That's why these new ecosystems were named methane seeps when they were first discovered. Since then, scientists have learned that methane does not always "seep" out of the seafloor because it can also be exposed by earthquake-induced landslides.
Seep communities can also occur in other settings, in association with hydrocarbons; such as, petroleum oil, tar, or asphalt.
When deep-buried methane moves upwards towards the seafloor, it is consumed by microbes that interact with other bacteria to produce sulfide. Although sulfide, which smells like rotten eggs, is usually highly toxic, it supports a group of animals that are specialized in dealing with chemical environments known as chemosynthetic animals, similar in thier body organizations to the animals found at hydrothermal vents.
The fauna attracted to the methane seepage form what is known as "true animal bases" on a landscape of otherwise relatively featureless, homogeneous sediment in the deep sea.
First, bacteria graze on the chemical fluids (methane and sulfide) that seep out of the seafloor. Then, special clams and mussels arrive that house symbiotic bacteria that can harvest the chemicals to produce energy for their hosts.
Also present at seeps are tubeworms with sulfide-consuming bacteria; some of which have very long roots that can reach a meter down under the seafloor to look for sulfide.