*Corresponding author. E-mail: pbouchet@cimrs1.mnhn.fr

Biological Journal of the Linnean Society, 2002, 75, 421–436. With 7 figures

INTRODUCTION

The number of currently described marine species hasrecently been estimated to be 274,000, a mere 14.7%of the total 1.868 million species described (Reaka-Kudla, 1997). However, extrapolating from resultsobtained from box cores in the deep North Atlantic,Grassle & Maciolek (1992) speculated that the realnumber of deep-sea small macrofaunal invertebratescould be in the order of 10 million species and Lambshead (1993) even suggested that the oceanscould possibly teem with up to 100 million nematodespecies. The debate on described vs. actual numbers ofmarine species parallels that on described vs. actualnumbers of insects. Starting with the seminal work by Erwin (1982) on beetle species living in the canopyof a neotropical tree, speculations on the number of

insect species have proposed numbers ranging from 5 to 90 million species (Stork, 1988; Gaston, 1994; Ødegaard, 2000). Historically, the biologically lessdiverse (Rex et al., 1993; Crame, 2000) middle andhigh latitudes have received more attention frommarine biologists, and current inventories of the biotaof the seas of Europe, northern North America, NewZealand, or southern Africa, although incomplete tovarying degrees, are probably a fair reflection ofreality. Conversely, the tropics have received lessattention, and it has been estimated that the 93000currently described coral reef species might representonly 1–15% of the real number of species present(Reaka-Kudla, 1997). Molluscs have the largest diver-sity of any phylum in the marine environment, andmollusc diversity is exceedingly high in the tropicalwaters of the Indo-Pacific, particularly in coral reefenvironments. Gosliner et al. (1996) estimated thatapproximately 60% of all marine invertebrate speciesin this extensive region are molluscs.

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Assessing the magnitude of species richness in tropicalmarine environments: exceptionally high numbers ofmolluscs at a New Caledonia site

PHILIPPE BOUCHET1,2*, PIERRE LOZOUET1, PHILIPPE MAESTRATI1 and VIRGINIEHEROS1

1Muséum National d’Histoire Naturelle, 55 rue Buffon, 75005 Paris, France2Institut de Recherche pour le Développement, B.P. A5, Nouméa, New Caledonia

Earlier studies in the tropical Indo-Pacific have grossly underestimated the richness of macrofauna species at spatialscales relevant to conservation and management as a result of insufficient collecting and sorting effort. A massivecollecting effort involving 400 day-persons at 42 discrete stations on a 295-km2 site on the west coast of New Caledonia, south-west Pacific, revealed 2738 species of marine molluscs. This is several times the number of speciesrecorded from any area of comparable extension anywhere in the world. Spatial and habitat heterogeneity is highwith 32% of the species collected at a single station. With 20% of the species represented by single specimens (0.4%of all catches), rare species make up a considerable proportion of the fauna. This justifies the parallel drawn betweencoral reefs and rain forests in terms of species diversity. The real richness of many soft-bodied marine taxa is prob-ably underestimated, as evidenced by the fact that 28.5% of the mollusc species present at the study site are rep-resented in the samples only by empty shells. © 2002 The Linnean Society of London, Biological Journal of theLinnean Society, 2002, 75, 421–436.

ADDITIONAL KEYWORDS: coral reefs – diversity – inventory – post mortem remains – rarity – spatial heterogeneity.

Traditionally, biologists have used two approachesto describe levels of biological diversity in marine envi-ronments. One approach is that of quantitative ecolo-gists, who sample small surfaces (typically 0.1m2) onsoft bottoms, and use various indices to compare diver-sity in different ecological and biogeographical envi-ronments (e.g. Schlacher et al., 1998). Anotherapproach is that of biogeographers, who pool all dataon species recorded from a vast area (typically 100s or1000skm of coastline or 106 km2 of sea bottom or seasurface), and compare levels of species richness in dif-ferent parts of the world ocean (e.g. Veron, 1995). Bothapproaches are useful in their own right, but given the different scales of habitat heterogeneity, noneaddresses the issue of species richness at the spatialscale that is relevant to conservation and management(a bay, a stretch of coral reef, an island). Gosliner &Draheim (1996) pointed to the lack of baseline dataeven from localities believed to be well known: no esti-mates of the total number of species in any Indo-WestPacific coral reef system are available (Wells, 1998).

Molluscs are one of few phyla that are routinelytaken into consideration in marine biodiversitysurveys and are even considered to be an ‘appropriateindicator group’ for the rapid assessment of diversityof organisms inhabiting coral reefs (Wells, 1998).Because of the long interest of numerous professionalmalacologists and amateur shell collectors, the qualityof the information on patterns of marine molluscanspecies richness is surpassed probably only by that onfishes. However, much of the literature focuses on macromolluscs (‘seashells’) that can be collected by picking in the field, and tends to ignore or grossly underestimate the smaller species. This isprobably because micromolluscs require specific collecting/sorting attention and have a reputation topresent formidable taxonomic difficulties. Because ourtaxonomist perception of actual mollusc richness didnot seem to be adequately reflected in the publishedliterature, fieldwork was conducted specifically to document molluscan richness for all size classes in a complex tropical coastal environment. The presentpaper reports on such patterns of marine molluscanspecies richness at a New Caledonia site.

