People finally reached the Marquesas Islands to the east about 2,000 years ago. Human impact Migration brought great changes to island ecosystems. New crops and animals were introduced and forests were cleared for cultivation. Combined with the effect of tropical storms, these increased soil erosion. The sediment from erosion, in turn, smothered coral reefs.
Reefs protect many islands from the ocean and are rich in fish.
Most island ecosystems were badly degraded within 1,000 years of human settlement. The initial effect of European intrusion during the seventeenth century was to reduce human impact on the environment. Indigenous peoples, as elsewhere around the world, had no immunity to European diseases and many died, so cultivation and land degradation slowed. Native plant and animal species began to disappear and extractive industries ruined entire islands. Phosphate mining rendered much of the islands of Banaba and Nauru uninhabitable.