Methane gas, trapped deep within the Earth's crust, can slowly leak from cracks in the seafloor known as methane seeps. While we would never consider methane as food, in the deep sea where there is little light or resources, microbes have evolved to turn methane into energy and live off of it. And where there are microbes, there are often other animals—such as tube worms or mussels—that eat those microbes. In this photo, bubbles of methane gas rise through a mussel bed in the Gulf of Mexico.