actor bought blackadore caye , an unpopulated , private 104-acre belizean island , in 2005 for $ 1.75 million .
he announced friday he is now building a luxury eco-resort there to open in 2018 .
the resort will have villas over the water , artificial reefs with ` fish shelters ' and a nursery growing marine grass .
dicaprio plans to rehabilitate the area , which has been over-fished and suffers from sand erosion .
he is working with the nyc developers delos to build 68 resort villas and 48 private house .
they will cost between $ 5 million and $ 15 million each .