MATERIAL AND METHODS

GEOGRAPHICAL SETTING

The study site is the coral reef lagoon of Koumacbetween 20°30¢ and 20°45¢ S, on the north-west coastof New Caledonia, south-west Pacific (Fig. 1). It wasselected because the mosaic of bottom types in thearea is representative of the west coast of New Caledonia (Richer de Forges, 1991). The west coast isdry, annual rainfall at Koumac is approximately800mm, and the study area receives fresh water

essentially from only the Koumac river (average dis-charge is 10m3s-1 between December and April, and~1m3s-1 for the rest of the year). The region has semi-diurnal tides with an amplitude of 1.5m. Fieldworkwas conducted during a period of 1 month in October1993. The area surveyed extends from the coast to theouter slope of the barrier reef, situated at a distanceof 9–12km from the shore. The outer slope of thebarrier drops rapidly to depths of several hundredmeters, but the study was restricted to the depth zonedirectly influenced by light, i.e. 0–120m. The barrieris cut by passes: Passe de Koumac (1km wide) andPasse Deverd (3.5km wide) in the study area, withcanyon walls dropping to 60m. Between the barrierand the mainland extends the lagoon with an averagedepth of 15–20m, dotted with islands and subtidalcoral platforms; the lagoon consists mainly of softbottoms, with a typical sequence (Chevillon, 1992) ofwhite bioclastic sand near the barrier reef to fine mudnear the shore. The shoreline has mangroves, sedi-mentary bays with phanerogam beds, and heads withrocks and coral heads.

SAMPLING EFFORT

The area surveyed covers approximately 295km2 and42 discrete stations were sampled by intertidal collecting, scuba diving and dredging (Table 1). Atevery station, complementary techniques have beendeployed, from hand picking to collecting bottomsample by suction sampling (Fig. 2), brushing stonesand dead coral for epibenthos (Fig. 2A), and breakinghard substrates for endolithic organisms. Suctionsampling is the only efficient approach to sample smallorganisms on hard substrates, but is equally reward-ing on soft bottoms. Special attention was given toassociations between molluscs and various inverte-brates, particularly echinoderms and octocorals.Cephalopods, which require an altogether different setof collecting techniques (trawling, baited traps) andcontribute little to the total mollusc species richness,were not taken into consideration during this study.Sampling at any station was qualitative, and collect-ing effort was proportional to species richness andhabitat heterogeneity as perceived empirically in thefield. For example, an intertidal brackish mangrovehabitat was thought to have been adequately sampledafter 2 day-persons, but a station on the outer slope ofthe barrier reef necessitated 15 day-persons for thesame level of surveying. Total fieldwork amounted to400 day-persons.

TAXONOMIC PROCESSING AND DATA ANALYSIS

Samples were processed fresh by sieving in seawaterand fractioning to size classes to 0.37mm. Fractions

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100 km

Koumac

New Caledonia

5 km

10

10

10

10

20

50

20

Figure 1. Geographical setting of the study area. Hatched area represents the mainland, dotted areas are reefs, includ-ing the barrier reef running NW–SE. Bathymetric contours 10, 20, 50 and 100 meters.

Table 1. Number of stations sampled on different bottom types in the Koumac coral reefs complex. Total area of studysite 295km2

landscape units bottom types extent of bottom type (% of study site) no. of stations

shore mangrove 0.5 1intertidal soft bottoms 2.5 5

hard bottoms and mixed habitats 8 8

coral reef lagoon soft bottoms 75 70–20m hard bottoms 9 6

passes and outer soft bottoms 3 6barrier reef hard bottoms 2 910–120m

larger than 3mm were sorted in totality with thenaked eye. Fractions in the 1–3mm range were sortedin totality with a dissecting microscope. The smallestfractions (0.5 and 0.37mm) were sorted with a dis-secting microscope, but sorting ceased after repeatedsubsamples failed to reveal additional species. At thestudy site, material was simply sorted and preservedin bulk as ‘molluscs’; in addition, nudibranchs andsome other groups with remarkable colour patternswere separated for photography or drawing of livingspecimens. Only living specimens and fresh emptyshells were picked. Empty and imperfect shells werediscarded except when it was uncertain that they represented species already present in the sample. Inthe laboratory, samples from individual stations werefurther sorted to morphospecies or operational taxo-nomic units (OTUs, also referred to as RTUs, recog-nizable taxonomic units, cf. New, 1999). OTUs wereidentified at least to family level but, although gener-ally no attempt was made to identify them at lowertaxonomic levels (genus and species), the taxonomiclimits of our OTUs was verified by a network of tax-onomists (as listed in Appendix 1); in fact, our OTUscorrespond rather closely to what is called a species inthe taxonomical, biogeographical or ecological litera-ture, and in the Results and Discussion sections, ‘OTU’and ‘species’ refer to the same concept.

