Hi
We went to the Zoomarine last year from Albufeira,we went to the reception desk in the hotel and they sold tickets, but as we wanted to go that day he told us to go and just get on the zoomarine bus.The girl did ask for our tickets as we were getting on the bus,but when we told her we didn't have any she said it wasnt a problem just pay when you get there.
We went in June, it might be different if you are planning to go in July or August when its busier though.