ATOLL RESEARCH BULLETlN NO. 235 Issued by E SMTPISONIAIV INSTITUTION Washington, D.C., U.S.A. November 1979 CONTENTS Abstract Introduction Environment and Natural History Situation and Climate People Soils and Vegetation Invertebrate Animals Vertebrate Animals Material and Methods Systematics of the Land Crabs Coenobitidae Coenobi ta Coenobi ta brevimana Coenobi ta per1 a ta Coenobi ta rugosa Birgus Birgus latro Grapsidae Geogxapsus Geograpsus crinipes Geograpsus grayi Metopograpsus Metopograpsus thukuhar Sesarma Sesarma (Labuaniurn) ?gardineri ii Gecarcinidae page 23 Cardisoma 2 4 Cardisoma carnif ex 2 5 Cardisoma rotundum 2 7 Tokelau Names for Land Crabs 30 Notes on the Ecology of the Land Crabs 37 Summary 4 3 Acknowledgements 44 Literature Cited 4 5 iii LIST OF FIGURES (following page 53) 1. Map of Atafu Atoll, based on N.Z. Lands and Survey Department Aerial Plan No. 1036/7~(1974) . 2. Map of Nukunonu Atoll, based on N.Z. Lands and Survey Department Aerial Plan No. 1036/7~sheets 1 and 2 (1974). 3. Map of Fakaofo Atoll, based on N.Z. Lands and Survey Department Aerial Plan No. 1036/7C (1974). 4. Sesarma (Labuanium) ?gardineri. Dorsal view of male, carapace length 28 rnm from Nautua, Atafu. (Photo T.R. Ulyatt, National Museum of N. Z.) 5. Cardisoma carnifex. Dorsal view of female, carapace length 64 mm from Atafu. (Photo T.R. Ulyatt) 6. Cardisoma rotundurn. Dorsal view of male, carapace length 41.5 mm from Village Motu, Nukunonu. (Photo T.R. Ulyatt) LIST OF TABLES 0 I. Surface temperature in the Tokelau Islands ( C) Page 5 11. Mean rainfall in the Tokelau Islands (mm) 6 111, Comparative list of crab names from the Tokelau Islands, Samoa, Niue and the Cook islands, 3 5 IV. Numbers of land crabs in live quadrats on Atafu Atoll, January-February 1973, 39 by J.C. yaldwynl and Kazimierz wodzicki2 ABSTRACT The Tokelau Islands consist of three atolls (Atafu, Nukunonu and Fakaofo) approximately 500 km north of Western Samoa. Their numerous islets are formed mainly of coral sand and rubble with no standing freshwater. Sixty-one plant species have been recorded, 13 of these being introduced and 10 being adventives, There are three vegetation zones, the beach, the beach-crest, and the interior coconut/fern zone with the physiognomy of a humid tropical forest. Marine invertebrates have not been studied. One hundred and fifty insect species in 83 families have been recorded with most being widely distributed South Pacific species including several introduced agricultural pests, e.g, Rhinoceros Beetle. Some marine fishes have been listed and 7 species of lizards are known from the group. Twenty-six bird species (15 sea birds, 8 shore birds and 3 land birds) are known but none are endemic races. Domestic pigs, cats, man and the Polynesian Rat (Rattus exulans) are the only mammals. R. exulans is an economic pest as it causes considerable damage to the coconut crop and assists in the spread of filariasis, Ten species of "land crabs" are identified from the Tokelaus, 4 being terrestrial hermit crabs of the anomuran family Coenobitidae (3 Coenobita spp, and Birgu:~; latro) and 6 being terrestrial crabs of the brachyuran families Grapsidae (2 Geograpsus spp., a Metopograpsus and a Sesarma) and Gecarcinidae (2 Cardisoma spp.) . Eight of these species have been recorded before from the Tokelaus under one name or another but two, Geograpsus grayi and Metopograpsus thukuhar, are new records for this group of atolls. The total of LO land crab species National Museum of New Zealand, Wellington, New Zealand. Zoology Department, Victoria University of Wellington, New Zealand. (Manuscript received December, 1977. --Eds .) from the Tokelaus can be compared numerically with 15 species on one atoll (Arno) in the Marshall Islands, 9 on one atoll (Kapingamarangi) in the Carolines and 7 from one atoll (Raroia) in the Tuamotus. All the land crab species from the Tokelaus (except for Sesarma ?qardineri known elsewhere only from New Guinea and southern Micronesia) are wide- ranging Indopacific forms known from at least the western Indian Ocean to the eastern central Pacific. Fourteen different crab names in the Tokelau language are recorded and identified. Vernacular names for common land crabs such as uga (Coenobita brevimana) , uqauga (Birgus latro), paikea (Cardisoma rotundum) and kalamihi (Geoqrapsus crinipes) are used with minor modifications for similar species in Samoa, Niue and the Cook Islands. A traditional story about the kaviki (the shore crab, Ocypode ceratophthalma) recorded by Dr. Judith Huntsman of the University of Auckland, is given in translation. All land crab species on the Tokelaus are nocturnal scavengers. Population counts of Coenobita brevimana and C. perlata together, Birgus latro, Cardisoma rotuiidum, C, carnifex, and Geograpsus crinipes give a combined density of about 560 crabs per 5000 sq. m. This figure can be compared to approximately the same land crab density figure on