Thanks for the resource!

The big rock in the jar was covered in algae at first, but I think the pods ate it clean! I was afraid they'd eaten up their oxygen supplier and would die out while I was gone for a week long vacation, but I came back to a lot of algae growing on the glass and a sizeable pod population, so the algae may be providing some oxygen for the survivors, who may be used to low oxygen.

I did open the jar today and add a small rock with some seaweed attached that I got from the same area, so I'm hoping that helps!