Journal of Experimental Marine Biology and Ecology 366 (2008) 151–159

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Journal of Experimental Marine Biology and Ecology

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Interpreting molluscan death assemblages on rocky shores: Are they representativeof the regional fauna?

Stephen D.A. Smith ⁎School of Environmental and Rural Science, University of New England, National Marine Science Centre, PO Box J321, Coffs Harbour NSW 2450 Australia

⁎ Tel.: +61 2 66483908; fax: +61 2 66516580.E-mail address: ssmith@nmsc.edu.au.

0022-0981/$ – see front matter © 2008 Elsevier B.V. Aldoi:10.1016/j.jembe.2008.07.019

a b s t r a c t

a r t i c l e i n f o

Keywords:

BivalvesCollectingGastropodsRegionalNearshoreSurrogatesTaxonomic distinctness

Recent work has suggested that molluscan death assemblages in marine intertidal habitats are sufficientlyrepresentative of regional biodiversity to be used in rapid, comparative biodiversity assessments. If this canbe shown to be a general property of death assemblages, they may be a valuable surrogacy tool, especially incountries such as Australia where comprehensive species lists are unavailable for many regions. To test this, Iconducted surveys of death assemblages associated with 10 headlands within the Solitary Islands MarinePark, northern NSW, Australia. Species lists for each site were analysed to determine: i) average taxonomicdistinctness (Δ+) - the degree to which species within a sample are related to each other; and ii) variation intaxonomic distinctness (Λ+) - the evenness of distribution of species across higher taxonomic levels. Thevalues of these biodiversity indices were then compared to equivalent measures determined from lists ofnearshore taxa and of taxa occurring more widely in the region. Species richness in death assemblagesranged from 99-161 species across the 10 sites. Analyses of representativeness indicated that species recordsfrom a single site were unlikely to adequately represent regional diversity but that a random combination ofdata from 2 or more sites was fully representative of nearshore diversity and of regional diversity of bivalves.Regional diversity of gastropods was poorly represented in these nearshore death assemblages; this wasprimarily due to under-representation of a number of dominant families. These patterns are most likely dueto a combination of factors including recruitment processes and availability of suitable habitats, both ofwhich differ over the cross-shelf gradient, and the influence of targeted removal of “collectable” species.Despite the disjunct geographical settings of this study and previous work (Isles of Scilly, UK), the proportionof the species pool contained in death assemblages was remarkably similar; further study from a range oflocations, will help to determine the generality of such patterns.

© 2008 Elsevier B.V. All rights reserved.

1. Introduction

The documentation of biodiversity across a range of habitats isa continuing priority for scientists and managers alike. While com-prehensive lists of species and their relative abundances provide theoptimum data for long-term assessment, planning andmanagement,the impracticality of achieving such a goal in marine systems inmanygeographic regions is becoming increasingly evident given the vastareas to be covered, the relative inaccessibility of most habitats, andthe massive diversity revealed by detailed observations (e.g. Bouchetet al., 2002). For this reason, the use of surrogates has attractedconsiderable research effort and a number of authors have advocatedthe use of different taxa in different habitat types (Ward et al., 1999;Olsgard and Somerfield, 2000; Olsgard et al., 2003; Magierowski andJohnson, 2006; Gladstone, 2007). One taxon that has shown

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particular promise for intertidal rocky shores is the molluscs whichoften dominate both species richness and abundance. Molluscs havebeen shown to be the most suitable surrogate for broader biodi-versity in terms of their ability to: reflect broad-scale patterns ofcommunity structure (Smith, 2005); predict species richness atmedium spatial scales (Smith, 2005); and for conservation planning(Gladstone, 2002; Gladstone and Alexander, 2005). While focusingsolely on molluscs reduces the requirement for taxonomic expertiseacross a range of taxa, and may reduce survey time appreciably, thespatial scope of surveys may still prove costly in terms of field time(Smith, 2005).