After the segregation to morphospecies, the follow-ing additional data were captured:

(a) Gross measure of abundance: number of speci-mens, adults and juveniles, alive and dead indiscrim-inately, per species per station.

(b) Size: randomly selected adult specimens of indi-vidual species were measured. Species without shells(essentially nudibranchs, sacoglossans and a few other‘slugs’) were not measured and are excluded from theanalysis of patterns of size distribution.

(c) ‘Live’ vs. ‘dead only’ categories: a species waslisted in the ‘live’ category when at least one specimenhad been taken alive at any station, no attempt wasmade to distinguish between living and non-livingoccurrences at station level. Assigning shelled mol-luscs, especially gastropods, to the mutually exclusive‘live’ or ‘dead only’ categories presents special difficul-ties which can be overcome by stains or breakingshells. However, to permit further use of the materialfor taxonomical studies, we did not attempt to usethese destructive or semidestructive methods; as aresult, a small number of species could not be assignedwith confidence to either category.

The resulting information was displayed in a rela-tional database. Cumulative curves were calculatedwith the EstimateS 5 programme (Colwell, 1999),which computes randomized species accumulation

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Figure 2. Methods deployed to collect small molluscs on hard substrates: suction sampling with a 2 m long aspirator (2 A, left, and 2B) and brushing coral rubble and stones in a box lined with a 0.5mm mesh net.

curves; we ran the programme for 50 random draw-ings of the 42 stations. Size data were analysed usingStatView. All the material of the present study is conserved in Muséum National d’Histoire Naturelle,Paris.

RESULTS

SPECIES RICHNESS

A total of 127652 specimens, representing 2738species of molluscs, were collected at the study site(Table 2; Appendix 2). Among the bivalves, three fam-ilies are represented by 50 species or more, and among

the gastropods four had 100 species or more. The mostspeciose group is the turriform Conoidea (i.e. Conoideasensu Taylor et al., 1993, excluding the genus Conus),with no fewer than 263 species (314 when Conus isincluded).

The cumulation curve (Fig. 3) shows an incrementof 23 species between the penultimate and the last sta-tions. This, in addition to the high number of speciesfound at single stations, or represented by single specimens or only by empty shells, suggests that oursample was not saturated. Projections from the speciescumulation curve all extrapolate the total richness atthe study site to over 3000 species of molluscs: 3358species (Michaelis-Menten equation), 3593 (Jack 1resampling method), 3971 (Jack 2 resamplingmethod), and 3137 (Bootstrap).

SIZE

The adult size of 2581 mollusc species collected at thestudy site was measured, and was found to range from0.4–450mm. As result of this large interval, the meanis 17mm, but the median is 8mm and the mode is only3mm. The largest size class is 1.9–4.1mm among the micromolluscs; 33.5% of the species (864) have an adult size smaller than 4.1mm. By contrast, thepooled classes of macromolluscs (‘seashells’) largerthan 41mm account only for 8% of the total fauna(Fig. 4).

RARITY

Biological rarityThe dominant feature of the abundance-rank rela-tionship (Fig. 5) is the very long tail of rare species. If

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Table 2. Abundance (number of specimens) and number of species for the four higher molluscan taxa and selected fam-ilies of bivalves and gastropods

Taxon 1 Taxon 2 No. specimens No. species

Polyplacophora 201 16Scaphopoda 413 16Bivalvia 45480 519

Galeommatidae 739 60Tellinidae 3560 51Veneridae 5041 53

Gastropoda 81558 2187Cerithiopsidae 1096 99Triphoridae 2839 174Eulimidae 1047 138Turridae s.l. 4732 314Pyramidellidae 2570 132Opisthobranchia 5215 258

Mollusca total 127652 2738

Figure 3. Species cumulation curves based on EstimateS5 (Colwell, 1999); Jackknife (Jack 1, Jack 2) and Bootstraprichness estimators.

19.8% (542 species) are even represented by singlespecimens (Fig. 6A). When the quartile definition ofrarity is followed (Gaston, 1994), all ‘rare’ species inthe study are represented by an average of 1.2 speci-mens. Among the most speciose families, the filter-feeding bivalve families Veneridae and Tellinidae are also numerically abundant (average 87 speci-mens per species). The other speciose families havespecialized feeding habits and are numerically rare(average 14.9 specimens per species). Cerithiopsidaeand Triphoridae feed on sponges, Eulimidae are parasitic on echinoderms, ‘Turridae’ essentially preyon polychaetes, and Galeommatidae and Pyramidel-lidae are parasites or associates of various invertebrates.

Ecological rarityWhen occurrences at individual stations are consid-ered, 32% of the species (876 species) were collected atsingle stations (these include the 542 species repre-sented by single specimens, plus 334 more thatoccurred at single stations but are represented by twospecimens or more), and only 676 are present in morethan five stations (Fig. 6B).

29.8% of the species were not collected alive duringthe survey (Fig. 7A). 51% of these 783 species repre-sented only by empty shells (401 species) arerestricted to single stations, but only 22% of the 1847

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Figure 4. Size structure of the 2581 shelled mollusc species present at the Koumac site, based on randomly selected adultspecimens. The ten size classes have intervals that are equivalent in a logarithm transformation with base 2.

