“primarily oatmeal, pasta and rice.”
All which requires copious amounts of water, and heat to boil it with. Is cooking such in saltwater a nutritionally good idea? else how much pure water did they have? Maybe a desalination system on board, but what resources limit its use? Whither fuel?
A lot of foods are very delicious when boiled in seawater. Try boiling some corn on the cob in seawater some time. Delicious. I'm sure rice and pasta would benefit too. After it boils, there is no concern about what might have been living in it.
The only potential downside to cooking in salt water is kidney failure.
If you had read the rest of the sentence you posted ...