During investigations of molluscs on rocky shores in sub-tropicaleastern Australia, it became apparent that most species living on rockyshores can be found in local death assemblages, which are oftenextensive, particularly on leeward shores with well developed plat-forms and complex topography. These observations, reinforced byrecent studies evaluating beach-washed death assemblages in the UK(Warwick and Light, 2002; Warwick and Turk, 2002), suggested thataggregations of dead shells may be useful indicators of biodiversityover regional scales.

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The use of death assemblages to reconstruct putative living as-semblages is not new and is a key tool in palaeoecological investiga-tions of community structure, especially in soft sediment habitats(Kidwell and Bosence,1991; Kidwell, 2002). Most of these studies havefound that death assemblages strongly represent the species richnessof living faunawith from 60-100% of species found alive also occurringas dead shells (Kidwell and Bosence, 1991; Kidwell, 2001). In mostcases, death assemblages contained substantially (2-3 times) morespecies than living assemblages, primarily as a result of time-averaging(i.e. passive sampling over sometimes extensive periods of time)(Kidwell, 2001). For this reason, and providing that accumulation hasnot occurred over very extensive time periods (i.e. so that some speciesno longer occur in the region), death assemblages are potentiallymore useful targets for rapid assessments of regional diversity thanone-off surveys of living fauna (Warwick and Light, 2002). However, inorder for this to be the case, living and dead assemblages on rockyshores need to show similar, high levels of fidelity to those from softsediments. The relatively harsh and dynamic nature of intertidal rockyshores (i.e. semi-diurnal disturbance due to tidal action, periodic stormactivity, strong forces promoting shell fragmentation) generates theexpectation that this may not be the case. However, Rose and Smith

Fig. 1. The Solitary Islands Marine Park showing the 10 rocky shores at w

(unpublished data) showed that 87% of species found alive on rockyshores in the NSW north coast region also occurred in adjacent deathassemblages which were also, on average,1.53 times richer than livingassemblages. Thus, these encouraging, initial results suggest that deathassemblages may be useful for gaining insight into regional biodiver-sity. This paper tests this prediction using data from 10 headlandssampled over a 6-week period in 2004.

2. Methods

2.1. Site description

The Solitary Islands Marine Park extends for approximately 70 kmalong Australia's eastern, subtropical coastline (Fig. 1) and supportsdiverse marine communities comprising species with temperateaffinities, tropical affinities and regional endemics (Harriott et al.,1994; Smith, 2000). The coastal section of the park includes a numberof well-developed, mostly headland-associated, rock platforms uponwhich habitat diversity is high, as is biodiversity (Smith, 2005). Agroup of small rocky islands (the Solitary Islands), with associatedfringing, rocky reefs, are scattered across the shelf, with distances

hich molluscan death assemblages were surveyed during this study.

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from shore ranging from approximately 2 to 11 km (Fig. 1). Patch reefsare common throughout the marine park with current estimatesindicating that they account for approximately 25% of benthicsubstrata (but note that bottom-typing is incomplete for the region).

The predominant swell direction is from the south-east givingrise to strong exposure gradients; northward-facing shores aregenerally sheltered and characteristically act as depositionalareas for a range of flotsam and jetsam. It is on these northernshores that well-developed molluscan death assemblages arecommonly found, often forming concentrated and relatively-spatially-stable (i.e. located in the same part of the shore over

Fig. 2. Confidence funnels (mean and 95% probability intervals) of average taxonomic distinmaster list showing the range of values displayed by samples from 10 headlands (abbreviatiowell as individually for each class. The number of species is shown on the x-axis.

time) shell banks (Smith and Rose, pers. obs.). These shell bankswere targeted in this study.

2.2. Field methods

Pilot studies, during which cumulative species richness was deter-mined over 10-min intervals for a maximum survey period of 3 hr,were conducted in order to optimize the sampling methodology.Surveys were conducted at least twice at each of a number of differentlocations and the results were used to construct species accumulationcurves (Ugland et al., 2003). From these curves, it was apparent that a

ctness (Δ+) and variation in taxonomic distinctness (Λ+) generated from the nearshorens as in Fig. 1). Plots are presented for all gastropod and bivalve species (total species) as

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2-hr survey periodwas optimal (i.e. the curve became asymptotic) andwas therefore adopted as the standardised sampling unit.

