Weeell... I know a few people with this name here in Ireland, pronounced as you have spelled it. The spelling here though is Muiriosa and is a name made from putting together Mary and Joseph in Irish.(the first syllable is slightly more of a mur sound but very similar~) A friend loved this as her name although she did have to spell it(and usually explain it) for everyone. But then again shes in her thirties and we all had quite boring names.
I would have thought Marisa was a completely different name.