A BRIEF HISTORY OF TUVALU'S NATURAL HISTORY K.A. Rodgers Department of Geology University of Auckland, Private Bag, Auckland New Zealand ABSTRACT The nine tropical, low islands of Tuvalu are surface expressions of thick deposits of calcareous biominerals overlying ancien! volcanic mounds. Present vegetation and terrestrial organisms lack variety and are limited in species. Marine fauna and flora are more varied. Following four major scientific expeditions in the 189Os, subsequent research in Tuvalu was largely limited to the fields of medical health and hygiene until the past fifteen years when new information on plants, soils, agricult\lre, fish and other marine organisms, and some fields of geology has been produced. INTRODUCTION The central Pacific nation of Tuvalu, the former Ellice Islands, consists of three small , low reef islands and six atolls strung out along an approximate north-north-west to south-south­ east bearing between 5° and 1O.5°S latitude and 176° and 179.5°E longitude. The roughly linear archipelago is part of the Austral-Gilbert-Marshall chain (Morgan, 1972) and is the surface expression of thick carbonate deposits draped over extinct volcanic mounds (Gaskell, Hill and Swallow, 1958). Volcanic rocks dredged from the flanks of Niulakita, the most southern of the group, are Cretaceous (Duncan, 1985). No age information is available for the northern islands. S. Pac. 1. Nal. Sci., 1991,11:1-14 2 , Nanumea 6' S • Niutao Nanumaga ~ N . Vaitupu UI ... {J Nukufetau 8' ? Funafuti o Nukulaelae 10' KILOMETRES o so 100 ISO Niulakita 20020406080 NAUTICAL MILES I 76'E 178' E 180'W Figure 1 Locality map. Tuvalu 3 From north to south the nine islands are (Fig. I ): 2 Nallumea - atoll with two main islets of 3.9 km ; 2 Niutao - reef island of 2.6 km ; 2 Nanumaga - reef island of 2.8 km ; 2 Nui - crescent shaped atoll with eight islets to the east, of 2.1 km ; 2 Vairupu - atoll of one broad, large (5.6 km ) island enclosing two small lagoons; Nukuferau - rhomb-shaped atoll of eight main islets of 2.8 km 2 around large lagoon; FUllafuri - pear-shaped atoll with 30 islets of 2.8 km 2 around large lagoon; Nukulaelae - atoll of 14 islets of 1.8 km 2 enclosing shallow lagoon; 2 Niulakita - small reef island of 0.4 km . No part of any island exceeds 8 m elevation above sea level with few pans exceeding an elevation of 4 m. The climate is uniformly hot with relatively high humidity. The prevailing easterly trade winds help cool the islands and the temperature varies between a daily ~aximum of 31 °C and a minimum of 25°C. Annual rainfall ranges from 2500 mm in the northern islands to 3500 mm in the south, mostly occuning as heavy showers. Wellest months are from December to March, which roughly corresponds to a change in winds from the north and west. Winds are generally light to moderate. Tropical cyclones are rare: for example, they struck in 1891 , ) 972 and 1990. Severe droughts have periodically affected the islands. Soils are usually very weakly developed on porous coralgal sand and rubble - calcaric regosols. Vegetation is limited to some three. dozen species among which coconut palms, pandanus, casuarina and salt tolerant ferns, creepers and grasses predominate. Pisonia woodland probably occupied the bulk of the islands in the distant past with only scattered pockets remaining today. Rare patches of mangrove swamp occur. In moist hollows, including man-made pulaka (taro) pits, soils are augmented with humus to support a subsistence gardening. The main plants cultivated are coconuts, breadfruit, pawpaw, bananas, and taro. Tuvaluan terrestrial wildlife lacks variety. Land vertebrates are not common and limited in s[lecies. They include birds, rats and lizards. The sea is rich in fish , squid. crabs, 4 foraminifera, corals and algae, the last three being the main builders of broad reef platforms which encircle all of Tuvalu's islands. The similar chain of islands of Kiribati lies north and east. Otherwise the nearest land is Rotuma, 400 Ian to the south-west, with the main islands of Fiji a further 200 Ian south. The Phoenix and Tokelau groups occur about 700 Ian east. The Santa Cruz Islands make the first landfall 1500 Ian west. As a consequence of Tuvalu's geographic isolation, the 26 square Ian of the archipelago provides the sole land area due south of the Equator and west of the 180" meridian, in 2,000,000 lan2 of the central Pacific, which Doty (1954, pp.367-8) suggested may well "prove to be an important biotic province." Geology and biology are intimately linked where atolls rise. All atoll land is made of biominerals. These not only constitute the chief products in the islands ' geochemical cycle but, along with atmosphere, sea and rainwater, are also the principal reactants. Tuvalu's mineral deposits are restricted to the dominant limestones