Land Snails of Little Barrier Island, by A.P. Ballance

TANE 28, 1982 LAND SNAILS OF LITTLE BARRIER ISLAND

by A.P. Ballance

Department of Zoology, University of Auckland, Private Bag, Auckland SUMMARY A total of 40 species of native land snails and 1 introduced species were collected from Little Barrier Island. Twenty-one of these species were previously unrecorded on the island, bringing the list of species to a total of 59. The number of snails collected at each site was found to be significantly affected by the moisture content of the leaf litter, with fewer individuals being found as litter moisture increased.

INTRODUCTION

Work on the land snails of Little Barrier Island was carried out during the Auckland University Field Club's scientific trip from 17 August to 26 August 1981. Little Barrier Island (Hauturu) lies 24 kilometres off Leigh, 80 kilometres north of Auckland city, has an area of 2 817 hectares and rises to a height of 722 metres. It was declared a bird sanctuary in 1894 and is now a flora and fauna reserve administered by the Hauraki Gulf Maritime Park Board. Previous work on Little Barrier Island's land snails has been published by Milligan and Sumich (1953). The collection of specimens is housed in the National Museum of New Zealand in Wellington.

METHODS

Fifteen sites along the Summit Track and the Thumb Track were sampled at 50 metre altitude intervals. At each site a 10 by 10 metre quadrat was laid out and the dominant vegetation within the quadrat was noted. A leaf litter sample was collected for a later moisture analysis. An hour was spent collecting snails in the leaf litter and under fallen logs and branches, and a further 10 by 10 centimetre bag of litter was taken for later sorting, (see Fig. 1 for position of sites)

NOTE ON NOMENCLATURE

The nomenclature used in this paper, based upon the taxonomic studies of F.M. Climo, follows Solem et aL (1981). Because of the large number of undescribed species of New Zealand land snails (Solem et al put the number of described species at 315, with at least a further 205 species waiting to be described), particularly in the families Punctidae

29 Fig. 1. Map of site locations and dominant vegetation types on Summit Track and Thumb Track, Little Barrier Island. and Charopidae, many of the species are described by the term ' n. sp. ' followed by a number, which indicates an undescribed taxon of distinctive facies, whilst the term 'n.sp. aff.' conveys "a sense of shell morphotype". Similarly, quotation marks around the generic name indicate that "although presently placed in this genus, it may or may not have a definite phyletic affinity to the genotype" (Solem et al 1981).

RESULTS

Table 1. Species occurrence and frequency at each sampling site (the first of each paired number refers to the site while the number in brackets refers to the number of snails found at that site).

Cytora cytora (Gray 1850) -15(1) Cytora torquilla (Suter 1894) -1(7), 7(7) Champa coma (Gray 1843) -14(1) 'Charopa'pUsbryi(Suter 1894) - 2(2), 6(1), 8(1)

30 'Charopa' pseudanguicula (Iredale 1913) - 2(2), 10(2), 11(1) 'Charopa' chrysaugeia (Webster 1904) -10(3) Flammocharopa costulata (Hutton 1883) -15(1) Huonodon hectori (Suter 1890) - 3(12), 4(1), 5(4), 8(3) Cavellia cf. serpentinula (Suter 1891) - 8(10), 9(7), 10(1) Cavellioropa ci. microrhina (Suter 1909) - 9(2) 'Flammulina' feredayi (Suter 1891) - 7(1), 9(1) Therasia decidua (Pfeiffer 1867) -1(1), 7(2), 9(1), 11(2) Serpho kivi (Gray 1843) -1(1), 11(1) 'Allodiscus' urquharti (Suter 1894) -10(14), 11(1) Laoma leimonias (Gray 1850) -1(1) 'Laoma' pirongiaensis (Suter 1894) - 7(2), 14(2) 'Laoma' poecilosticta (Pfeiffer 1855) -11(1), 12(2) "Paralaoma'lateumbilicata(Suter 1890) -1(5), 3(8) 'Paralaoma' serratocostata (Webster 1906) - 7(1) 'Paralaoma' n.sp 1 -14(1) 'Paralaoma' n.sp.6 - 6(4) 'Paralaoma' n.sp. 29 - 3(8), 8(13), 9(1) 'Paralaoma' n.sp.30 - 7(2) 'Paralaoma' XLsp. 32 - 3(2), 9(1) 'Paralaoma' n.sp. 33 - 2(10), 4(2), 5(1), 8(2), 10(1) 'Paralaoma' n.sp. aff. 33-6(1) 'Paralaoma' n.sp.38 - 5(3) 'Phrixgnathus' cheesemani (Suter 1894) -1(1), 4(10), 5(8), 6(1), 8(1), 10(2), 11(4), 12(1), 13(6), 15(2) 'Phrixgnathus' conella (Pfeiffer 1862) - 2(1) 'Phrixgnathus'erigone(Gray 1850) -1(1), 4(2), 9(2), 11(5), 12(3). 13(1), 15(1) 'Phrixgnathus' glabriusculus (Pfeiffer 1853) - 5(1), 15(2) 'Phrixgnathus' moellendorffi (Suter 18%) - 3(5) 'Phrixgnathus' n.sp. 40-12(1), 14(1) 'Phrixgnathus' n.sp. 59 -10(1) Delos coresia (Gray 1850) -1(3), 6(1), 9(1), 15(1)

