I don't think having a degree in marine biology is important at all. If you are going to get a degree, Business is FAAAAR more useful when it comes to running a business.... You can have all the fish knowledge in the world, but if you don't know how to get/keep yourself in the black, who cares?? It's a business first and foremost. Yes, it's important to know your product, but there isn't anything you are going to learn about aquariums studying marine biology that is going to make you more successful than what you can learn yourself over the next 10-15 years.
Oh yeah, and make sure you have good credit. You're going to need it for that $200,000 loan. Number one reason new businesses fail is a lack of start up capital, so make sure that you get enough for both the business AND your personal needs. Get as much money as you can.