Subfossil Land Snail Fauna (Mollusca) of Central Chichijima, Ogasawara Islands, with Description of a New Species1

Satoshi Chiba,2,3 Tetsuro Sasaki,4 Hajime Suzuki,4 and Kazuo Horikoshi4

Abstract: The fossil record provides useful information to estimate what island communities were like before human colonization. We examined the species composition of the subfossil land snail fauna of dune deposits at the Yatsuse River, central Chichijima, Ogasawara Islands, and compared it with the species recorded in Chichijima since the nineteenth century. The 22 species in the dune deposits included 13 species that are now extinct in Chichijima. Live specimens of 11 of these extinct species were recorded in the early twentieth century, but no living Mandarna pallasiana and Ogasawarana obtusa Chiba et al., n. sp., have ever been recorded. Age of the sediment, estimated by radiocarbon (14C) dating, was 720 years B.P., and it is possible that these two land snail species became extinct as a result of the impact of human colonization of the island, which started in 1830. Specifically, Ogasawarana obtusa, n. sp., became extinct before the start of taxonomic studies of the land snails of Ogasawara. The sample included Hawaiia minuscula, which is generally now considered a cosmopolitan species introduced from North America. This finding suggests that Hawaiia minuscula is not alien in Ogasawara but indigenous.

Recent palaeontological research has snail faunas are often preserved as fossils in shown that prehistoric human activity is a sediments, making it relatively easy to infer major cause of degradation of island ecosys- how species have gone extinct as a result of tems ( James et al. 1987, Hotchkiss and Juvik human activity (Christensen and Kirch 1986, 1999, Burney et al. 2001). It is important to Cook et al. 1993, Goodfriend et al. 1994, know how communities and ecosystems were Cameron and Cook 1996, Preece 1998, changed by initial human colonization. Land Cowie and Grant-Mackie 2004). snails of islands provide excellent model sys- The Ogasawara Archipelago in the north- tems to investigate the impacts of human western Pacific harbored approximately 100 colonization on communities, because serious native land snail species, 90% of which were extinctions have been recorded on a number endemic (Kuroda 1930, Habe 1969, Kuro- of islands and because the prehistoric land zumi 1988, Tomiyama and Kurozumi 1991). On Chichijima, the largest island, 51 species have been described and more than 50% 1 This study was conducted under permits from the of these are thought to have been lost Agency for Cultural Affairs (No. 4-1555) and the South Kanto branch, Ministry of the Environment (No. (Tomiyama and Kurozumi 1991). Two species 050815001) and was supported by the Global Environ- of land snails from Ogasawara were first mental Research Fund (F-051). Manuscript accepted collected on a voyage by Captain Frederick 5 April 2007. Beechey in 1827 (Mandarina mandarina and 2 Corresponding author (e-mail: [email protected] Mandarina luhuana), and most of the land .ne.jp). 3 Graduate School of Life Sciences, Tohoku Univer- snail species of Ogasawara were described by sity, Aobayama, Sendai 980-8578, Japan. H. A. Pilsbry and Y. Hirase in the early twen- 4 Institute of Boninology, Chichijima-Aza- tieth century. However, human colonization Miyanohamamichi, Ogasawara, Tokyo 100-2101, Japan. of Ogasawara began in 1830 with seven im- migrants from Hawai‘i, and it is not known Pacific Science (2008), vol. 62, no. 1:137–145 what the land snail community of Ogasawara : 2008 by University of Hawai‘i Press was like before human colonization and how All rights reserved this initial human colonization affected the