The abundance of species in death assemblages can be very highindeed. As such, itwas not practicable, nor desirable given the objectivesof the study, to determine total abundance of each species. In addition,vagaries of currents, the history of wave activity and other local factorscan strongly affect abundance values which can consequently bedifficult to interpret. However, it became apparent during the pilotstudies that there were often obvious differences in the relativeabundance of some taxa between some sites and so a semi-quantitativescoring system was used to summarise this. The scoring system wasbased on a log3 scale: score 1=1-3 individuals; 2=4-10; 3=11-30; 4=31-

Fig. 3. Confidence funnels (mean and 95% probability intervals) of average taxonomic distimaster list showing the range of values displayed by samples from 10 headlands (abbreviatiowell as individually for each class. The number of species is shown on the x-axis.

100; 5=101-300; 6N300 (Smith et al., 2008). Although the subsequentanalyses only took presence-absence data into consideration, thisinformation is included here to provide a complete account of thesampling method. A total of 10 sites, each of which supported well-developed shell banks, was evaluated for the study (Fig. 1) which tookplace over a 6-week period in March-May 2004.

At each site, surface searches (to a depth of approximately 150mm)were conducted across the spatial extent of the primary shell bank andall species of gastropod and bivalve ≥5 mm were documented andgiven an abundance score. As shells in death assemblages are oftenworn and/or fragmented, identification was sometimes difficult andspecies were only included if fragments could be unambiguously

nctness (Δ+) and variation in taxonomic distinctness (Λ+) generated from the regionalns as in Fig. 1). Plots are presented for all gastropod and bivalve species (total species) as

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identified to species.While this approachwill almost certainly result inthe under-estimation of species richnesswithin a shell bank, it allowedfor standardisation across the study.

Representative specimens of all species were retained in areference collection and were initially identified using publishedresources (primarily Lamprell and Whitehead, 1993; Wilson, 1993,1994; Lamprell and Healy, 1998; Beechey, 2007). Identifications werelater confirmed using the collections of the Australian Museum.

2.3. Data processing and analysis

The primary objective of this study was to determine if thecollection of shells found in death assemblages was representative

Fig. 4. Confidence funnels (mean and 95% probability intervals) of average taxonomic distinmaster list showing the range of values displayed by randomized aggregations of from 2-5 hefor each point. The number of species is shown on the x-axis.

of regional mollusc diversity. In order to address this question, theTAXDTEST procedure in the PRIMER package (Clarke and Gorley,2006) was used. This procedure calculates the average taxonomicrelatedness for each sample (how far apart, in a taxonomic sense,are any two species chosen at random from the sample) andcompares this to the range of values calculated by repeatedly takingrandom samples of the same size (i.e. number of species), from amaster list of appropriate species (Clarke and Warwick, 2001;Warwick and Clarke, 2001; Smith and Rule, 2002; Warwick andLight, 2002; Warwick and Turk, 2002; Leonard et al., 2006). Theoutputs of the analysis include statistics which summarise theaverage taxonomic distinctness (AvTD, Δ+) and the variation intaxonomic distinctness (VarTD, Λ+). Each statistic can be compared

ctness (Δ+) and variation in taxonomic distinctness (Λ+) generated from the nearshoreadland samples. Numerals represent the number of samples pooled to generate the data

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against the expected distribution derived from a master list pro-viding a test of representativeness.

In regions, or for taxa, whose biota are well known, master listsare readily compiled from published records and/or appropriatedatabases. However, in regions where such information is relativelypoor, generation of a master list can be a difficult and drawn-out process. In the present case, the regional master list was ini-tially compiled from records held by the Australian (Sydney) andQueensland (Brisbane) museums for species occurring down to40 m depth (i.e. shallow-water taxa); this was supplemented withdata derived from collections held by local enthusiasts and fromextensive personal observations. Species were allocated into higher

Fig. 5. Confidence funnels (mean and 95% probability intervals) of average taxonomic distimaster list showing the range of values displayed by randomized aggregations of from 2-5 hefor each point. The number of species is shown on the x-axis.

taxonomic classifications using the scheme outlined in Beesley et al.(1998).

