The Maldive Islands are a series of coral atolls built up from the crowns of a submerged ancient volcanic mountain range. All the islands are low-lying, none rising to more than 6 feet (1.8 metres) above sea level. Barrier reefs protect the islands from the destructive effects of monsoons. The rainy season, from May to August, is brought by the southwest monsoon; from December to March the northeast monsoon brings dry and mild winds. The average annual temperature varies from 76 to 86 °F (24 to 30 °C). Rainfall averages about 84 inches (2,130 mm) per year. The atolls have sandy beaches, lagoons, and a luxuriant growth of coconut palms, together with breadfruit trees and tropical bushes. Fish abound in the reefs, lagoons, and seas adjoining the islands; sea turtles are caught for food and for their oil, a traditional medicine.