You do NOT need a reservation for breakfast or lunch as these meals are primarily buffet style.
Dinner at 8 of the A La Carte restaurants require reservations. Two of the dinner locations, La Plaza buffet and Star Rock Café, do not.
Note: During your stay at conference you are allotted 4 A La Carte dinner reservations maximum. These may be used at any of the A La Carte restaurants. In the Iberostar hotel app you will see which restaurants require reservations. Your remaining dinners are at the buffet or Star Rock Café which do not require reservations.