Micronesia is an island country in Oceania. It consists of four states – from west to east, Yap, Chuuk, Pohnpei and Kosrae – that are spread across the western Pacific. Together, the states comprise around 607 islands that cover a longitudinal distance of almost 2,700 km just north of the equator. They lie northeast of Indonesia and Papua New Guinea, south of Guam and the Marianas, west of Nauru and the Marshall Islands, east of Palau and the Philippines, about 2,900 km north of eastern Australia, 3,400 km southeast of Japan, and some 4,000 km southwest of the main islands of the Hawaiian Islands.
The major coastal communities are mangrove forests, seagrass beds, lagoons and coral reefs, biologically and physically linked. About 300 species of coral, 1000 species of fish and 1200 species of mollusks are recognized in Micronesia. In the mangrove forests there are shrimps, crabs and fish, as well as birds that feed on them. Seagrass meadows appear offshore following the mangroves. The lagoons provide food for the reef inhabitants and contain various kinds of plankton. The biodiversity and complexity of the coral reefs increases markedly from east to west, with 150 species of hard coral at Kosrae, 200 at Pohnpei and 300 at Chuuk. Coral productivity in this area is among the highest in the world, absorbing about 2500 grams of carbon per square meter per year, against 2200 grams in the tropical forest and 125 grams in the open sea.
Inland, from the tidal zone to the top of the mountains there is a varied range of vegetation, cloud forest, upland, palm, plantation, areas dominated by climbers of the genus Merremia, savannas, native secondary forest, fragments of introduced trees, cultivated areas, freshwater swamps, swamps of the palm Nypa fruticans, atoll forests, forests in rocky areas and beaches. There are about 1230 species of ferns and flowering plants, of which 782 are native, including 145 native fern species. On Pohnpei Island, there are about 750 plant species, of which 110 are endemic. Another 457 species have been introduced.