Kiritimati (Christmas Island): The Physical Environment

Figure 1. Hyper-Saline Lake, David Siu 2011

The Republic of Kiribati (pronounced Kiribas) is a low-lying coral atoll island nation made up of thirty-three atolls, and is comprised of the Phoenix, Line and Gilbert archipelagos located in the central tropical Pacific Ocean. The Exclusive Economic Zone (EEZ) of the Republic of Kiribati spans more than 3.5 million km2. Kiritimati (pronounced Christmas) is located in the northern Line Islands and comprises over 70% of the total landmass of Kiribati. The island is located 2,100 kilometers southeast of the Hawaiian Islands (1º 52’N, 157º20’W), and it is the world’s largest coral atoll by land area, with a total contiguous landmass of 388 km2 (Thomas, 2003).

Figure 2. Geographical Location of the Republic of Kiribati and Island Map for Kiritimati, David Siu 2011

The United Kingdom claimed these islands in 1892 and maintained control until 1979. In the late 1950s and early 1960s Kiritimati was used for the testing of nuclear weapons by the United States and United Kingdom. The island had only been previously inhabited by people working in copra production. The sparsely inhabited island suddenly had a population of foreign military forces and support workers from surrounding islands. After the end of nuclear testing on Kiritimati, many of the workers remained settled on the island and the population has since further grown due to migration and active resettlement from the overcrowded capital of Kiribati, Tarawa.

Today, Kiritimati faces issues of overpopulation and insufficient resources to support its inhabitants. The entire island relies heavily on imports, even for simple necessities like food.The soil of the island lacks essential nutrients for agriculture and the waters around the island have been overfished in recent years. The limited flora and fauna of Kiritimati Island reflect its nutrient deficient soils, scarcity of freshwater, and its remote location in the middle of the Pacific Ocean. Furthermore, the people of Kiritimati face an even greater danger from rising sea levels threatening to consume their low lying island.

The Line Islands were formed over millions of years as the Pacific Plate moved over a hot spot, making volcanic islands in the middle of the Pacific Ocean. During atoll formation, new islands are created by volcanic activity, around which grow fringing coral reefs. As the coral reefs progressively grow upward to keep up with the sea level, the cooling volcano sinks and erodes away until only a lagoon is left within the reef. Kiritimati is also being uplifted due to tectonic rising. This means that the old reef, which now forms the landmass of the island, is actually being pushed up and out of the water. The shape of an atoll is further determined by current- and wind-induced erosion of the reef. Kiritimati is one of the world’s oldest atolls, believed to have emerged during the Holocene Period (Saenger et al., 2006). The modern lagoon on Kiritimati is roughly 320 square kilometers, with 48 kilometers of shoreline and three minor islands within the main lagoon (Trichet, 2001). The lagoon is relatively shallow with a fine sandy substrate. It is an important marine resource for islanders as it provides fresh food and it attracts top-paying sports fishermen with its world renowned lagoon bonefish (Thomas, 2003).

Kiritimati’s soil quality is poor due to the lack of organic matter on the island (UNEP). The soil is relatively undeveloped and has very low concentrations of potassium and important trace elements such as iron, manganese, copper, and zinc (Morrison et al., 2009). Due to the coarse texture of the soil, water retention rates are very low, with most of the organic matter running off instead of being absorbed as nutrients in the soil (Falkland, 1997). Poor soil makes sustainable agriculture on the island very difficult (with the exception of copra), and also limits the production of traditional Pacific subsistence plants like taro (Morrison et al. 2009). The geographical remoteness of the island makes the continuous importation of food unsustainable.

Few species of plants and animals naturally live on Kiritimati because of its remote geographical isolation, overall low level of nutrients, and harsh environment. There are an estimated 83 indigenous plant species in Kiribati, none of which are endemic (Thomas, 2003). The forest cover on Kiritimati is comprised of three small stands of Pisonia grandi of about 10 meters in height. However, the most dominant plant throughout Kiritimati is Scaevola taccada, a small flowering bush that tolerates brackish areas. During the colonial period, the little diversity of island flora that existed was further reduced when a system of monoculture was established for the production of copra. Copra now continues to be a major export of Kiritimati, with coconut palms covering about 5,200 hectares (UNEP).

Figure 3. Coconut Palms, David Siu 2011

Kiritimati is home to a large population and great variety of tropical seabirds. A total of 37 bird species have been sighted on the island, while about 20 species are known to breed there. Kiritimati has only one species of land bird, which is also its only endemic species: the Christmas Island Warbler. Kiritimati is a vital nesting ground for thousands of seabirds. This was formally recognized in December 1960 when the entire island was declared a bird sanctuary (UNEP).

There are no native mammals on Kiritimati. Polynesian Rats are the only non-feral mammal found on Kiritimati, probably having been introduced to the island by early Polynesians (UNEP). These rats, in addition to feral cats, often feed on the eggs and young of seabirds. This has had a significant negative impact on the seabird population (VanderWerf et al).