Figure 5. Biological rarity of the marine molluscs fromKoumac, New Caledonia. Rank of the 2738 species using alogarithmic scale of abundance (number of individuals);dashed line delineates those species which under a quar-tile definition are categorized as rare.

the 2738 species were evenly represented in thesample, there would be an average of 46.7 specimensper species. In reality, 48% of the species (1315species) are represented by five specimens or less, and

species collected alive (433 species) are in that situation (Fig. 7B).

DISCUSSION

HOT SPOTS OR COLLECTING SPOTS?

With 2738 species recorded, and 3137–3971 speciespredicted, in a 295-km2 coral reef complex, the molluscspecies richness observed in this study is one order ofmagnitude higher than that reported in the literaturefrom middle latitudes sites of comparable extension,and is several times the mollusc richness reportedfrom other tropical Indo-Pacific sites (Table 3). It isalso comparable (or greater) in magnitude to globalnon-tropical provinces, even when these include an‘offshore’ component that was not measured in thepresent study.

We suggest that three main factors had, separatelyor together, contributed to the underestimation ofactual richness in previous studies:

(1) Inadequate or insufficient coverage of spatialheterogeneity. On a total of 42 stations, 32% of thespecies have been collected at single stations, and

75% at fewer than five stations. A similarly high incidence of ‘ecological endemism’ was found bySchlacher et al. (1998) in the lagoon of Great AstrolabeReef (Fiji). That their study and this study reachsimilar results despite very different samplingapproaches (Schlacher et al., 1998 sampled soft bottommacrofauna by grabs) confirms the classical intuitionthat high spatial heterogeneity in community struc-ture is a feature coral reefs share with rain forests(Reaka-Kudla, 1997).

(2) Inadequate sampling of the very stenoeciousspecies. Many families, including the very specioseones, have species with highly specialized diets, and anumber of these are semisessile or sessile on theirhosts. The existence of such species is revealed only ifthe hosts are appropriately sampled and scrutinized.In parasitic species such as eulimid gastropods withinfestation prevalence usually in the order of 1–20%,this requires collection, and sometimes even dissec-tion, of large suites of echinoderm hosts. Such a spe-cialized approach is never carried out in routine faunalsurveys, which consequently miss the majority of commensals, associates and parasites.

(3) Overemphasis on macromolluscs. Faunal sur-veys and inventories have a tendency to focus on the large species of ‘seashells’ and neglect the smallerspecies. For example, in a Rapid Assessment Surveyof the conservation value of Milne Bay (Papua NewGuinea), Wells (1998) found that the five most speciosefamilies were the Conidae (54 species), Cypraeidae(33), Thaididae (26), Cerithiidae (21), and Veneridae(36); only the latter stands out as a speciose family inour study. In the Koumac study, at least five of theeight most speciose families can be considered micro-molluscs, and many species in the remaining threefamilies are also micromolluscs. We believe that the emphasis on macromolluscs is a perfectly validapproach when limited collecting and sortingresources are available in the field: the faunal assess-ment of Milne Bay by Wells was the result of 19 day-persons in the field, compared with 400 in the presentstudy. In addition, the taxonomy of macromolluscs isrelatively better known; most species can be readilyidentified in the field by an experienced collector, and this may be regarded as a more environmentallyfriendly approach in conservation studies.

To summarize, we believe that there is nothingexceptionnal about the New Caledonia site chosen andour numbers merely reflect the massive collecting andsorting effort involved, followed by the input of a comprehensive network of taxonomists.

HOW ADEQUATELY DOES OUR OWN STUDY APPROACH

THE REAL SPECIES RICHNESS?

Despite the massive collecting and sorting effort of our

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Figure 6. Biological and ecological rarity of the marinemolluscs from Koumac, New Caledonia. Global proportionsof species in three arbitrary abundance (number of speci-mens) categories (A) and 4 arbitrary occurence (number ofstations of occurence) categories (B).

study, it is certain that we did not successfully sampleall the mollusc species living within the perimeter ofthe study site, but how many did we miss?

Some organisms have very seasonal or sporadicoccurences and no survey, whatever its intensity, canapproach a complete coverage of such species ifrestricted to a single period of the year. The seasonal-ity of nudibranchs is well documented in temperatewaters, and there is also evidence that the occurrenceof many tropical species is locally unpredictable (see,e.g. Marshall & Willan, 1999). The number of opistho-branch species found at the Koumac site (258) isremarkably similar to that observed during 18 yearson Heron and Wistari Reef, southern Great BarrierReef (262 species: Marshall & Willan, 1999), but fallsfar short of that found at Madang, Papua New Guinea(561 species: Gosliner, 1992; T. M. Gosliner pers.comm. in Marshall & Willan, 1999) during repeated

surveys over many years. Undoubtedly, the differenceis in part a reflection of the richness gradient in theWest Pacific, as well as a result of a more thoroughcoverage of the Madang opisthobranch fauna. In thesame vein, Mikkelsen & Bieler (2000) found that theirown extensive collecting efforts of bivalves in theFlorida Keys over five years yielded 55% of the speciesrecorded by a combination of museum collections, literature sources and original field work, with theearliest records from the 1870s.