Kapingamarangi Atoll in the Carolines (Niering, 1956) but is in dramatic contrast to counts of approximately 30,000 Cardisom planatus per 5000 sq. m on Clipperton Atoll in the eastern tropical Pacific (Ehrhardt, 1968). The numerous land crabs on the Tokelaus have an indirect effect on rat control programs and a direct effect on R. exulans themselves. Crabs interfere with rat traps and poison baits, eating both warfarin and zinc phosphide. The effect of the anticoagulant warfarin on crabs is unknown, but quadrat counts show that crabs are severely affected by zinc phosphide. The slight risk to humans of secondary poisoning from eating affected crabs can be virtually eliminated by banning crab collecting in poisoned areas for periods after poison baiting, and by putting poison baits in aluminium tubes of a diameter small enough to exclude large and sought-after species such as Birqus Zatro and the two Cardisoma spp. Large land crabs presumably prey on young rats, thereby forcing rats to nest above ground level, and compete with rats for at Least one of their important foods, the coconut meat available in man-opened and abandoned nuts. INTRODUCTION There is no comprehensive information on the systematic status and biology of "land crabs" (both terrestrial hermit crabs and terrestrial true crabs) on islands in the central and south Pacific, Holthuis (1953) in his enumeration of crustacean species from coral atolls in the Marianas, Marshalls, Gilberts and Tuamotu Islands lists, but does not comment on, seventeen species of land crab in the families Coenobitidae (land hermit crabs), Grapsidae and Gecarcinidae (true crabs). Niering (1956: 16-18) recorded nine land crab species of these families from Kapingamarangi Atoll in the Carolines and gives a general, but vivid, description of their habits. An extensive summary of the published information on the general ecology of land crabs on Pacific atolls is given in the excellent review of atoll environment by H.J. Wiens (1962: 432-439). One of us (K.W.) visited the atolls of the Tokelau group on four separate occasions (November 1966 - February 1967 and April - June 1968, Nukunonu Atoll; July - September 1971, Fakaofo Atoll; December 1972 - February 1973, Atafu Atoll) working on the problem of rat damage to coconuts (Wodzicki, 1968a, 1968b, 1969a, 1970, 1972a, 1972b, 1973a, 1973b, 1973c; Mosby and Wodzicki, 1972; Mosby, Wodzicki and Shorland, 1974; Mosby, Wodzicki and Thompson, 1973). During his early visits he made incidental collections of land crabs and was surprised at both the systematic variety and the abundance of these animals. On the suggestion of J.C.Y., he made a special collection of land crabs during his last trip concentrating on obtaining a coverage of the different species present, particularly those with "specific" Tokelauan names. The 1972/73 visit to Atafu Atoll produced a list of seven different land crab species and these have already been recorded in a preliminary report on this visit (Wodzicki, 1973~). K.W. had previously recorded that land crabs seriously interfere with snap and live-trapping of rats on the Tokelaus (Wodzicki, 1968a: 56) and then added details of interference with ground-placed poison baits (1973~:21,29) . As the coconut crab (Birgus latro) and to a lesser extent other land crabs are a part of the Tokelauan diet, he was aware that the use of acute poisons in rat control, such as zinc phosphide, might create the danger of secondary poisoning of humans. During a concurrent survey (Wodzicki, 1969b) of rat ecology and damage on Niue Island, an isolated raised atoll south-east of Samoa, K.W, made similar collections of land crabs and these will be the subject of a future study. The purpose of the present paper is to provide a detailed account of the systematic status and local names of the ten land crabs on the Tokelau Islands, to comment on their ecology and significance in these atolls, and to discuss the local problem of rat-crab relationships. ENVIRONMENT AND NATURAL HISTORY Situation and Climate The Tokelau (or Union) Islands consist of three atolls, named from west to east Atafu, Nukunonu (sometimes misspelt "Nukunono", see Wodzicki and Laird, 1970: 247) and Fakaofo. Their eighteenth and nineteenth century European names, not now used, are Duke of York, Duke of Clarence and Bowditch Islands respectively. The Tokelaus are bounded by latitudes ~OSand 100s and by longitudes 171°w and 173O~. The atolls are approximately 500 km to the north of Western Samoa; Nukunonu is about 90 km south and east of Atafu and Fakaofo is about 65 km east of Nukunonu. They are typical atolls, each being surrounded by a coral reef with an inner lagoon. The numerous islets (or motus) of each atoll vary in number and size but do not rise more than 3 to 5 metres above sea level. The total land area of the Tokelaus is about 11.5 sg.km and the areas of the three atolls are approximately as follows (revised 1975 figures, N.Z.