My two cents:
Aquaculture is a broad term, and mariculture is a specific type of aquaculture.
aquaculture \aquaculture\ adj.
1. the cultivation of aquatic animals, such as fish or shellfish, or of plants, such as seaweed, in a controlled and sometimes enclosed body of water. The term includes use of either salt or fresh water. It is a form of agriculture, but under water. [PJC]
Source: The Collaborative International Dictionary of English v.0.48
Note the "sometimes enclosed"
aquaculture
noun
rearing aquatic animals or cultivating aquatic plants for food
Source: WordNet (r) 2.0
I don't really think anyone is being misleading by using the term aquaculture.
Now on a different note. I "heard" that there were some places in Viet Nam and the Philippines I believe that were collecting small wild clams off reefs, then bringing them in and keeping them under their control (pools/cages) for a while to let them get bigger - then selling them as aquacultured clams. That in my opinion is very misleading, as the clams originated from the reefs...