High levels of oxygen are available on the upper layers and can be used as an electron acceptor. which organisms would you expect use other electron acceptors?

Diverse community of interdependent microbes; enriches for muds anaerobic microorganisms by mixing in ingredients to provide food and other substrates for bacteria to use. what does ... use sulfate rather than oxygen gas as terminal electron acceptor, thereby generating high concentrations of hydrogen sulfide at bottom.

They both have rock surfaces