Of the various projections from the cumulationcurve (Fig. 3), Palmer (1990) suggested that the first-order jackknife (Jack 1) estimator is the most preciseand least biased: in the present study, this extrapola-tion stands at 3593 species, i.e. 855 species (31%) morethan we actually collected. However, the very long ‘tail’of very rare species suggests that the result from theJack 2 resampling method (3971 species) may reflect

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Figure 7. Proportion of species represented only by empty shells (A), and their relative ecological abundance contrastedto that of species represented by live-collected specimens (B).

more accurately the actual number of species present, i.e. 1233 species (45%) more than we actuallycollected.

POST MORTEM REMAINS: BACKGROUND NOISE OR

BIODIVERSITY INDICATORS?

Because empty shells can be transported by gravity,water movements or hermit crabs, they are usuallycarefully excluded from ecological studies of speciesdiversity at discrete stations. Indeed, we have noassurance that a species represented only by emptyshells is part of the community at the scale of indi-vidual stations and at the time of collecting. Con-versely, it is customary for regional catalogues to listmollusc species even when all known records arebased on empty shells. In fact, quite a few species ofmolluscs known and described 100 or 200 years agohave never been collected alive, including well-surveyed regions in Europe or North America.

In the present study, species represented only by

empty shells are included because it is highly likelythat they are part of the ecosystem at the spatial scaleof the study site and on a multiseasonal basis. Thehypothesis that such species have been transported for several kilometres from outside the study site isextremely unlikely. Species represented only by emptyshells may not have been collected alive for a numberof possible reasons: they live in a habitat that is diffi-cult to sample (e.g. narrow fissures or cavities in rocks,deep burrowing bivalves); they have a very specializedhabitat (e.g. ovulids associated with individual speciesof octocorals, or eulimids associated with echino-derms); they are exceedingly rare; they live at a seasondifferent from the study period; or several of thesefactors operate together. The difficulty to sample suchspecies leads to a form of rarity termed pseudo-rarityby Gaston (1994). In this respect, it is remarkablethat, among the species that occur at single stations(‘singletons’), 52% are represented only by emptyshells; but this percentage falls to 19.5% for thespecies present in two or more stations (Fig. 7). Empty

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Table 3. The total marine mollusc species richness of selected tropical and world faunas, compared to that of the Koumacsite. The data are not all totally comparable as some lists deal only with material collected on the shore while othersinclude deep-sea offshore faunas to c. 1000 m. Note that in the Indo-Pacific all evaluations of species numbers at localscales relate to oceanic islands

Location Depth range No. species Source

Tropical Indo-Pacific: localKoumac, New Caledonia littoral/sublittoral 2738 This paperKwajalein littoral/sublittoral 1279 Kay (1995)Eniwetak, Marshall Islands littoral/sublittoral 1021 Kay & Scott (1987), Kay (1995)Cocos-Keeling, Indian Ocean littoral 504 Orr Maes (1967)Easter Island littoral 121 Rehder (1980), Kay (1995)

Tropical Indo-Pacific: regionalOkinawa littoral/sublittoral 1853 Kay & Scott (1987)Red Sea littoral to offshore 1733 Dekker & Orlin (2000)Guam and norther Marianas littoral/sublittoral 1139 Kay (1995)Hawaii littoral to offshore 1071 Kay (1995)Society & Tuamotus littoral/sublittoral 959 Kay (1995)Pitcairn group littoral/sublittoral 426 Preece (1995)

Tropical Atlantic: localIndian River, Florida littoral/sublittoral 428 Mikkelsen et al. (1995)Florida Keys littoral/sublittoral 1400 Mikkelsen & Bieler (2000)

Non-tropical Atlantic: local and regionalGarraf, NW Mediterranean littoral to offshore 622 Giribet & Penas (1997)Plymouth, UK littoral/sublittoral 375 Anonymous (1957)White Sea littoral/sublittoral 162 Scarlato (1987)

Global provinces (non-tropical)South Africa littoral to offshore 2788 Kilburn & Herbert (1999)Mediterranean littoral to offshore 2024 Sabelli et al. (1990)New Zealand littoral to offshore 2091 Spencer & Willan (1996)

shells thus appear to represent an extreme scenario ofrarity. Rather than background noise to be discarded,we view empty shells as a biodiversity indicator thatpoints to the difficulty of estimating the real magni-tude of species richness for taxonomical groups that donot leave post mortem remains, such as polychaetes,meiofauna, peracarid crustaceans, etc.

