Sea Animals
Birthday Party Collections

You do not have a link list with a handle set to under-the-sea-birthday-party-collections, or you do and it's empty. Go ahead and create a link list called Sea Animals
Birthday Party Collections
on your Navigation page and populate that link list with links that point to collections, to see collections listed here. Make sure the link list also has a handle set to under-the-sea-birthday-party-collections.