Staghorn (seen here) and elkhorn corals are listed as Threatened under the U.S. Endangered Specis Act, as their numbers have fallen catastrophically due to disease. Listed in 2006, they were the only coral species under protection until 2014, when 20 other coral species were listed as threatened for a total of 22 species. Both staghorn and elkhorn coral are found in Caribbean waters and reproduce when bits of their branches break off and reattach to a hard surface. They also can reproduce through spawning, but only do so on a few days each year. See more endangered ocean species in our slideshow.