with scattered pockets of phosphatized limestone occuring on all the islands, ranging in size from it few grams to >500,000 tonnes on Niulakita. Dolomitic limestones and dolostones have been found at depth beneath the reef at Funafuti. HISTORY OF RESEARCH Funafuti, the largest atoll of the group and now the centre of Government, was the site for three expeditions mounted by the Royal Society in 1896, 1897 and 1898. The primary purpose of these expeditions was to bore to great depth into the underlying reef and retrieve rock samples for study. The first expedition was headed by Professor W.l. Sollas of Oxford who was accompanied by Stanley Gardiner of Cambridge and Charles Hedley of the Australian Museum. Two borings were attempted using a drilling rig supplied by the New South Wales Department of Mines, but reached only 105 ft and 74 ft. Considerable data on the reef along with extensive collections of natural history specimens were obtained, as well as useful geophysical measurements made by the officers of the gunboat HMS Penguin (Cantrell and Rodgers, 1988; Rodgers and Cantrell, 1989a). Professor Edgeworth David of Sydney led the 1897 expedition. He achieved the original objective of the ~oyal Society by .boring to a depth greater than 600 ft, although the bit remained in limestone, instead of penetrating the assumed volcanic undermass. The drilling crew under the direction of George Sweet of Melbourne, reached a depth of 698 ft before its activities were abandoned for the year (Cantrell and Rodgers, 1989). David initiated a programme for mapping the whole of Funafuti in detail, and described the geology of all islets. 5 Alfred Finckh of Sydney led the third expedition (Rodgers and Cantrell, 1989b). He drove the drill-bit to 1114.5 ft before running out of cutting diamonds in October 1898. Again the bit remained in calcareous reef ~ock. Finckh continued mapping of the atoll and systematically dredged the outer face of the reef. He undertook a further study of the development and growth of reef rock. Finckh was accompanied by Gerald Halligan, Hyarographer to the New South Wales Government, who arrived on board HMS Dolphin. Halligan's iask was to sink a bore into the centre of the lagoon from the bow of the Dolphin to obtain further samples for study to complement those being obtained onshore. With Finckh's assistance, he also dredged a series of shallow sediment samples across the full width of the lagoon. Shortly after Finckh's departure at the end of 1898, Professor Alexander Agassiz of Harvard arrived on board the USS Albatross. He reported that: "On all islands with rock exposures, we came across the hammer marks of Messrs Sollas and David" (1903:219). When the wealth of scientific information collected by these four expeditions was published it served for a time to make Funafuti a centre of attention for the world's scientific community. Geologists described the lagoonal sediments, reefs, submarine topography, stratigraphy, deep structure, and petrologic composition. In addition, reports appeared of the collections of the flora and fauna. Funafuti became the best documented atoll in the Pacific and Indian Oceans by the turn of the century (Rodgers, 1985; Rodgers and Cantrell, 1988). Following this brief, intense activity, most of the world's scientists lost interest in these remote and tiny islands. Their isolation and diminutive size contributed to their being bypassed by many Pacific researchers. Prior to the Roy~ Society expeditions most information of scientific value, as well as the few collections which existed in he,baria and museums had come largely from missionary sources (e.g. Mueller, 1876; Butler, 1878; Sharpe, 1878). These collections were not systematic or comprehensive, but neither were the majority of those made during the Royal Society visits to Funafuti. Few had been assembled by any specialist in any particular field. Further, some identifications were to prove flawed (e.g. see criticisms of North, 1898; Pocock, 1898; Bogert, 1937; Belkin, 1962; Pont, 1968). Yet, apart from areas directly related to health and hygiene, little new field evidence or specimens was to become available until the 1970s to build on the accomplishments of Sollas, Gardiner, Hedley, David, Sweet, Finckh, Halligan and Agassiz. One difficulty which was, and still is apposite to Tuvalu was highlighted by Katherine Luomala: "Often generalizations for the entire group or for the entire Gilbert and Ellice 6 Islands Colony probably apply only to specific islands" (1975, p.277). Until very recently little has been documented on the geology and biology of the eight outer islands, although Agassiz had cursorily surveyed some of their reefs and collected a few specimens. Dr Sixten Bock from Sweden stopped by in mid-1917 while much of the rest of the world was at war.