You know how when you go snorkeling, the guide tells you not to touch, breathe on, or even think about getting anywhere near the coral because it's really sensitive and also a great marine resource? Well, it's all true, but on a macro level, humans haven't been paying attention to those instructions and instead have been spraying the coral down with water contaminated with our waste. So basically we have been POOPING ON THE CORAL, which is kind of the opposite of not touching it. And human waste infects coral with something called white pox disease, which causes lesions and has led to a 90 percent decline in elkhorn coral, a key player in reef building.
Scientists knew for a while that a particular bacteria was responsible for the disease, but that bacteria is found not only in human intestines but those of other animals, too. Each strain of the bacteria has a particular genetic signature, though, and when scientists matched the bacteria hitting the coral with samples from all sorts of animals, they found that the only one that matched up was ours. Busted, reef-poopers.
There's a relatively simple fix to this problem: people in places like Florida need to stop building leaky sewage tanks in porous ground. According to Science, once Key West built a wastewater treatment plant, the coral did much, much better.