Reptiles on the island include Mourning Geckoes, Snake-eyed Skinks, and Stump-toed Geckoes. In addition, Kiritimati often plays host to nesting Green Turtles. A variety of invertebrates including Coconut, Ghost, and Land Hermit crabs also inhabit the island (UNEP). Overall, the biodiversity of both flora and fauna is severely restricted by its remote geographical location. Anything that might have drifted over would have had difficulty surviving and thriving on the islands due to the lack of nutrient-rich soil and freshwater. Most of the current flora and fauna present on the island is thought to have been introduced by ancient Polynesian travelers who used the island as a temporary resting area (Piazza and Pearthree, 2001).

Figure 4. Birds, David Siu 2011

Aside from Kiritimati’s anthropogenic problems of pollution and the overexploitation of fisheries, the future of the island is further stressed by rising sea levels. The Republic of Kiribati is located in the dry belt of the equatorial oceanic climatic zone and has an arid climate. Although the island’s geographical location within five degrees of the equator provides two wet seasons due to the Intertropical Convergence Zone (ITCZ), the close proximity to the equator also leaves Kiribati highly susceptible to El Niño Southern Oscillation (ENSO), and it consequently suffers from only sporadic rainfall. On average, the island of Kiritimati receives 873 millimeters of water each year but this fluctuates anywhere between 177 millimeters to a maximum of 2,621 millimeters depending on La Niña or El Niño conditions (Morrison et al., 2009). Further exacerbating the problem is the evapotranspiration rate which often exceeds the annual rainfall (Morrison et al., 2009).

The island’s lagoon has a northwest channel that connects to the ocean and a network of hyper-saline lagoons and lakes in the southern part of the island (UNEP). The saline lagoons and lakes range from a salinity of nearly freshwater to 150 ppt and starkly contrast to the barren landscape with pastel colors of bacterial mats (Saenger et al, 2006). Despite the main lagoon’s relatively large size, it is quite shallow and is becoming increasingly polluted in the northwest corner near the town of London because of expanded development and a lack of anti-pollution enforcement (Walsh, 2011). Due to the unreliable precipitation, nutrient deficient soils, and saline brackish water lens, agriculture is restricted and island life is therefore dependent on the surrounding waters and coral reefs.

The fisheries areas surrounding the northern sections of Christmas Island are currently in a state of degradation due to an over-exploitation of reef fishes (Walsh, 2010). The inherent enjoyment of fishing as well as the importance of fish as a means of sustenance has led to an overall decline of reef fish near populated areas. In hopes of reducing the fishing pressure, the subsidy for growing copra was enacted, but it ironically increased fishing activity due to extra leisure time (Walsh, 2011). Due to the extraction of larger herbivorous fish and nutrient enrichment near London, an abundance of macroalgae has grown inshore.

Despite British and American nuclear testing on the southern end of the island, the reefs on the southern parts of the island are still relatively pristine and untouched due to limited access to the southern border. Since Kiritimati as a whole is a wildlife sanctuary for seabirds, there are also preliminary plans for the establishment of a marine protected area surrounding certain areas of coral reef (UNEP).

While developed countries disproportionately emit large amounts of carbon dioxide, less developed countries comprised of low lying coral atolls are unfortunately put at a high risk of inundation due to rising sea levels as a result of climate change. The majority of climatologists support the concept of climate change in which average global temperatures are increasing an average of 1.8 - 4°C by 2099 (ICCP, 2007). Due to the increased temperatures, the polar ice caps are melting, resulting in a slight increase of sea level each year. The combination of melting ice caps and the expanding warm water is predicted to increase the global mean sea level by 88 centimeters in the next 88 years, with local variations (Locke, 2008). With Kiritimati’s highest point a mere four meters above sea level, entire communities are at risk for flooding. As Kiribati lacks a proper self-sustaining economy, the country also lacks proper infrastructure, such as sea walls, to protect communities from rising sea levels. The gradual increase of sea level will cause coastal erosion and the progressive salinization of any potable water sources on the island (Locke, 2008). This imminent threat is a much higher priority than initially thought, and Kiritimati is already experiencing both direct and indirect consequences (Locke, 2008). Many inhabitants of the Republic of Kiribati are migrating away from smaller low lying coral atolls to larger and more populated islands such as the capital of Tarawa (Locke, 2008). The increase in urbanization in more populous areas is often ill conceived and exacerbates the over-exploitation of near-shore marine fisheries. The islands are so vulnerable to sea level rise that the International Institute for Environment and Development has ranked Kiribati as one of the top ten most vulnerable countries in the world (Morrison et al., 2009), and its future remains uncertain (Locke, 2008). Kiritimati’s lack of permanent settlement in the past reflects the severe lack of natural resources available to sustain life over time (Piazza et al. 2001).

As pressures on the marine fisheries continue to reduce fish stock, and as climatic disruption brings a consequential increase in sea level, Kiribati may once again be uninhabitable for sustainable living in terms of modern lifestyles. Unlike many of the other productive and lush South Pacific islands, Kiritimati’s environment is particularly barren and arid. The island’s geographical location in the equatorial dry zone in combination with its nutrient-poor soils and growing population has resulted in the over-exploitation of already limited natural resources. This, in addition to imminent sea level rise taxes the current population on Kiritimati and leaves their future uncertain.

FIGURE 5. BEACH, David Siu 2011

David Siu, Rhodes College
Ariane LeClerq, Carleton College
2011


 

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