Table 2. Site descriptions.

site altitude litter dominant slope comments number (metres) moisture (%) ion 1 0 56 kanuka gentle little undergrowth sparse litter 2 20 63 kanuka gentle close to farmland many fallen branches 3 50 64 kanuka very dense undergrowth steep lots of litter 4 50 76 kanuka steep dense Doodia media sparse litter 5 100 64 kanuka medium sparse litter 6 100 67 kanuka medium 7 150 60 kanuka & gentle rocky slope with much moss beech 8 150 60 kanuka gentle litter in deep drifts site of prehistoric Maori excavations 9 200 68 kanuka steep much Astelia and Asplenium on ground

31 10 200 60 kanuka gentle deep litter, and dense vegetation & beech 11 250 55 kohekohe gentle many fallen logs 12 250 68 kauri gentle deep litter 13 300 75 kauri & very much Astelia, and litter in drifts some steep beech 14 350 74 beech & gentle much Astelia Kauri 15 400 77 beech & steep much Astelia and kidney ferns some kauri

DISCUSSION

Since collecting on this trip was confined to the wouth-western corner of the island, as compared to the more comprehensive survey of Milligan and Sumich (1953), the species list could conceivably be extended by sampling in other habitats on the island. In addition, since the collecting method concentrated on leaf litter and fallen logs, arboreal species are poorly represented, except for occasional dead shells in the litter (see Appendix I for revised list of species). Although slugs were not included in this study, it is worth mentioning that several individuals of an unidentified introduced species were collected at each of sites 1 to 5, all of which were in close proximity to the farmland and garden on the coastal flat. One introduced snail was found, a partially decomposed specimen of the genus Oxychilus. In addition, one Helix aspersa shell was found amidst drift debris on the beach, but its place of origin is unknown. An attempt was made to relate species distribution against the physical parameters of altitude, moisture and vegetation type. It was expected that altitude would have no significant effect, being chosen only as an easily measurable variable upon which to base site selection. Vegetation, as the source of litter, and litter moisture might be expected to be more important. The analysis was carried out using a general linear model for an unbalanced analysis of variance with SAS (statistical analysis system). Altitude gives an F value of 0.84 and is not significant in determining species distribution at any confidence level. Vegetation with an F value of 1.77, and litter moisture with an F value of 1.71 are similarly insignificant. However, a least squares regression analysis of Utter moisture against the number of snails collected shows a negative linear relationship which is significant at the 95% confidence level (the F value is 6.03) (see Fig. 2). Solem et al. (1981) propose that the "qualities of moisture retention and airspace (within the Utter) are more significant to the snails than the species of plant which provided the Utter". The results of this study tend to support this hypothesis. However, much more work is needed

32 POPULATION VS LITTER MOISTURE 35. 1 32.52

30.OJ

27.52

26.CC -

22.5Z N J U -I M

B 20.CC Ft 0 17.51 F

N 15.Oj A I L S 12.52

2.5:

riii»»rT|iinTii»T^mTiii ii|ii»nt?ti|irTFTtTTTTm 62 54 56 56 60 62 64 66 88 70 72 74 76 X MOISTURE CONTENT OF LITTER

Fig. 2. Graph showing fitted regression line of litter moisture against number of snails, with 95% confidence limits. Slope of line = -0.72; intercept on y-axis = 63.8; H = 0.317.

before this conclusion can be regarded as anything more than tentative. A point of note is the occurrence of "Phrixgnathus" cheese mam on Little Barrier Island - it is easily the most abundant of the species

33 collected in this study, yet it is now very rare on the mainland, with only two specimens existing in the reference collection of the National Museum (F.M. Climo pers. comm.)

ACKNOWLEDGEMENTS

The author would like to thank Mr H.G. Spencer and Dr F.M. Climo for assistance in the identification of species and preparation of the manuscript; Mr J. Wilkin for completing the computer analysis of data and others who have offered encouragement.