137 138 PACIFIC SCIENCE . January 2008 native land snail fauna. Because details of the rated from the block using a sieve. The sam- history of human colonization of Ogasawara ples used for this study were deposited at the were recorded in a number of historical Institute of Boninology (Chichijima-Aza- documents, fossil materials from before hu- Miyanohamamichi, Ogasawara [CIBML]). man colonization may provide useful infor- mation for understanding the process of Dating of the Subfossil Sample extinction caused by human activity. In this study, we examined the species The age of the subfossil shells was deter- composition of the subfossil land snail fauna mined by radiocarbon (14C) dating at the of dune deposits in the central part of Chi- Geo-Science Laboratory Co., Ltd (Ueda, chijima to characterize the composition of Tenpaku-ku, Nagoya) and the Institute of the land snail fauna of Ogasawara before the Accelerater Analysis, Ltd. (IAA) (Nobori- first human colonization. We compare the toshinmachi, Tamaku, Kawasaki). The mate- species composition of the subfossil fauna rials used for radiocarbon dating were all land with that of the fauna recorded since the snail shells. The radiocarbon date was cor- early nineteenth century and discuss the im- rected for isotopic fractionation (Goodfriend pact of the first human colonization on the and Stipp 1983), and its bulk date was based native land snail fauna of Ogasawara. In addi- on a pooled sample of Mandarina chichiji- tion, based on the occurrence of subfossil mana. The calendar calibration was calculated species, we show that a species formerly pro- using the newest calibration data (Reimer et posed as an alien species is indigenous. al. 2004) and using the mathematical cubic spline fit (Talma and Vogal 1993). An anom- aly of 14C in the snail shell has been reported materials and methods (Goodfriend and Stipp 1983), and it is one of the problems in 14C analysis of the fossil Samples samples. To check the error due to the age Subfossil land snails were found in Holocene anomaly, the 14C age of the shells of living dune deposits that were uncovered at a snails of M. chichijimana was determined. dredging site on the Yatsuse River at Kitafu- kurozawa, in central Chichijima (Figure 1). Identification The deposits consist of fine to coarse sand and include lenses of silt. The uppermost Each subfossil shell was identified to species, parts of the deposits are covered by silt and and numbers of shells of each species found soil. The base of the sand layer remains in the block were recorded. The occurrence buried. This sampling site is 1 km inland of species in the subfossil samples was com- from the coast, and no dunes are now present pared with previous records of land snail spe- at the site. However, it was formerly near the cies in Ogasawara (Kuroda 1930, Habe 1969, beach and coastal dunes because the deposits Tomiyama and Kurozumi 1991). Museum include a number of fragments of corals and collections of Ogasawara land snails (Univer- Foraminifera. The Yatsuse River may have sity Museum, University of Kyoto; Yokosuka been a narrow bay, with the coastal dune City Museum; National Science Museum, around it. Tokyo; Academy of Natural Sciences of Phil- The subfossil land snail shells were dis- adelphia) were also used to assist identifica- tributed in a slightly calcareous sand layer tion. approximately 50 cm thick (Figure 1). We se- lected the part of the deposits in which the results land snail shells are the most abundant, and a 30 by 30 by 50 cm block was excavated from a The 14C age obtained for the subfossil sample position deeper than 10 cm from the deposit was 720 G 70 yr B.P. The real (calibrated) surface to avoid contamination with modern calender age of the sample was 550–780 yr snail shells. The subfossil shells were sepa- B.P. No age anomaly was detected in the Figure 1. A map of Chichijima of the Ogasawara Islands, showing the location of the study site, and a diagrammatic cross section of the study site. 140 PACIFIC SCIENCE . January 2008

TABLE 1 Species Found in the Subfossil Sample, with Their Current Status in Chichijima and Ogasawara, and Whether They Are Endemic or Nonendemic to Ogasawara

