Hi Chris,
There were some changes to search, but you will see this specific change go away very shortly.
However, if you want to strictly control your searches then I recommend changing that canned URL you have to a keyword query. Instead of q=marine ecosystems -> keyword=marine ecosystems. This will bring up an exact search for everything tagged marine ecosystems.
Just curious, are you still seeing the most relevant search results come up on top and then seeing extra results below, or something different?
Daniel