The Gulf Stream bathes the Caribbean in warm water, shown by the deep red and yellow.
Warm waters are one requirement necessary for tropical corals to build massive reefs.
But if it gets too hot, the corals can begin to bleach, expelling the photosynthetic algae, called zooxanthellae, that live in the coral's tissues and give them the extra boost to make their skeletons. This image shows sea surface temperatures. Reds and yellows show warm water, blues and greens represent cooler waters. Notice the swirling eddies in the North Atlantic. Reefs protect the islands by providing a barrier between land and the rough open seas and reducing the damage from hurricanes and storms.