Status in Status in Species Collection No. n Chichijima Ogasawara Endemicity

Ogasawarana discrepans Pilsbry CIBML2007001 15 Living Living Endemic Ogasawarana obtusa, n. sp CIBML2007002–003 3 Extinct Extinct Endemic Paludinella minima Habe CIBML2007004 13 Living Living Endemic Lamellidea ogasawarana Pilsbry & Cook CIBML2007005 7 Living Living Endemic Lamellidea nakadai Pilsbry & Hirase CIBML2007006 9 Extinct Extinct Endemic Elasmias kitaiwojimanum Pilsbry & Hirase CIBML2007007 2 Extinct Living Endemic Gastrocopta ogasawarana Pilsbry CIBML2007008 2 Extinct Living Endemic Gastrocopa boninensis Pilsbry CIBML2007009 3 Living Living Endemic Boninena callistoderma Pilsbry CIBML20070010 3 Extinct Living Endemic Hirasea chichijimana Pilsbry & Hirase CIBML20070011 1 Extinct Living Endemic Hirasea diplomphalus Pilsbry & Hirase CIBML20070012 2 Extinct Living Endemic Hirasea operculina Gould CIBML20070013 2 Extinct Living Endemic Hirasea goniobasis Pilsbry & Hirase CIBML20070014 14 Extinct Extinct Endemic Hirasea hypolia Pilsbry CIBML20070015 1 Extinct Extinct Endemic Liardetia boninensis Pilsbry & Hirase CIBML20070016 2 Living Living Endemic Lamprocystis hahajimana Pilsbry CIBML20070017 7 Extinct Living Endemic Vitrinula chichijimana Pilsbry & Hirase CIBML20070018 1 Extinct Extinct Endemic Hawaiia minuscula Binny CIBML20070019–20 7 Living Living Cosmopolitan Boninosuccinea punctulispira Pilsbry CIBML20070021 1 Extinct Living Endemic Mandarina chichijimana Chiba CIBML20070022 18 Living Living Endemic Mandarina hirasei Pilsbry CIBML20070023 2 Living Living Endemic Mandarina pallasiana Pfeiffer CIBML20070024 12 Extinct Extinct Endemic analysis of modern Mandarina shells. Thus, sawara. The sample included a large species, this fossil sample represents the land snail Mandarina pallasiana, previously suggested to fauna of this part of Chichijima a few hun- be a fossil of the latest Pleistocene or early dred years before the first human coloniza- Holocene. The age of the subfossil sample tion of Ogasawara and exemplifies the land showed, however, that the extinction of this snail fauna of Chichijima just before human species was fairly recent, although also before colonization. studies of the land snail fauna of Ogasawara In total, 22 subfossil land snail species were began. identified (Table 1), representing approxi- All the species in the sample were endemic mately 40% of the species previously re- to Ogasawara except one, Hawaiia minuscula corded in Chichijima. Among these subfossil (Figure 2). This species was previously be- species, 21 have been recorded since the lieved to have been an introduced species. nineteenth century, but 13 are now extinct in However, its occurrence in the subfossil sam- Chichijima. Live specimens of 11 of these ple indicates that it is not an alien but is in- extinct species were recorded in the early digenous to Ogasawara. twentieth century. We found one subfossil species of Ogasa- discussion warana, a helicinid genus endemic to Ogasa- wara, which has a shell morphology distinct The subfossil land snails occurring at the from any species of Ogasawarana previously Yatsuse River site provide an insight into how recorded. This species was not recorded in the land snail fauna of Ogasawara changed any previous studies and is not found in any during the initial stages of human coloniza- museum collections. It was extinct before tion. At least two species became extinct malacologists studied the land snails of Oga- in Chichijima before taxonomic studies of Subfossil Land Snail Fauna . Chiba et al. 141

Figure 2. Hawaiia minuscula (CIBML2007002). A, apical view; B, abapical view; C, side view. Scale bar ¼ 1 mm.

