South of the equator and at the 180th meridian are coral atolls and reef islands in the Pacific Ocean. Atolls have sandy barrier islands surrounding a shallow lagoon. They are the tops of volcanoes that do not quite make it above water level, and over geologic time corals have built up enough to make them rise above sea level. All are in the Western Polynesian tropical moist forest ecoregion.
The islands were visited by ships of the U.S. Exploring Expedition in 1841, after they had discovered land in Antarctica and were heading to Hawaii and the Pacific Northwest. The islands were noted as being well-covered with coconut and other trees. One island was mapped as 13 miles long and another as 8 miles long (Wilkes, 1844).
Islands such as those that make up the entire countries of Tuvalu and Kiribati are considered vulnerable to rising seas related to global warming (Nicholls and Cazenave, 2010). However, geologists think it is possible that sandy islands are capable of growing and rising as the sea level also rises. This assumes that sea level rise is gradual as predicted. During periods of high seas such as during storms, waves will wash over these islands. But instead of eroding the land away, the waves will likely deposit sand from coral. Reefs grow up to 10 to 15 mm per year, faster than sea level rise. As long as the reef remains healthy, a reef island can keep up with sea level rise. Unfortunately, poor shoreline management and human activity also affects some parts of these islands (Pala, 2014), and this can combine with sea level rise to drop inhabited shorelines below sea level.
Forests of the Western Polynesian tropical moist forest ecoregion are dominated by Pisonia (Nyctaginaceae), Cordia (Boraginaceae), Tournefortia (Boraginaceae), Scaevola (Goodeniaceae), and Morinda (Rubiaceae). Common also are Calophyllum (Calophyllaceae), Pandanus (Pandanaceae), Hernandia (Hernandiaceae), and Ficus (Moraceae). Drier areas have herbaceous grasslands. The Funafuti Conservation Area consists of 33 km2 of ocean, reef, lagoon, and six islets (Government of Tuvalu, 2020). The islets are a nesting area for green sea turtle, a colony of black noddy, and terns, sandpipers, shearwaters, boobies, and tropicbirds. The Pacific imperial pigeon and long-tailed curlew use land habitats.
- Arorae, Gilbert Islands, Kiribati (S2o38’ E176o49’), an atoll 9 km in length. At the north end, navigational stones provide direction for trips to nearby islands (Republic of Kiribati, 2012a).
- Beru, Gilbert Islands, Kiribati (S1o20’ E176o0’), an atoll 14 km in length. The island features a lake with edible algae (Nein Tabuariki), and a lake with milkfish (Te nei ni man). Causeway construction has created additional lagoon habitat for fisheries. Environmental issues include drought, erosion, and marine overfishing (Republic of Kiribati, 2020b).
- Funafuti, Tuvalu (S8o31’ E179o12’), atoll and capital of Tuvalu, is comprised of about 30 islets surrounding a lagoon 18 km long and 14 km wide (tuvaluislands.com).
- Nanumanga, Tuvalu (S6o17’ E176o20’), is a reef island about a square mile in size with a fringing reef. In the center of the island is Vaiatoa lagoon. A cave used by people when sea level was much lower is located off the north shore (tuvaluislands.com).
- Nanumea, Tuvalu (S5o40’ E176o8’), is the northernmost atoll in Tuvalu, with an area about one square mile. A freshwater pond is in the southeast. There are 9 islets in an atoll about 12 km in length (tuvaluislands.com)
- Nikunau, Gilbert islands, Kiribati (S1o20’ E176o28’), a reef island 14 km long. It hosts landlocked, saline lagoons. Environmental issues include drought, coastal erosion, flooding, and depletion of sea cucumber. (Republic of Kiribati, 2012c)
- Niutao, Tuvalu (S6o7’ E177o21’), is a reef island about 1 square mile in size.
- Nui, Tuvalu (S7o13’ E177o10’), is an atoll with 21 islets about 1 square mile in size.
- Nukulaelae, Tuvalu (S9o23’ E179o51’), is an atoll with 19 islets, surrounding a lagoon 10 km long by 4 km wide (tuvaluislands.com).
- Nukufetau, Tuvalu (S8o0’ E178o23’, is an atoll with 35 islets surrounding a lagoon 13 km long by 7 km wide (tuvaluislands.com).
- Tamana, Gilbert Islands, Kiribati (S2o30’ E176o0’), is a 6-km-long reef island. It is noted as having a good freshwater lens but it is subject to saline intrusion. Drought, soil erosion, and overfishing are among the environmental issues (Republic of Kiribati, 2012d).
- Vaitupo, Tuvalu (S7o30’ E178o41’), is an atoll of 2 square miles, with 9 islets.
Republic of Kiribati, Office of Te Beretitenti. 2012a. Island Report 18. Arorae. http://www.climate.gov.ki/wp-content/uploads/2013/01/18_ARORAE-revised-2012.pdf (accessed June 21, 2020).
Republic of Kiribati, Office of Te Beretitenti. 2012b. Island Report 14. Beru. http://www.climate.gov.ki/wp-content/uploads/2013/01/14_BERU-revised-2012.pdf (accessed June 21, 2020).
Republic of Kiribati, Office of Te Beretitenti. 2012c. Island Report 15. Nikunau. http://www.climate.gov.ki/wp-content/uploads/2013/01/15_NIKUNAU-revised-2012.pdf
Republic of Kiribati, Office of Te Beretitenti. 2012d. Island Report 17. Tamana. http://www.climate.gov.ki/wp-content/uploads/2013/01/17_TAMANA-revised-2012.pdf (accessed June 21, 2020).
Government of Tuvalu. 2020. https://www.timelesstuvalu.com/ (accessed June 21, 2020).
Nicholls, Robert J. and Anny Cazenave. 2010. Sea-level rise and its impact on coastal zones. Science 328:1517-1520. DOI: 10.1126/science.1185782.
Pala, Christopher. 2014. Warming May Not Swamp Islands. Science 345:496-497.
Wilkes, Charles. 1844. Narrative of the U.S. Ex. Ex. During the Years 1838, 1839, 1840, 1841, 1842. Volume V. C. Sherman Publisher.