In some countries, medicinal plants and animals provide most of the drugs people use, and even in technologically-advanced countries like the USA, half of the 100 most-prescribed drugs originate from wild species. A square kilometre of coastal ecosystem such as mangroves forests can store up to five times more carbon than the equivalent area of mature tropical forests. But these areas are being destroyed three to four times faster than forests, releasing substantial amounts of carbon dioxide into the atmosphere and the ocean, and contributing to climate change. Tourists spend billions of dollars every year to watch birds or whales, or witness wildlife spectacles such as the great annual migrations in the Serengeti ecosystem of Tanzania and Kenya where 1.5 million wildebeest, 500,000 Thomson’s gazelle and 200,000 zebra cross the plain. Overfishing has reduced some commercial fish stocks by more than 90%.