In lichen, do the fungi consume the oxygen produced by algae? Is the oxygen produced by algae in photosynthesis consumed by the fungi, specifically in marine lichens where oxygen is less abundant? I am wondering this because of a speculative evolution project.

Exchange of gases between lichen symbionts has been demonstrated for _Flavoparmelia caperata_. Note that this is a foliose lichen species, though the findings may be generalizable to marine lichen.

> We discovered the first evidence that photosynthetic O2 and respiratory CO2 mutually power the lichen symbiosis, together with the previously recognized exchange of Calvin-cycle sugars and water.

Ten Veldhuis MC, Ananyev G, Dismukes GC. Symbiosis extended: exchange of photosynthetic O2 and fungal-respired CO2 mutually power metabolism of lichen symbionts. _Photosynth Res_. 2020 Mar;143(3):287-299.