Might be a very empty marine park if you are building it in Planet Zoo lol
Why? It's already relatively big. I can't show Pictures of course because my PC is still dead (having no Money sucks) so I'll describe it as good as I can from Memory.
Welcome to Marine Center Hawaii. After entering you'll be immediately greeted by decorative Water Displays, surrounded by lush tropical Foliage. Enjoy the beautiful Flowers and impressive Palm Trees.
Our first Animals you will see on the Tour, are the Grey Seals and Saltwater Crocodiles. If you go further to the left, you will find the only Freshwater Animals in the Park. The Hippopotamus. In the Middle of the Park is our Polar Bear Dome in which Guests can observe the biggest Land Predator.
There are also Diamondback Terrapins somewhere I think and it might be that I've also used the Starfish Blueprint I've created once and maybe also a Octopus Blueprint from the Workshop. There's also a huge Dolphin Tank (I think more than double the Size of the Polar Bear Dome) but of course there aren't any Animals inside yet.
There's also a Coral Breeding Tank but that's in the Backstage Area
Ok, I realize, currently there aren't really that many Animals but due to a nice Layout and nice planted Areas it still doesn't look that small.
Things that were planned to come to the Park, are:
-a Room that is connected to the Polar Bear Dome that will include King Penguins and Grey Seals. The Grey Seal Enclosure will have a Window so Guests can see them from inside the Polar Bear Dome and also take a Look at a educational Sign where they will learn how Polar Bears hunt their Prey
-Relocation of the Grey Seals to the mentioned Indoor Area and Introduction of Sealions into the Enclosure because they can cope way better with the tropical Heat
-The African Penguins will probably get their own Enclosure outside. It is also tempting though to create a Mixed Species Penguin Colony
Don't know if I forgot anything important that is located in the Park or was planned to be added