IMPLICATIONS FOR GLOBAL

TAXONOMIC INVENTORYING

Marine environments are still incompletely invento-ried and new species continue to be described at a paceof c. 1800 species per year (unpubl. data based on asurvey of Zoological Record for Animals and AquaticSciences & Fisheries Abstract for ‘algae’ and fungi,study period 1992–97). For marine molluscs, approxi-mately 75% of the newly described species are fromthe tropics, with the Indo-Pacific alone accounting for 43% of a total yearly increment of 280 species(Bouchet, 1997). Even when taking into account a syn-onymy ratio of 1.6 (Solow et al., 1995), the gap betweendescribed and expected global marine species diversityappears to remain unbridgeable in the foreseeablefuture. Gosliner & Draheim (1996) found that 30% of 3400 Indo-Pacific species of opisthobranchs areundescribed.

Because our approach was deliberately limited tosegregating morphospecies without any generalizedattempt to put names on the OTUs, we cannot suggestwhat proportion of the total mollusc fauna found inKoumac is undescribed. Superficial examination ofsuch speciose families as the Turridae, Eulimidae,Triphoridae and Cerithiopsidae suggests that numer-ous new species are present, perhaps up to 80% in thecase of Eulimidae (A. Warén, pers. com.). Scatterednew species have already been described based onmaterial collected at Koumac (Rudman, 1995; Dijkstra& Southgate, 2000; Houart, 2001), but the total prob-ably amounts to several hundred new species.

FROM LOCAL TO GLOBAL PERSPECTIVES:SPECULATING FROM KOUMAC TO THE WHOLE

INDO-PACIFIC

In their now classical work on small macrofaunalinvertebrates from the northwest Atlantic deep-sea,Grassle & Maciolek (1992) established a model ofspatial correlation between the number of species andgeographical distance along a transect, and estimatedthat one additional species was gained every km ofocean bottom. From this approach, they projected thatthe 626 species they observed in 21 m2 could projectinto 10 million species of deep-sea small macrofaunalinvertebrates in the world ocean. At the opposite ofthis approach, Fenchel et al. (1997), based on a study

of ciliates from two European sites, concluded that the global richness of microorganisms has no spatialdimension, and that ‘everything is everywhere’ (butsee Lee & Patterson, 1999).

Clearly, the spatial correlates of global marine bio-diversity are still poorly understood, and we currentlyhave no idea as to how the 3000–3500 species of mol-luscs present on 295km2 at the Koumac site could possibly predict the global mollusc richness in the c.10.106 km2 of the whole Indo-Pacific. To illustrate themargin of error of such projections, comparisons canbe made between local inventory at Koumac and thetotal Indo-Pacific for two globally well inventoriedfamilies of macrogastropods, the Cypraeidae (cowries)and the Volutidae (volutes). Cowries generally haveplanktotrophic larvae and many species have broadIndo-Pacific distributions, whereas volutes have non-planktotrophic development and most have highlylocalized distributions. Of a total of 144 coastal Indo-Pacific species of cowries, 79 (55%) are known fromNew Caledonia (Lorenz & Hubert, 2000), of which 33(23%) were found in Koumac; of a total of 73 coastalIndo-Pacific species of volutes, three (4.1%) are knownfrom mainland New Caledonia (Poppe & Goto, 1992;with additions), of which two (2.7%) were found inKoumac. If these proportions are applied to the 2738species actually recorded in Koumac, the total numberof coastal species of molluscs in the near-shore Indo-Pacific would be somewhere between 11 904 (projec-tion based on cowries) and 99 963 species (based onvolutes).

Two other south-west Pacific sites sampled with asimilar collecting effort (Touho, on the east coast ofNew Caledonia, and Baie du Santal, in the LoyaltyIslands) are currently being processed and analysed.We expect that the results should shed light on thespatial component of biodiversity, admittedly the mostcrucial step in estimating global species richness (Ødegaard, 2000).

ACKNOWLEDGEMENTS

Our work in New Caledonia was made possiblethrough the logistics of Institut de Recherche pourDéveloppement (IRD, formerly ORSTOM) and Aquar-ium de Nouméa, and we would like to thank its thendirectors, respectively, F. Jarrige and P. Joannot, themayor of Koumac and elders of the Ouanap tribe forpermission and facilities, and our colleagues B. Richerde Forges, J. Chazeau, P. Cayré for encouragementand support. Our thanks extend to J. L. Menou, G.Bargibant, P. Scaps, R. Hintz, P. Rual Jr, and manyothers for assistance in the field, and to the taxono-mists enumerated in Appendix 1 for their participa-tion in species separation.

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APPENDIX 1

Taxonomists who assisted in the present study by sorting material to OTUs or verifying our partitioning.A. Beu (Tonnoidea), R. Bieler (Architectonicidae, Mathildidae), G. Coovert (Marginellidae, Cystiscidae), R. von