The compilation of usable list took in excess of 3 yr. However, alimitation with any species list derived for this region is that it will beout-of-date relatively rapidly given the highly dynamic nature of thespecies pool, putatively,mainly due to sporadic recruitment of larvae oftropical taxa from the East Australian Current (e.g. Harriott et al.,1994).Thus, repeated observations at a range of key sites inevitably leads toadditions to the regional species list. However, many of these speciesoccur in very low abundance, often as single specimens (Smith, 2001,2003) and their omission from the master list is highly unlikely toaffect the conclusions of this study.

nctness (Δ+) and variation in taxonomic distinctness (Λ+) generated from the regionaladland samples. Numerals represent the number of samples pooled to generate the data

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Much of the research effort leading to the compilation of specieslists for the marine park has focused on subtidal reefs fringing theoffshore islands, all of which lie at least 2 km from shore. Giventhat many of the tropically-affiliated species have only been recordedfrom island sites, it was considered highly improbable that deathassemblages from coastal rock platformswould be fully representativeof regional diversity. Tests were nevertheless run comparing samplesto the full regional master list; however, a reduced list of speciesrecorded from nearshore sites (defined as b2 km from shore andincluding headlands, headland-associated reefs, nearshore patch-reefs and nearshore soft-sediment habitats) was also compiled foradditional comparisons (nearshore master list).

3. Results

Species richness across the 10 headlands ranged from 99-161taxa. Species lists from each of the sites were compared against thenearshore master list of 433 species (99 bivalves and 334 gastropods)and the regional master list of 628 species (150 bivalves and 478gastropods). Comparisons of the nearshore with the regional masterlist indicated that average taxonomic distinctness was similar(P=0.446) but that variation in taxonomic distinctness (Λ+) valueswere on the lower boundary of the 95% confidence intervals (P=0.050). This indicates that the nearshore list is not simply a randomsubset of the regional list; the differences reflect processes occurringalong the nearshore-offshore gradient (see later).

3.1. Comparisons against the nearshore master list

Analyses of the representativeness of samples from each headland(Fig. 2 - top) clearly demonstrate that 5 of the 10 have average tax-onomic distinctness (Δ+) values that fall outside the 95% probabilityfunnel and are thus unrepresentative of the nearshore species pool.There was no evidence of systematic bias related to differences inspecies richness between samples as those thatwere unrepresentativespanned the full range of species richness encountered across sites(Fig. 2). Samples from the other 5 sites were all strongly representativeof the nearshore fauna, not only falling within the 95% probabilityfunnel but also lying close to the mean value (Fig. 2). The results forvariation in taxonomic distinctness (Λ+) similarly showed that samplesfrom 5 headlands lay outside the 95% probability intervals, indicatinglower than expected values.

A similar study (Warwick and Light, 2002) conducted in the Isles ofScilly suggested that lack of representativeness of the total mollusccollection resulted primarily from under-representation of bivalves inassemblages. In order to determine if this was also the reason fordeviation from expected values in this study, additional analyses wereconducted for gastropods and bivalves separately (Fig. 2 – middle andbottom). The results indicate that a single sample is likely to berepresentative for bivalves and, with the exception of one sample (Δ+

for gastropods from Diggers Camp – P=0.038), data points forgastropods also fall within the 95% probability intervals for bothstatistics. The combination of both classes into one data set clearly anddramatically amplifies departures from expected values.

