Atolls of the Tropical Pacific Ocean: Wetlands Under Threat
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Atolls of the Tropical Pacific Ocean: Wetlands Under Threat R. R. Thaman Contents Introduction ....................................................................................... 2 Pacific Atolls Described .......................................................................... 3 Distribution ....................................................................................... 5 Atoll Biodiversity ................................................................................. 6 Ecosystem and Habitat Diversity ................................................................. 7 Species and Taxonomic Diversity ................................................................ 10 Genetic Diversity ................................................................................. 13 Ecosystem Goods and Services .................................................................. 13 Threats and Future Challenges ................................................................... 13 Conservation of Atoll Ecosystems ............................................................... 19 Conclusion ........................................................................................ 22 References ........................................................................................ 23 Abstract Atolls are small, geographically isolated, resource-poor islands scattered over vast expanses of ocean. There is little potential for modern economic or com- mercial development, and most Pacific Island atoll countries and communities depend almost entirely on their limited biodiversity inheritances for ecological, economic, and cultural survival in a rapidly globalizing world. Atolls rarely have elevations over 2 or 3 m above sea level and commonly have extensive areas of intertidal flats, mangroves, shallow lagoons, coral reefs, and limited areas of brackish water marshes or landlocked fossil lagoons and are subject to periodic tidal inundation during extreme weather and tidal events, such as “king tides”. Under the Ramsar Convention definition, atolls and their nearshore waters are essentially “wetlands.” Although arguably among the Earth’s “biodiversity R.R. Thaman (*) The University of the South Pacific, Suva, Fiji e-mail: [email protected]; [email protected] # Springer Science+Business Media Dordrecht 2016 1 C.M. Finlayson et al. (eds.), The Wetland Book, DOI 10.1007/978-94-007-6173-5_270-1 2 R.R. Thaman coolspots” with the poorest and highly threatened terrestrial biodiversity inheri- tances on Earth, they are among the last remaining sanctuaries for extensive, but highly threatened populations of breeding seabirds and coral reef-associated biodiversity. Fortunately, under Ramsar, UNESCO World Heritage, and other relevant conventions and initiatives, the conservation, restoration and sustainable use of atoll biodiversity and associated ethnobiodiversity (the uses, knowledge, beliefs, management systems, taxonomies and language that traditional and the scientific communities have for biodiversity) is now clearly on the conservation agenda. Keywords Atolls • Biodiversity cool spots • Ethnobiodiversity • Coastal plants • Coral reef diversity • Food and livelihood security • Global change • Lagoons • Mangroves • Marine biodiversity • Pacific Islands • Sea birds Introduction Atolls are small, geographically isolated, resource-poor islands scattered over vast expanses of ocean. There is little potential for modern economic or commercial development, and most Pacific Island atoll countries and communities depend almost entirely on their limited biodiversity inheritances for ecological, economic, and cultural survival. Atolls rarely have elevations over 2 or 3 m above sea level and commonly have extensive areas of intertidal flats, mangroves, shallow lagoons, coral reefs, and limited areas of brackish water marshes or landlocked fossil lagoons and are subject to periodic tidal inundation during extreme weather and tidal events, such as “king tides” (Thaman 2008). Under the Ramsar Convention definition, atolls and their nearshore waters are essentially “wetlands.” Atolls are the opposite of “biodiversity hot spots”–areas such as Amazonia, Southeast Asia, Australia, and many Pacific Island areas such as New Guinea, New Caledonia, Solomon Islands, Hawaii, and the Galapagos – which have very high species and ecosystem diversity and high levels of endemism that are under threat of extinction and degradation (Whittaker 1998). Atolls are among the Earth’s “biodi- versity cool spots” because they have few, if any, endemic plants and animals and among the most impoverished and highly threatened terrestrial and freshwater biodiversity inheritances on Earth, with a high proportion of all