Rose Atoll: an annotated bibliography

Abstract

Over 290 citations of published monographs, articles from learned journals, periodical features, official reports, letters, notes, some limited circulation andlor unpublished documents, and unofficial reports, concerned with the geology, geography, pedology, biology, meteorology, oceanography and history of Rose Atoll, American Samoa, are indexed and annotated. RODGERS, K.A., I.A.W. MCALLAN, C. CANTRELL & B.J. PONWITH. 1992. Rose Atoll: an annotated bibliography. Technical Reports of the Australian Museum 9: 1-37. Rose Atoll lies at the extreme eastern end of the Samoan island volcanic chain (14'32's 168"08'W), 240 km east-south-east of Pago Pago Harbor (Fig.1). It is of a roughly square shape. The fringing reef and lagoon together cover just 640 ha making it one of the smallest atolls in the world. The fetch of the lagoon is about 2 km and the maximum depth about 20 m. The coralline algal reef has a uniform, 500 m width and is largely submerged at low tide. A single channel in the north-east, 1.8-15 m deep, links the lagoon to the sea. The atoll is one of the least disturbed areas of the world. Its benthic community is unique in Samoa, being dominated by encrusting coralline algae, and having a relative abundance of soft corals with a comparable impoverishment in hard species (Itano, 1987, cited in United Nations Environment Programme, 1988). The atoll has been established as a National Wildlife Refuge since 5 July 1973, and annual resource surveys are carried out by US Fish and Wildlife Service and American Samoan Government personnel. These include both the lagoon and outer reef as well as the islets, thus affording an invaluable scientific baseline for biological and geological studies of low Pacific islands. Excellent summary reviews of the history and natural history of the atoll are given by Setchell (1924) and Sachet (1954). A highly detailed, up-to-date account of the terrestrial biology is contained in Amerson et al. (1982a,b). 2 Technical Reports of the Australian Museum (1993) Geological and Biological Notes The Samoan Islands are part of a chain of searnounts, shallow banks and drowned atolls which extend 1700 km to the north-west. All are volcanic in origin and lie in a line with the correct orientation to have been generated by the present motion of the Pacific plate over a fixed hot spot (Natland, 1980; Menard, 1986). Both the size of the islands, and the proportion of them covered by Quaternary lava flows, increases to the west, in contrast to the Hawaiian, Society, and Marquesas chains. In these lineaments, submerged volcanic mounds, both drowned and capped by atoll reefs, occur at the western end, but in the Samoan chain Rose Atoll lies to the east. The age of Rose's volcanic substrate is not known, but it could be very young (Natland, 1980 but cf. Menard, 1986). Unlike the seemingly more mature, drowned atolls and flat banks to the west, Rose lacks wide offshore banks. In his studies of the petrology of the Samoan chain, Natland seems to have been unaware that basalt rocks had been reported and recovered from Rose (e.g., Natland, 1980; Natland & Turner, 1985). The nature of these particular rocks, and even their very existence, has been a subject of some confusion in the literature. They were first reported by members of the United States Exploring Expedition (e.g., Couthouy, 1844; Wilkes, 1844; Dana, 1851; Pickering, 1876). Mayor (1921b, 1924b) specifically looked for but failed to find any trace of them and he and Setchell (1924) dismissed the earlier reports as incorrect identifications of weathered limestone. However, Schultz (1940, 1943), located and collected from a dozen basalt boulders lying loose on the reef flat. Sachet (1954) reported that Gilbert Corwin of the US National Museum had identified the samples as olivine basalt. There are only two islets upon the reef (Fig.l,2): Rose Island in the east and Sand Island to the north. Total land area is 7.77 ha. Aggradation and degradation are active around the islets' margins and published descriptions of the atoll indicate that variation has occurred in area, shape and even position of the islets within historic times (e.g., Mayor, 1921b; Setchell, 1924; Bryan, 1938; Schultz, 1943; Amerson et al., 1982a; Ludwig, 1982a; cf. Sachet, 1954: 1-2; and see Figs 1,3acpa-d). Rose displays the dynamic character so typical of low islands in general, and atolls in particular. Perhaps, the small size of the atoll has helped heighten different observers's awareness of its active physical environment. The following descriptions are taken in large part from United Nations Environment Programme (1988) report of Susan Wells. Rose Island is located on the lagoon half of the reef in the windward corner of the atoll square (Fig.1). It is a roughly oval islet about 180 X 200 m, covering 5.18 ha, having a 1.0 km shoreline, and a maximum altitude of 3.0 m (Fig.2). It consists of raised reef rock and a coquina of worn fragments of