3.2. Comparisons against the regional master list

Comparisons against the regional master list for the total speciescomplement provided patterns for Δ+ that were almost identical tothose returned by the comparisons to the nearshoremaster list (Fig. 3).That is, 5 samples showed values that were significantly lower thanexpected while the other 5 were close to the mean of expected values(Fig. 3 – top). While the patterns for Λ+ were also similar, there was ageneral decrease in value relative to comparisons with the nearshoremaster list, resulting in 8 of the 10 samples falling significantly belowthe expected range. Comparisons were once again performed sep-

arately for the 2 classes. In this case,while all samples showed values ofboth Δ+ and Λ+ that were within the 95% probability intervals forbivalves, 7 out of the 10 gastropod sampleswere significantly above theexpected range for Δ+ and one was significantly above the range for Λ+

(Fig. 3).

3.3. Aggregation of data

From the results presented above, it is clear that while a singledeath assemblage may be representative of nearshore and regionalbivalves, it can not be guaranteed to provide a reliable indication ofgastropod, or total, diversity. Questions following on from this are:i) does the pooling of data from a number of sites lead to improvedrepresentativeness?; and ii) if so, howmany sites need to be evaluatedto ensure representativeness? To address this, random pooling ofdata from sites was conducted, generating samples representing 2-5headlands (10 pairs,10 triplets, 5 quads and 5 quins). These aggregatedspecies lists were then compared to both the nearshore and regionalmaster lists for total species, and also, separately for gastropods andbivalves.

The results for nearshore comparisons (Fig. 4) indicated that, forΔ+, at least 1 sample, for each set of aggregations of between 2-5headlands, continued to show significant differences from expectedvalues for total species richness. At least 2 samples from each ag-gregated set were also significantly different to the expected values forΛ+ (Fig. 4 - top).

When the data were subdivided into the two classes, any combina-tion of 2 or more headlands was found to be fully representative ofnearshore gastropods for bothΔ+ andΛ+ (Fig. 4–middle).While thiswasalso the case for average taxonomic distinctness of bivalves (Fig. 4 –

bottom), one pair and 2 triplets returned Λ+ values that were sig-nificantly below the expected range.

Surprisingly, at least for Δ+, the data set for total species performedbetter against the regional list (Fig. 5 - top), indicating that any com-bination of 3 or more headlands would provide representative data.However, this was not the case for Λ+ which, compared to the resultsfor nearshore comparisons, showed a substantial shift downwardswith themajority of samples falling outside the 95% probability funnel.The comparisons by class indicated that, for bivalves, any combinationof samples was fully representative of the regional fauna (Fig. 5 –

bottom). However, for gastropods, while the majority of sample com-binations were within expected values for Λ+, only one was within theexpected range for Δ+ (Fig. 5 – middle).

4. Discussion

It is clear from the results of this study that evaluation of deathassemblages at a single site can provide a representative sample ofboth nearshore and regional bivalves. Pooling of data from 2 or moresites will provide a fully representative sample of nearshore gastro-pods and also of regional bivalves, but not of regional gastropods andnearshore bivalves. In contrast, assessments of gastropods are likely tobe highly unrepresentative of regional diversity regardless of howmany headland sites are evaluated (within the range of this in-vestigation at least). The fact that any single site was fully representa-tive of regional bivalve diversity, but some pairs of sites were not,clearly requires further explanation. While this initially appears to becounter-intuitive (i.e. the addition of more sites should improverepresentativeness), the reason for this appears to be that most of thespecies thatwere added in progressive poolingwere from families thatwere already represented. Thus, while the pool of species wasincreased, the spread across higher taxa was not, leading to reducedvalues ofΛ+ (Clarke andWarwick, 2001). This raises an important pointfor the wider application of these methods – progressive sampling ofvery similar habitatsmayactually lead to less representative samples ifhigher taxa are highly habitat specific. For future studies, therefore, if

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the objective is to collect samples which are representative ofbiodiversity at a broad scale, it would be prudent to target a suite ofsites that, together, might be expected to accumulate shells from awide range of habitats.