Ogasawara land snails began. This extinction sible cause of the extinction. Although a stone is most likely to have resulted from earlier artifact that was assumed to be of prehistoric human colonization in the early nineteenth period was found in Chichijima (Oda 1981) century, because major climatic change that and humans may have visited Chichijima could induce extinction of more than three before the nineteenth century, there is no species is difficult to imagine in Ogasawara evidence of prehistoric human settlement in during 700–200 yr B.P. The first colonizers Ogasawara except for the Kazan Islands (Oda and occasional visitors to Ogasawara in the 1990). Thus, it is most likely that the extinc- early nineteenth century brought goats, pigs, tion of these species occurred during the cats, and dogs to Chichijima (Hawks 1856), nineteenth century. and predation or habitat degradation by the The fossil record suggests that no more introduced animals might have caused the ex- than 20 species previously coexisted at this lo- tinction of these land snail species. In addi- cality in Chichijima. There are no localities tion, the forests of Chichijima were entirely where more than 20 species coexist in the cut down before the early twentieth century modern Ogasawara Islands except on Ani- by immigrants from Japan who colonized jima, where no cultivation has occurred and after 1876 (Funakoshi 1992), so habitat loss the original habitats have been preserved. before the twentieth century is another plau- Fewer than 10 species currently coexist in 142 PACIFIC SCIENCE . January 2008 the same locality (within 100 m2) in Chichi- lieved that Hawaiia minuscula was introduced jima. This suggests that the impact of human from North America to Asia, Europe, and activity on the native land snail fauna has ex- the Pacific region by human transportation. tended over the entire island. Alternatively, However, the finding of Hawaiia minuscula the high species diversity in the fossil sample in deposits from 700 yr ago implies that this might be a result of mixing with older fossils species was already present in Ogasawara that were reworked from lower horizons. If before European colonization of the New faunal composition was changing as a result World. It is unlikely that this species colo- of climatic changes during the Holocene, nized Ogasawara from the New World before mixing of fossil samples of different ages human colonization. This species is indige- could appear to increase species richness nous to North America, because a number in the sample. Although details of climatic of studies document presence of the fossils change in Ogasawara are not known, it is un- of this species in North America since at least likely that the climate during the Holocene the late Tertiary (Schultz and Cheatum 1970, changed so much that faunal composition Miller and Eshelman 1985). Hence, it is most changed, because the climate of these sub- likely that populations of Hawaiia minuscula tropical oceanic islands would be much more in eastern Asia, as well as those in Ogasawara, stable than that of continental temperate re- were not introduced from the New World by gions. Another possibility is that mixing of human activity but are indigenous. Because the shells was the result of their being trans- there is not enough information on the ported from elsewhere. If species composi- fossil land snails of eastern Asia, phylogenetic tion differed among areas and shells were and biogeographical studies using molecular transported from distant areas and mixed markers are needed to confirm this sugges- after the death of the snails, then species tion. Although further studies are needed, richness in the sample would appear higher these findings suggest that populations of than it actually was in the naturally occurring Hawaiia minuscula in the Pacific Islands have fauna. Small and thin-shelled species cannot complex origins and a complex history of be transported long distances without break- immigration: they could be mixtures of in- ing. Because the shells of species with very digenous populations and nonindigenous thin shells, such as species of Hirasea and populations with different origins. Lamprocystis, are not fragmented in the sam- ples, they were not moved long distances, even if they were transported from elsewhere. systematic description The presence in the fossil sample of a Order Neritopsina Cox & Knight, 1960 species with no records since the nineteenth Family Helicinidae Fe´russac, 1822 century and a species possessing a unique Genus Ogasawarana Wagner, 1905 morphology suggests that the land snail fauna of Ogasawara before human colonization Type species: Ogasawarana ogasawarana may have included a number of species phy- (Pilsbry, 1902) logenetically and morphologically distantly related to the species recorded after human Ogasawarana obtusa Chiba, Sasaki, Suzuki & colonization, when taxonomists began to Horikoshi, n. sp. study the Ogasawara land snail fauna. Hence, Figures 3A,B,C investigation of the Holocene fossil sequence is important for our understanding of the di- diagnosis: Shell flat for the genus with versity of the original fauna and how human about 3.5 whorls, a large body whorl, rounded activity affected it. The subfossil sample in- periphery, smooth surface and a large, ellipti- cludes the species Hawaiia minuscula, which cal aperture. formerly was considered as an alien species description: Shell medium in size for introduced from elsewhere to Ogasawara be- the genus, about 3.5 expanding whorls. Spire fore the early twentieth century. It was be- depressed, with height/diameter ratio about Figure 3. Ogasawarana obtusa Chiba et al., n. sp. (CIBML20070019). A, apical view; B, abapical view; C, side view; D, Ogasawarana capsula (Pilsbry, 1902); E, Ogasawarana comes (Wagner, 1905); F, Ogasawarana nitida Minato, 1980. Scale bar ¼ 1 mm. 144 PACIFIC SCIENCE . January 2008

