User blog comment:Unownshipper/Flora and Fauna of Rapture/@comment-1592487-20131106045727/@comment-6024608-20131106082119

Farming/harvesting (plants would have to be the bulk) would be done inside (tunnels in seabed?) of more normal foodstuff (kelp and fish only gets you so far)

with artificial light (lots of cheap power/heating from the geothermal...)