REFERENCES

Milligan, E.N. & Sumich, J.J. 1953: Mollusc species list of Little Barrier Island. Tane 6: 123-126. Solem, A.; Climo, F.M. & Roscoe, D.J. 1981: Sympatric species diversity of New Zealand land snails. New Zealand Journal of Zoology 8:453-485.

APPENDIX I. Land snails of Little Barrier Island - a revised species list (dates refer to year of collection).

LIAREIDAE Cytora cytora (Gray 1850) - 1953, 1981 Cytora pallida (Hutton 1883) - 1953 Cytora torquilla Suter 1894) - 1981 Liarea carinella (Pfeiffer 1861) - 1953 Liarea egea (Gray 1850) - 1981 Liarea turriculata (Pfeiffer 1855) - 1953 CHAROPIDAE Charopa coma (Gray 1843) - 1953, 1981 'Charopa' chrysaugeia (Webster 1904) - 1981 'Charopa' pilsbryi (Suter 1894)-1953,1981 'Charopa' pseudanguicula (Iredale 1913) - 1981 Flammocharopa cos tula ta (Hutton 1883) - 1981 Fectola infecta (Reeve 1852) - 1953 Huonodon hectori (Suter 1890) - 1953, 1981 Cavellia cf. serpentinula (Suter 1891) - 1981 Cavellia cf. sterkiana (Suter 1891) - 1953 Cavellia colensoi (Suter 1890) - 1953 Cavellia roseveari (Suter 1896) - 1953 Cavellioropa cf. microrhina (Suter 1909) -1981 Flammulina chiron (Gray 1850) - 1953 Flammulina perdita (Hutton 1883) - 1953 'Flammulina' feredayi (Suter 1891) - 1953, 1981 Therasia decidua (Pfeiffer 1857) - 1953, 1981 Serpho kivi (Gray 1843) - 1953, 1981 Therasiella celinde (Gray 1850) - 1953 Therasiella tamora (Hutton 1883) - 1953 Phenacohelix giveni (Cumber 1961) - 1953, 1981 Suteria ide (Gray 1850) - 1953 Mocella eta (Pfeiffer 1853) - 1981 Allodiscus planulatus (Hutton 1883) - 1953 'Allodiscus' urquharti (Suter 1894) - 1953, 1981 Otochoncha dimidiata (Pfeiffer 1853) - 1953

34 PUNCTIDAE Laoma leimonias (Gray 1850) - 1953, 1981 'Laoma' pirongiaensis (Suter 1894) - 1953, 1981 'Laoma' poecilosticta (Pfeiffer 1855) - 1953, 1981 'Paralaoma' lateumbilicata (Suter 1890) - 1953, 1981 'Paralaoma' serratocostata (Webster 1906) - 1981 'Paralaoma' n.sp. 1 - 1981 'Paralaoma' n.sp. 6 - 1981 'Paralaoma' n.sp. 29 - 1981 'Paralaoma' n.sp. 30 - 1981 'Paralaoma' n.sp. 32 - 1981 'Paralaoma' n.sp. 33 • 1981 'Paralaoma' n.sp.aff. 33 - 1981 'Paralaoma' n.sp.38 - 1981 'Phrixgnathus' allochroidus (Suter 1890) - 1953 'Phrixgnathus' ariel (Hutton 1883) - 1953 'Phrixgnathus' cheesemani (Suter 1894) - 1953, 1981 'Phrixgnathus' conella (Pfeiffer 1862) - 1953, 1981 'Phrixgnathus' erigone (Gray 1850) - 1953, 1981 'Phrixgnathus' glabriusculus (Pfeiffer 1853) - 1953, 1981 'Phrixgnathus' mariae (Gray 1842) - 1953 'Phrixgnathus' microreticulatus (Suter 1890) - 1953 'Phrixgnathus' moellendorffi (Suter 1896) - 1981 'Phrixgnathus' viridulus (Suter 1909) - 1981 'Phrixgnathus' n.sp. 40 - 1981 'Phrixgnathus' n.sp. 59 - 1953, 1981 Delos coresia (Gray 1850) - 1953, 1981 Delos jeffreysiana (Pfeiffer 1850) - 1953, 1981

Oxychilus sp. - 1981

Footnote PRESENT USAGE 1981 MILLIGAN & SUMICH, 1953 Therasia decidua Therasia decidua and T. zelandiae Phenacohelix giveni Phenacohelix ponsonbyi Mocella eta Fee tola (subfectola) caputspinulae 'Phrixgnathus' glabriusculus Phrixgnathus sublucidus 'Phrixgnathus' n.sp. 59 Phrixgnathus glabriusculus

35 36