Coral reefs are the largest organic structures on Earth, yet they're created through a symbiotic relationship between creatures about 3 millimeters long. Learn more about the the world's coral reefs (and how to protect them) in this episode.Learn more about advertising on the HowStuffWorks podcasts at www.howstuffworks.com/advertisers.htmAnd to learn about your ad choices when listening to podcasts, visit https://www.howstuffworks.com/privacy.htm#ad-choices
