OrionN:
You should do some research on this before posting so emphatically. A simple search or knowledge of clams would have told you that you are wrong. There is no doubt that Clams absorb Nitrates and phosphates. There is much scientific literature and experience about it. Clam farmers add nitrates to their cultures to increase growth.
http://scholar.google.com/scholar?hl...es&btnG=Search
By your reasoning, bacteria can not absorb nitrates either because they are non-photosynthetic, and yet some eat nothing but.