lithothamnium, Favites, Porites, Symphallia, Pocillopora, Acropora, Tridacna, Fig.1. Sketch map of Rose Atoll, after Amerson et al. (1982a). Insert indicates location of Rose within the Samoan island chain. Rodgers et al.: Rose Atoll, bibliography 3 gastropod shells and echinoderms. A phosphatic soil, rich in humus has developed on the coquina beneath a large grove of Pisonia grandis. Sand Island is a bank of coralgal sand with an 0.5 km shoreline and reaching about 5.2 m above sea level. It covers 2.59 ha and presently lies on the lagoon side of the reef, due east of the lagoon entrance channel, with a broad reef flat extending seawards. It is intermittently vegetated and following Humcane Ofa in February 1990, it was swept clear save for one Messerschmidia tree. It now hosts seedling growth of Boerhavia and Messerschmidia. The lagoon floor has an undulating sandy bottom much of which is covered with algae and small scattered colonies of Acropora. Flat-topped, steep-sided pinnacles jut up from the floor and are encrusted by coralline algae, with both hard and soft corals on the vertical and undercut sides. Descriptions of the reef and the reef flat are given by Mayor (1921b) and Wass (n.d. a,b) which are summarised in United Nations Environment Programme (1988). The upper surface of the reef is a hard, smoothfloored flat, awash at low tide, and covered with vigorous growths of Porolithon that form connected pink patches and ridges up to 15 cm high and 15 cm to a metre or more wide. The inner lagoon edge is covered by coral blocks, the larger of which have flattened tops, also encrusted by coralline algae, and with both algae and soft corals coating their sides. Most of these blocks lie loose on the flat but some are attached by slender pedicels. Mayor (1921b) noted one loose boulder which he estimated weighed 46 tons. He argued (1921b, 1921c, 1924b) that the appearance of these boulders lent support to the rim of the atoll having once been 6 to 8 feet (1.8-2.4 m) higher than at present (cf. Stoddart, 1969). The remainder of the reef flat is rubble-strewn and also heavily encrusted by coralline algae and scattered colonies of Acropora. The basalt boulders, noted earlier, are part of the rubble of the flat. Their apparent comings and goings give further indication of the dynamic nature of the atoll environment. The reef front extends from a depth of 4 m in a series of irregular steep steps to about 50 m depth. The upper portion is dissected by ridges and surge channels. The irregular, high magnesium calcite substrate is encrusted thickly with coralline algae. Corals, including Acropora and Pocillopora, are abundant and diverse but table and staghorn varieties are lacking. No reports of the outer reef have been published at the time of writing. Several authors (e.g., Setchell, 1924; Sachet, 1954) have drawn attention to the number of native vascular plant species found on Rose being restricted to three: Pisonia grandis, Boerhavia tetrandra, and Portulaca lutea which form a small evergreen orthophyll softwood forest. At the time of their intensive survey of the atoll, Amerson et al. (1982a,b) found the number of species had increased to include Messerschmidia argentea, Ipomoea macrantha, and Suriana rnaritima, the latter having anived only very recently. Several attempts have been made to introduce coconut palms Cocos nucifera. The number surviving varies (20 in 1938, 12 in 1953), as do reports of their health (cf. Sachet, 1954:5,16). Fig.2. Aerial photograph of Rose Island about 1988. Department of Marine and Wildlife Resources, Pago Pago. 4 Technical Reports of the Australian Museum (1993) To Pacific ornithologists Rose means seabirds. All observers have commented on the very large seabird population which dominates the life of the atoll. About 97% of the total seabird population of American Samoa is resident on Rose, consisting of about 312,000 birds of 20 species. There are large nesting colonies of both the Greater and Lesser Frigatebirds (Fregata minor and F . ariel), of the Red-footed, Brown and Masked Boobies (Sula sula, S. leucogaster and S . dactylatra), of Redtailed Tropicbirds (Phaethon rubricauda), of White and Sooty Terns (Gygis alba and Sterna fuscata), of Brown and Black Noddies (Anous stolidus, A. tenuirostiris), and of Reef Herons (Egretta sacra). In addition about a dozen migrants and visitors have been recorded from the atoll including the White-tailed Tropicbird (P. lepturus), Pacific Golden Plover (Pluvialisfulva), Ruddy Turnstone (Arenaria interpres), Bristle-thighed Curlew (Nurnenius tahitiensis), Bar-tailed Godwit (Limosa lapponica), Wandering Tattler (Heteroscelus incanus), Sanderling (Calidris alba), Long-tailed Cuckoo (Urodynamis taitensis). A small white egret has been reported by Scott et al. (1983). Hawksbills, Eretmochelys imbricata, and Green Turtles, Chelonia mydas, nest on the atoll. Other herpetofauna records include Gehyra oceanica, the Polynesian Gecko and Lepidodactylus lugubris, the Mourning Gec