If I understand it correctly - then Biodomes are not just for food production, but also serve as part of the ecology of the space station.
That is to say that they serve other functions related to air and water purification, as well as green living space for the people on board.
Ultimately, the biodomes should exist in order for the station to be self-sufficient, and by no means an exporter of foodstuffs (except for small quantities for ships and outlying colonies).
Gran Canaria however, is a different matter. If the Zoners are to have a breadbasket - it would be this planet.