With respect to the relative representativeness of the 2 dif-ferent classes, the patterns in this study contrast with those found byWarwick and Light (2002) who identified the paucity of bivalves, andtheir skewed representation to soft-sediment-associated taxa, asthe primary reason why beach collections were unrepresentative ofregional lists. There are a number of possible reasons for thesecontrasting results. Firstly,while the death assemblages sampled in thepresent study were all on rocky shores, each site was flanked byextensive sandy beaches and much of the immediate offshore habitatcomprises soft sediments. Rocky-shore-associated bivalves were wellrepresented in collections and, while soft-sediment taxa always hadlow abundance at most sites, they were consistently present. Thediversity of these taxa was not particularly high, but clearly theyspanned the taxonomic tree sufficiently to provide a representativesample.

It was the gastropods that showed the greatest departure fromexpected values at the regional level. The primary reason for this lack ofrepresentation, as suggested by the average taxonomic distinctnessvalues that are significantly higher than expected, appears to be theunder-sampling of taxa from the most speciose families; such ascenario would lead to higher average path-lengths. Table 1 shows thespecies richness of dominant families for both the regional andnearshoremaster lists and for the data from the 10 headlands (pooled).On average, samples contained 42% of the regional species pool byfamily; however, some families were clearly strongly under-repre-sented. The most obvious of these were: the Ovulidae, specimensof which were absent from all sites; the Costellariidae which wasrepresented by a single species (11% of the regional richness); theMitridae (17% of regional richness); the Conidae and Columbellidae(31% of regional species for both); the Cerithiidae (36% of regionalrichness); and the Terebridae (40% of regional species), which fell justbelow the average. If representation of the nearshoremaster list is alsoconsidered, the Cypraeidae can also be considered to be one of thefamilies that are under-represented in collections (Table 1).

Many of the regional species in these under-represented familieshave strong tropical affinity. Given the obvious and well documentedtendency for benthic communities to have increasing tropical in-fluence with distance from shore (related to frequency of exposure totropical waters entrained by the East Australian Current) (e.g. Harriottet al., 1994) it is perhaps unsurprising that they do not appear in shellbanks on headlands. This tendency is reflected not only in the analyses

Table 1Species richness of gastropod families showing the total number of species in theregional and nearshore master lists and in collections from 10 death assemblages(pooled)

Family Regional Nearshore Total found

Muricidae 50 37 (74) 25 (50, 68)Cypraeidae 45 37 (82) 22 (49, 59)Conidae 32 20 (63) 10 (31, 50)Turridae 25 16 (64) 12 (48, 75)Mitridae 23 9 (34) 4 (17, 44)Trochidae 19 16 (84) 14 (74, 88)Buccinidae 17 14 (82) 10 (59, 71)Columbellidae 16 11 (69) 5 (31, 45)Ranellidae 16 12 (75) 10 (63, 83)Cerithiidae 14 7 (50) 5 (36, 71)Fissurellidae 13 11 (85) 7 (54, 64)Ovulidae 10 3 (30) 0 (0, 0)Terebridae 10 5 (50) 4 (40, 80)Costellariidae 9 5 (56) 1 (11, 20)Naticidae 9 8 (89) 6 (67, 75)

Numbers in brackets in the nearshore column represent the percentage of the regionaltotal and, in the last column, percentage of the regional and nearshore totals, respectively.

for specific headland sites, but also in the finding that variation intaxonomic distinctness in the nearshore master list was lower thanexpected in comparisons with the regional master list. It is likely thattropically-affiliated species will seldom be transported to nearshorehabitats (as larvae). Further, those that do settle may not survive asrequisite habitats and food sources may not be present. For example,the relative lack of suitable octocorals in nearshore habitats (Smith andSimpson, 1991; Harriott et al., 1994) may be the primary reason whyovulids were not found in headland death assemblages.

Another issue to consider is that at least some of the under-represented families are highly prized by collectors and selective col-lecting could readily contribute to the observed results. The fact thatrarer species are more eagerly sought potentially compounds thepotential bias imposed by collecting. Over the course of my investiga-tions of death assemblages, collectors havebeen consistently observed,in some cases, with considerable effort invested in these activities (e.g.daily raking of shell banks atWoolgoolga Headland). Although some ofthe sites are putatively protected from collecting by the marine parkzoning plan, enforcement is discontinuous and compliance is conse-quently less than 100%.

