Exactly. The anaerobic ones "breath" sulfur instead of oxygen and they make the "stink of low tide" form sulfur excretions. Same same in the holding tank.
If you have the luxury of adding a fresh water blivet near the head, and IF you can use fresh water to flush the head (and backflush the inlet hose) you'll also find there's much less stink. Decomposition of critters in the sea water also causes a lot of odor. If you can spare an extra fresh water source (a flex bladder is fine) to use rather than raw water to flush the head, all the better.