This video says about itself:
Wildlife of Exuma Island, Bahamas – Lonely Planet travel video
From New Scientist:
Bahamian paradise built by bacteria using Saharan dust
13:40 28 July 2014 by Flora Graham
In this NASA satellite image from 2009, it is possible to see how the many islands of the Bahamas are actually the highest points of distinct areas where the sea is shallow and turquoise.
These turquoise waters mark the top of the Bahama Banks – underwater columns of coral reef limestone more than 4500 metres tall that have formed over the past 100 million years. It was thought that tiny plants and animals generate the vast amounts of carbonate that make up the towers, similar to how coral reefs are formed. But the surrounding sea is poor in nutrients, so what would have sustained them is a mystery.
Now researchers including Peter Swart from the University of Miami’s Rosenstiel School of Marine and Atmospheric Science in Florida are showing that photosynthetic cyanobacteria may actually have done much of the construction.
Cyanobacteria are involved in the precipitation of calcium carbonate in the sea, but they would have needed an enormous amount of iron to do their work. This could have been provided by the dust that blows across the Atlantic from the Sahara.
There are characteristic traces of iron and manganese in recent carbonate sediment on the banks, pointing to their Saharan origin. So the team suggests that the Bahama Banks are being built up by cyanobacteria and may also have been in the past.
The results of this research are here.