Finnish Defence Forces' tests on similar Iceland moss (Cetraria islandica) suggest that lichens could used for food as 100 g of fresh lichen contains c. 183 kJ or 43,6 kcal. However these also have great intake of lead and other heavy metals from the air and ground; e.g. specimens collected during the 1970s from the Finnish wilderness contained up to 30 000 μg of lead per kg, that's over 30 times the safe limit.
However if you should try making food out of them, the moss must be soaked up to five days on 0,5 % - 1 % alkali and then washed, dried and pulverized.