Steve Austin wrote in
news
They are not using photosynthesis...they are using chemosynthesis.
Chemosynthetic bacteria use not the sun, but chemical energy to
make food. They use hydrogen sulfide gas coming from the vents in
the same way that plants use carbon dioxide and water.

Do a google search for chemosynthetic bacteria for more
information... -Scott

Recent discoveries have shined light on the subject. Apparently there
is also a bit of light there, and it is being taken advantage by
organisms to make biological energy using photosynthesis.

It is all over the science news this last week or so.

Sean