A further source of bias in death assemblages is that delicate orfragile species are unlikely to be present, especially in high energysettings (e.g. Kidwell and Bosence,1991). If delicate forms predominatewithin a family, this could readily lead to under-representation indeath assemblages. However, in this case, most of the species infamilies that were under-represented are quite robust (even theOvulidae which are often found intact in death assemblages at theouter Solitary Islands – pers. obs.). For this reason, this potential sourceof bias is unlikely to be an important contributor to the patternsobserved in this study.

Despite the fact that the mollusc communities evaluated duringthis study were approximately 2-3 times (nearshore), and 3-4 times(regional), more diverse than those sampled by Warwick and Light(2002), and that the study was conducted on subtropical rocky shoresin eastern Australia, rather than a temperate beach in the UK, there aresome strong and encouraging similarities between the 2 studies. Thefirst, and most obvious, is that assessments of death assemblages canprovide adequate representation as long as sufficient samples aretaken and that the spatial scale embodied in the master list is realistic.The second relates to the proportion of master-list-species that wererepresented in death assemblages. In this study, individual sitessupported from 16-26% of regional species (average=22.6%) and from23-37% of nearshore species (average=32.8%). Similar surface searches(by RMW) conducted in the Isles of Scilly recorded 32% of the taxa fromthe region (Warwick and Light, 2002). This remarkable similarity to thenearshore figures in this study (bearing in mind that samples wereonly found to be fully representative of the nearshore list), if found tobe a more general property of death assemblages sampled in this way,may be particularly useful given the circumstances in which assess-ments of death assemblages have most potential. Arguably, one of theprimary applications of these methods is the assessment of biodiver-sity in regions where such data are lacking. However, this raises somemajor difficulties, the most important of which is that there is no waythat the representativeness of samples can be assessed as master listswill be unavailable. To a certain extent, this problem can be obviated ifdeath assemblages contain a consistent proportion of the species pool.Clearly, given the range of circumstances under which death as-semblages form, meaningful predictions from only 2 sets of datashould be viewed with extreme caution. I have commenced furthertesting, at a range of different geographical locations, to determine ifthis is a more general property of intertidal death assemblages.

In conclusion, the emerging pattern is that death assemblages canbe used to provide a representative indication of diversity, as long assome of the specific constraints of the local and regional environmentare considered. In the present context, sampling of a single site (asdone by Warwick and Light, 2002) is clearly inadequate to provide

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reliable representation of total species in nearshore habitats, whichcould only be guaranteed by visiting 2 or more sites. One of the waysin which representation can be maximized is by targeting sites inslightly different ecological settings in order to ensure that thedifferent death assemblages passively sample across the main habitattypes present. Thus, in more recent work (unpublished data) I havesampled 3 intertidal sites at each major location but, whereverpossible, have chosen sites with different exposure levels (i.e. theorientation of the deposition site to the prevailing swell and currentpatterns) and with different combinations of surrounding habitats.While this appears to be the best approach for one-off studies inremote regions, if sites are accessible over longer periods of time,temporal replication may also be a useful approach. For example,Warwick and Turk (2002) found that a species list of dead shellscompiled from records of numerous collectors over time, at a singlebeach site, was fully representative of regional diversity. Thisobservation is currently being evaluated for the rocky-shore deathassemblages in subtropical eastern Australia.

Acknowledgements

The work presented here was inspired by discussions with RichardWarwickduring a period of study leave at PlymouthMarine Laboratoryin 2001. Harry Rose helped in the early stages of developing themethods and compiling the regional species lists. Ian Loch, DesBeechey (AustralianMuseum, Sydney) and ThoraWhitehead (Queens-land Museum, Brisbane) generously assisted with the identification ofmany of the species in the collections. Sampling was conducted underpermits from the NSW Marine Parks Authority and NSW Fisheries.Kathryn James produced Fig. 1. [SS]

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