I am going on my 1st cruise in Oct. and have been reading up on everything I can find,I remember reading that if you are on the CCL that they do have a plan that you can get to the Seaquarium that includes transportation.
I did the Miaimi seaacquarium last year and it was really nice. It was about $25 per person plus you can download a coupon for about $3 off. We got there at 10am and were done by 2pm this was in Oct. I hear they have a nice swim with tthe dolphins too.