A thing that is rarely mentioned and I also do not see it mentioned in this article, is that these communities of organisms, even if they live in the dark, are

A thing that is rarely mentioned and I also do not see it mentioned in this article, is that these communities of organisms, even if they live in the dark, are sustained in a great proportion by the free oxygen dissolved in the water, which comes from above, from the phototrophic algae and plants. Most of the energy that is used for chemosynthesis by the bacteria upon which all others feed, comes from the oxidation with free oxygen of the hydrogen sulfide that comes out from the oceanic vents. Only a small part of the bacteria present there are methanogens, which use free dihydrogen coming from the vents and carbon dioxide, to make methane. Except for the methanogens and for the even less abundant acetogens, most bacteria living there still depend on the solar energy captured by algae and plants. The same is true for all the animals present there, which feed on bacteria or on each other. So if a giant meteorite would hit the Earth, preventing photosynthesis for some years, that could still wipe out most of the members of these chemosynthetic communities from the bottom of the ocean, because the water around them will be depleted in oxygen, killing even most of the bacteria. Of course, at least most of the anaerobic bacteria will survive.