the mean size of the pools at Godwin Beachwas significantly smaller than Dunwich, suggesting that fish occupation may be dueto some intrinsic factor such as the type of soft substratum (i.e. sand and mud) at eachsite. Soft substratum pools lack the structural complexity, such as shelter providedby cobble, crevices and algae, that is often related to increased species richness anddiversity in rock pools (Bennett & Griffiths, 1984; Griffiths et al., 2006), although



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Fig. 6. Standard length (LS) frequency of Favonigobius lentiginosus during Australian (a) summer (n = 137),(b) autumn (n = 181), (c) winter (n = 103) and (d) spring (n = 75).

they may contain detritus and sparse seagrass (pers. obs.). The lack of complexityin soft substrata pools makes these fishes potentially more prone to predation bybirds, but there may be some trade-off that makes the persistent occupation of theseephemeral pools, at least by some life-history stages, advantageous. Alternatively,



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Fig. 7. Standard length (LS) frequency of Sillago spp. during Australian (a) summer (n = 59), (b) autumn(n = 41), (c) winter (n = 5) and (d) spring (n = 81).

gobiids may have developed specialized adaptations for coping with isolation in tidepools when the tide recedes. Kruck et al. (2009) suggested that Sillago spp. benefitfrom the use of soft sediment pools for prolonged access to intertidal meiofaunaand temperature-induced increases in growth. Nonetheless, the persistent occupationof pools by fishes suggests that tide-pool use by the species sampled is probably



beneficial, but it may also be a result of fishes getting trapped as the tide recedesand before they can reach the sub-tidal zone.

Abundance was also significantly different between months, but no particularpattern was observed. Repeated measures ANOVA also showed that there was nosignificant difference in number of fishes l−1 between seasons, which supports thehypothesis that the soft sediment tide pools in this study reflect patterns of a tropicalsystem. Studies of temperate rock pools have shown that peaks of abundance correlatewith recruitment of particular species (Willis & Roberts, 1996; Griffiths, 2003b).When looking at individual species, F. lentiginosus and Sillago spp. showed peaksof abundance that could be attributed to recruitment. Sillago spp. had two peaks ofabundance that could be due to recruitment of the three species that occur withinMoreton Bay at different times, but identification to species level would requiregenetic analysis as they are not visually identifiable (Kruck et al., 2009). Nonetheless,the individual peak occupations did not correlate with any overarching trend ofseasonality.

The positive Spearman correlation between pool volume and abundance was sim-ilar to that found by Meager et al. (2005) as well as in studies on rock pools(Prochazka & Griffiths, 1992; Mahon & Mahon, 1994). This positive correlationwas to be expected, as there is more space available and presumably more resourcesfor the fishes to utilize at low tide and the likelihood of finding a large pool is greaterthan a small pool. Although a study of rock pools found that food resources werenot a limiting factor for fish densities (Silberschneider & Booth, 2001), this has notbeen tested in soft sediment pools. In rock pools, greater pool volume correlates withincreased colonization rates (Pfister, 1998), however, with the high turnover of softsediment pools fish occupation probably occurs as a function of need, preference orboth. Unfortunately, information about the behaviour of these species on the ebbingtide, particularly how they discriminate between areas that will become pools whenthe tide ebbs and avoid those that become bare sand, is lacking but of considerableinterest.

The role of tide pools acting as nurseries for juvenile fishes is well documented inthe literature for rock pool habitats (Bennett, 1987; Mahon & Mahon, 1994; Gibson& Yoshiyama, 1999) and to a lesser extent in soft sediment pools (Kruck et al., 2009).The results of the present study help establish the role of intertidal habitats, partic-ularly soft sediment tide pools, as nurseries for a few of the fish species selected,predominantly Sillago spp., O. punctatus and Favonigobius spp. The majority offishes sampled were juveniles with the only adults belonging to the Gobiidae andBlenniidae. This is not surprising as some members of these two families are usu-ally considered permanent residents of tide pools (Castellanos-Galindo et al., 2005).Nonetheless, the juveniles were either taking refuge from sub-tidal fish predators orusing the pools for some other benefits to being isolated at low tide.

The results of this study demonstrate the frequent use by fishes in soft sediment tidepools throughout the year. These relatively homogeneous sand- and mud-flat poolsare important habitats for the fishes that occupy them; the assemblages are recurrentand differ little in structure throughout the year, which is the pattern of occupancyobserved in tropical rock pools (Castellanos-Galindo et al., 2005). Whether it is ona permanent basis (i.e. Gobiidae) or temporary (i.e. Sillaginidae), these ephemeralmicrocosms play a role in the life cycles of some coastal fishes. Soft sediment tidepools are also likely to be important for birds and fishes that rely on these small fishes



as prey such as the flathead Platycephalus speculator Klunzinger and the cormorantPhalacrocorax melanoleucos (Humphries et al., 1992). Soft sediment tidal flats areoften overlooked in environmental management plans and should be considered inthe future as essential habitats for small fishes that either live in them or use themtemporarily. Some possible management strategies could include creating pools atsoft sediment shore sites to ensure there are viable habitat refuges, or decreasinghuman traffic. Dunwich, the site with the least diverse and abundant fish assemblages,is subjected to high amounts of foot traffic by student groups, which could explainthe results of this study. Soft sediment tide pools need to be protected, especiallywith respect to the shores of Moreton Bay tide pools that are unique and diverse.

We would like to thank A. Chelsky, B. Gilby and J. Large for assistance in the field. Wewould also like to thank two anonymous reviewers for their suggestions and input.

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Community structure of soft sediment pool fishes in Moreton Bay, Australia

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