Clams consuming nitrates?

[Cheebs]

I was told that my crocea clams can feed off nitrates in the tank. Now, obviously I'll be keeping the nitrates as low as possible as usual, but I was just curious: Does having clams in the tank actually noticably HELP with keeping nitrates low, or is the amount they consume so minute that there is no noticable effect? Think of 2-3 clams in a 75 gallon tank.