Cosel (Solenidae, Pharidae, Solecurtidae), H. Dijkstra (Pectinoidea), L. Dolin (Cypraeidae, Triviidae), E. Glover(Lucinidae), S. Gofas (Neoleptonidae), R. Houart (Muricidae), A. Le Goff (Epitoniidae, Triphoridae, ‘Turridae’),B. Marshall (Patellogastropoda, Tricoliidae, Phenacolepadidae, Cingulopsidae, Truncatellidae, Assimineidae,Barleeiidae, Anabathronidae, Iravadiidae, Elachisinidae, Litiopidae, Scaliolidae, Calyptraeidae, Trichotropidae,Cerithiopsidae, Triphoridae, Epitoniidae, ‘Turridae’, Cornirostridae, Rissoellidae, Amathinidae, Archaeopul-monata), A. Matsukuma (Mytilidae, Tellinidae), J. McLean (Liotiinae), P. Mikkelsen (Juliidae), M. Pizzini (Caecidae), M. Poulicek (Hipponicidae, Capulidae), J. M. Poutiers (Fimbriidae, Tridacnidae, Veneridae, Petricolidae, Spheniopsidae, Cuspidariidae, Pholadidae), G. Rosenberg (Ovulidae), W. Rudman (Opistho-branchia), F. Scarabino (Columbellidae), V. Scarabino (Scaphopoda), S. Schiaparelli (Siliquariidae, Vermiculari-inae, Vermetidae), H. Strack (Polyplacophora), J. Taylor (Lucinidae), J. Trondle (Trochidae, Neritidae,Littorinidae, Cerithiidae, Dialidae, Naticidae, Nassariidae, Harpidae, Costellariidae, Mitridae, Olividae,Conidae, Terebridae), A. Verhecken (Cancellariidae), J. Vidal (Cardiidae), A. Warén (Eulimidae).

APPENDIX 2

List of families collected on the Koumac site. Sequence follows commonly accepted systematics. For each family,the first column gives the total number of species, the last column gives the total number of specimens. Totalnumber of species is subdivided into: species represented by living specimens (column 2), species representedonly by empty shells (column 3), and species that could not be allocated to one of these two categories (column4).

Total number Number ofof species Living species Empty shells only Status doubtful specimens

POLYPLACOPHORALepidopleuridae 1 1 0 0 5Ischnochitonidae 4 4 0 0 49Mopaliidae 1 1 0 0 11Chitonidae 5 5 0 0 81Acanthochitonidae 4 4 0 0 17Cryptoplacidae 1 1 0 0 38

SCAPHOPODADentaliidae 16 9 7 0 413

BIVALVIANuculidae 1 1 0 0 2015Nuculanidae 1 0 1 0 20Arcidae 24 12 12 0 2737Cucullaeidae 1 0 1 0 12Noetiidae 5 3 2 0 1676Glycymerididae 3 2 1 0 1701Philobryidae 1 1 0 0 200Mytilidae 27 26 1 0 4582Pinnidae 3 3 0 0 47Pteriidae 12 12 0 0 246Isognomonidae 4 4 0 0 499Malleidae 3 3 0 0 162Propeamussiidae 5 5 0 0 606Entoliidae 1 0 1 0 7Pectinidae 27 20 7 0 1915Plicatulidae 2 1 1 0 91Spondylidae 16 8 8 0 187Dimyidae 1 1 0 0 15Anomiidae 6 2 4 0 75Limidae 15 8 7 0 846Ostreidae 9 7 2 0 273Lucinidae 20 11 9 0 1280Ungulinidae 5 3 2 0 473Fimbriidae 1 1 0 0 90Chamidae 9 6 3 0 197Montacutidae 1 0 1 0 1Galeommatidae 60 23 37 0 739Carditidae 7 7 0 0 1722Condylocardiidae 1 1 0 0 10Crassatellidae 1 0 1 0 7Cardiidae 34 32 2 0 4316Tridacnidae 3 3 0 0 12Mactridae 11 7 4 0 677Mesodesmatidae 8 6 2 0 1654Solenidae 2 2 0 0 332Pharidae 2 1 1 0 33Tellinidae 51 32 19 0 3560Psammobiidae 13 10 3 0 907Donacidae 2 2 0 0 944Semelidae 19 12 7 0 1282Solecurtidae 3 1 2 0 64Kelliellidae 1 0 1 0 5Trapeziidae 4 2 2 0 66Glossidae 1 0 1 0 3Corbiculidae 1 1 0 0 21Veneridae 53 38 15 0 5041Neoleptonidae 1 1 0 0 1904Petricolidae 3 1 2 0 44Myidae 2 1 1 0 4Corbulidae 3 3 0 0 813Spheniopsidae 1 1 0 0 184Gastrochaenidae 7 5 2 0 79Hiatellidae 1 1 0 0 163Cleidothaeridae 1 1 0 0 4Laternulidae 1 1 0 0 4Lyonsiidae 1 0 1 0 3Myochamidae 2 2 0 0 550

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Thraciidae 6 2 4 0 185Cuspidariidae 5 2 3 0 65Clavagellidae 1 1 0 0 3Pholadidae 3 1 2 0 108Pandoridae 1 1 0 0 19

