The marine center is a great spot. The nice thing is that it's not a zoo. The animals aren't in small cages or overcrowded pools. They are very obviously well looked after, and you can tell the staff really cares about them.
One of the best parts of the aquarium is the seals. They have had the same seals for ages, and every year, they have a pup. They also have huge tanks of fish, snakes and lizards, etc.
Depending on how many are travelling with, you may be better to buy a family pass. It's $35, but when you figure that adults are $7, and kids are $4.50... Whatever you wind up paying, it's worth it to see these animals in what is probably the closest thing to their natural environment possible.