Chemosynthetic bacteria means bacteria that can make chemical things (synthetic). Basically any bacteria are chemosynthetic - they all product different chemicals as part of their metabolism. There are methanogens that produce methane gas, there are photosynthetic organisms that produce oxygen (like plants, and the ancestry of plants), others can produce nitrogen gas, like those bacteria that live in nodules on legume plants. Other bacteria can produce acids from fermentation like proprionic acid which gives Swiss cheese its nutty flavor. So lots and lots of bacteria are chemosynthetic. It just depends on what you want to produce.
In the dark.
There are many decomposers in coral reef but heres one a fan worm.The Main Decomposer is bacteria , a bacteria can live there because of chemosynthisis.There are many thousands of other decomposers which are in coral reef of course but heres a few fungi, worms, slugs, snails, starfish, crustaceans. And it is pretty easy to find some you should go see coral reef underwater.