GASTROPODAPatellidae 2 2 0 0 5Lepetidae 1 0 1 0 1Nacellidae 4 3 1 0 264Haliotidae 7 3 4 0 50Scissurellidae 11 9 2 0 834Fissurellidae 34 19 15 0 793Trochidae 56 43 10 3 4241Turbinidae 15 13 1 1 2126Skeneidae 13 7 6 0 665Phasianellidae 1 1 0 0 4318Neritopsidae 1 0 1 0 6Neritidae 14 12 2 0 2489Phenacolepadidae 6 1 5 0 23Littorinidae 7 7 0 0 709Cingulopsidae 1 1 0 0 24Truncatellidae 1 0 1 0 4Assimineidae 1 0 1 0 12Rissoidae 60 27 6 27 3023Barleeiidae 11 10 1 0 6802Anabathronidae 1 1 0 0 1589Adeorbidae 22 7 15 0 272Caecidae 13 6 7 0 168Iravadiidae 2 1 1 0 6Elachisinidae 1 0 1 0 2Planaxidae 2 1 1 0 208Fossaridae 3 1 2 0 10Modulidae 1 1 0 0 6Cerithiidae 42 33 9 0 5818Litiopidae 3 2 1 0 785Scaliolidae 7 5 2 0 2983Dialidae 3 3 0 0 3453Potamididae 1 1 0 0 16Siliquariidae 5 0 0 5 19Turritellidae 7 5 2 0 1645Vermetidae 4 0 0 4 9Plesiotrochidae 2 2 0 0 810Strombidae 19 15 4 0 864Calyptraeidae 5 4 1 0 51Vanikoridae 10 3 7 0 180Hipponicidae 8 5 3 0 202Capulidae 1 1 0 0 3Trichotropidae 4 0 4 0 8Xenophoridae 2 2 0 0 16Cypraeidae 32 24 8 0 329Ovulidae 28 22 6 0 347Triviidae 17 16 1 0 643Lamellariidae 2 2 0 0 2Naticidae 29 24 5 0 926Cassidae 5 5 0 0 44Bursidae 7 7 0 0 112Ranellidae 20 17 3 0 211

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Personidae 4 3 1 0 28Ficidae 1 0 1 0 1Cerithiopsidae 99 35 33 31 1096Triphoridae 174 98 70 6 2839Epitoniidae 46 24 22 0 763Aclididae 6 6 0 0 17Eulimidae 138 89 49 0 1047Muricidae 62 51 11 0 1695Coralliophilidae 14 6 8 0 58Buccinidae 29 20 8 1 638Nassariidae 32 23 9 0 1441Fasciolariidae 16 14 2 0 333Colubrariidae 3 0 2 1 8Columbellidae 45 33 12 0 3694Volutidae 2 2 0 0 23Turbinellidae 1 1 0 0 22Harpidae 4 2 2 0 8Marginellidae 6 4 2 0 192Cystiscidae 20 17 3 0 1745Costellariidae 71 52 17 2 1788Mitridae 56 41 14 1 356Olividae 5 5 0 0 226Cancellariidae 5 3 2 0 137Turridae (s.l. excl. Conus) 263 154 102 7 4196Conidae 51 43 6 2 536Terebridae 38 36 2 0 1094Cornirostridae 6 4 2 0 17Orbitestellidae 5 4 0 1 67Architectonicidae 13 0 0 13 67Mathildidae 3 0 0 3 45Rissoellidae 6 5 1 0 704Omalogyridae 3 3 0 0 37Pyramidellidae 132 83 49 0 2570Amathinidae 1 0 1 0 36Ebalidae 2 2 0 0 39Acteonidae 12 9 3 0 442Diaphanidae 1 1 0 0 1Ringiculidae 4 3 1 0 323Philinidae 2 2 0 0 2Bullidae 56 33 23 0 3099Bullinidae 3 0 3 0 13Hydatinidae 1 1 0 0 3Haminoeidae 4 4 0 0 380Juliidae 3 3 0 0 421Umbraculidae 1 1 0 0 1Aplysiidae 9 9 0 0 20Aegiretidae 3 3 0 0 3Aeolidiidae 4 4 0 0 4Aglajidae 10 10 0 0 53Akeridae 1 1 0 0 9Arminidae 1 1 0 0 14Bornellidae 1 1 0 0 1Chromodorididae 34 34 0 0 118Costasiellidae 1 1 0 0 1Dendrodorididae 8 8 0 0 19Dorididae 28 28 0 0 57Dotidae 1 1 0 0 1Elysiidae 9 9 0 0 27

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Embletoniidae 1 1 0 0 1Eubranchidae 1 1 0 0 4Flabellinidae 2 2 0 0 3Gastropteridae 5 5 0 0 9Glaucidae 7 7 0 0 24Gymnodorididae 12 12 0 0 23Hancockiidae 1 1 0 0 1Lomanotidae 1 1 0 0 1Madrellidae 1 1 0 0 10Onchidorididae 1 1 0 0 20Phyllidiidae 8 8 0 0 20Pleurobranchidae 4 4 0 0 17Polybranchiidae 3 3 0 0 4Polyceridae 4 4 0 0 9Stiligeridae 1 1 0 0 1Tergipedidae 4 4 0 0 31Tethydidae 3 3 0 0 22Tritoniidae 2 2 0 0 3Siphonariidae 4 4 0 0 266Ellobiidae 9 9 0 0 388Total 2738 1847 783 108 127652

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