0.55. Sutures shallow, slightly convex, whorls M. Burney, D. McCloskey, D. Kikuchi, adpressed. Body whorl large relative to spire, F. V. Grady, R. Gage II, and R. Nishek. broadly rounded with no peripheral angu- 2001. Fossil evidence for a diverse biota larity. Shell surface very smooth, with fine from Kaua‘i and its transformation since growth lines but no spiral lines. Aperture human arrival. Ecol. Monogr. 71:615–641. large, oval, outer lip expanded with beveled Cameron, R. A. D., and L. M. Cook. 1996. thickening behind reflected margin. Umbili- Diversity and durability: Responses of the cus closed by solid callus pad. Shell diameter Madeiran and Porto-Santan snail faunas 4.9–5.3 mm. Shell height 2.7–2.8 mm. to natural and human-induced environ- material examined: Holotype, CIBML mental change. Am. Malacol. Bull. 12:3– 2007002. Paratypes ðn ¼ 2Þ, CIBML 12. 2007003. Type locality: Kitafukurozawa, Christensen, C. C., and P. V. Kirch. 1986. Chichijima, Ogasawara; Holocene, 720 yr Nonmarine molluscs and ecological B.P. change at Barbers Point, O‘ahu, Hawai‘i. discussion: Among the 14 species of Bishop Mus. Occas. Pap. 26:52–80. Ogasawarana described since the early twen- Cook, L. M., G. A. Goodfriend, and R. A. D. tieth century, the only species having a shell Cameron. 1993. Changes in the land snail with a smooth surface, no spiral lines, and no fauna of eastern Madeira during the Qua- peripheral angularity are O. nitida, O. comes, ternary. Philos. Trans. R. Soc. Lond. B and O. capsula (Minato 1980) (Figure 3). Oga- Biol. Sci. 339:83–103. sawarana obtusa differs from O. nitida in hav- Cowie, R. H., and J. A. Grant-Mackie. 2004. ing a larger and thicker shell with a relatively Land snail fauna of Me´ Aure´ Cave larger body whorl and aperture. Ogasawarana (WMD007), Moindou, New Caledonia: obtusa differs from O. comes in having a much Human introductions and faunal change. larger and flatter shell, with a relatively larger Pac. Sci. 58:447–460. body whorl and aperture. In addition, the Cox, L. R., and L. B. Knight. 1960. Subor- outer lip of O. comes is much thicker than ders of Archeogastropods. J. Malacol. Soc. that of O. obtusa. Ogasawarana capsula has a Lond. 33:17–18. conical shell with a very high spire, and its Fe´russac, A. E. J. P. J. F. d’A. de. 1822. Tab- shape is very different from that of O. obtusa. leaux syste´matiques des animaux mollus- The new species described here has been ques classe´s en familles naturelles, dans overlooked in the study of land snails in lesquels on a e´tabli la concordance de tous Ogasawara, because it probably went extinct les syste`mes; suivis d’un prodrome ge´ne´r- in Chichijima before the start of taxonomic ale pour tous les mollusques terrestres ou studies of the land snails of Ogasawara. fluviatiles, vivants ou fossiles. Deuxie`me partie. (Premie`re section.) Tableaux par- acknowledgments ticuliers des mollusques terrestres et fluvia- tiles, pre´sentant pour chaque famille les We express our sincere thanks to Hideaki genres et espe`ces qui la composent. Classe Takano, Harumi Horikoshi, Naoko Suzuki, des gaste´ropodes. Ordre des pulmone´s Chikako Takahashi, Tomohiro Deguchi, sans opercules. I. Tableau syste´matique de Hayato Chiba, Hideaki Mori, the Ogasawara la famille des Limaces, Limaces, servant branch of the Tokyo Metropolitan Office, de supple´ment provisoire a notre histoire and the Education Committee of Ogasawara naturelle de ces animaux des mollusques Village for assistance with this survey, and to terrestres et fluviatiles, pre´sentant pour Robert H. Cowie for helpful advice. chaque famille les genres et espe`ces qui la composent. A. Bertrand, Paris; J. B. Literature Cited Sowerby, London. Funakoshi, M. 1992. History of development Burney, D. A., H. F. James, L. P. Burney, and destruction. Pages 38–45 in The S. L. Olson, W. Kikuchi, W. L. Wagner, Ogasawara Natural Environmental Study Subfossil Land Snail Fauna . Chiba et al. 145

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