economically, culturally, and ecologically important terrestrial plants and animals in danger of extirpation (local extinction) (Thaman 1992a, 2008). Although not as impoverished, atoll marine biodiversity is also under threat and in danger of extirpation, especially on inhabited and urbanized atolls. Despite the poverty, fragility, threatened status, and the obligate dependence of atoll peoples on biodiversity, atoll biodiversity has received only limited attention from the international conservation community, which has focused mainly on the Earth’s “biodiversity hot spots” (Thaman 2008). Fortunately, under Ramsar and a number of other conservation initiatives, Kiribati, the Marshall Islands, and a Atolls of the Tropical Pacific Ocean: Wetlands Under Threat 3 number of other Pacific Island atoll countries have designated atolls or atoll islets as “conservation areas” or initiated other initiatives to conserve atoll biodiversity. This chapter discusses the nature of atolls, atoll biodiversity, its value to atoll countries and communities, the threats to and conservation status of atoll biodiversity, and some conservation initiatives, including Ramsar initiatives, that have catalyzed the conservation of atoll biodiversity. Although there are atolls elsewhere, such as the Maldives in the Indian Ocean, the focus is on all atoll nations and atolls and low-lying limestone reef islands of the cultural regions of Melanesia, Polynesia, and Micronesia in the tropical Pacific Ocean (Fig. 1). Pacific Atolls Described The word atoll comes from the Malayalam word atolu or “reef” or atollon, the native name for the Maldives Archipelago (Newhouse 1980). Adapting the definitions of Bryan (1953) and Wiens (1962), the term “atoll” refers here to all low-lying oceanic limestone reef islands, with or without lagoons, that have formed on barrier reefs or in the shallow lagoons along the coastlines, or encircle long-submerged ancient volcanoes, which are not associated with nearby high islands or continents (Fig. 2). The term “islet” refers to the individual smaller islands or “motu” (a Polynesian name for reef islets) that are found on the reefs or in the lagoons of the main atoll islands. In other words, “atolls” include both “true atolls,” the islets of which encircle, border, or are found within a lagoon, and individual, separate low-lying limestone reef islands that have no lagoon or may have “secondary” or remnant “fossil” lagoons on the actual limestone island or islets (Thaman 2008). Most atolls have maximum elevations below 3–4 m above sea level, although some have limited areas of coral rubble ramparts deposited over time by high storm waves, limestone pinnacles (e.g., the raised limestone pinnacles on Tikehau Atoll in French Polynesia (Fig. 3), or windblown sand “dunes” that can reach elevations of over 10 m (e.g., Joe’s Hill which attains 13 m on Kiritimati Atoll in Kiribati). Excluded from this definition of atolls are raised limestone islands or “raised atolls” that have average elevations much higher than 5 m, such as the main islands of the Tongatapu, Ha’apai, and Vava’u groups of Tonga and Ouvea, Lifou, and Mare in the Loyalty Islands of New Caledonia; raised phosphatic limestone islands, such as Nauru and Banaba (Ocean Island) and Makatea in the Tuamotus; and barrier reefs and associated islets surrounding high islands or continents, such as the “almost atolls” of the main Chuuk group and Bora Bora in French Polynesia and islets and reef structures with associated islands such as those on the Great Barrier Reef off northeastern Australia. Also excluded from this definition are “sunken atolls” with- out dry land, such as Middleton and Elizabeth Reefs in the Coral Sea off Australia (Thaman 2008). The above definition of atoll is relatively clear for most of the well-studied “atolls” of Polynesia and Micronesia, although the status of many of the small islands included as atolls in the islands of Melanesia is uncertain due to the lack of detailed published information. For example, Bryan (1953) listed the island of 4 R.R. Thaman Fig. 1 Distribution of the main atoll countries and territories in the Pacific Ocean in the cultural regions of Micronesia, Melanesia, and Polynesia (J. Lowry # Rights remain with the author) Atolls of the Tropical Pacific Ocean: Wetlands Under Threat 5 Fig. 2 Wailagi Lala Atoll, Fiji, partially obscured by cloud (Photo credit: R.R. Thaman # Rights remain with the author) Ouvea in the Loyalty Islands to the east of New Caledonia as the “world’s largest atoll,” although by his own definition, it is clearly not, but rather a large raised limestone island rising to a maximum elevation of 46 m, much more similar to some of the islands of Tonga, mentioned above (Thaman 2008). Distribution Globally, the Earth’s oceans contain more than 400 “atolls” composed