Field experiment observations

I'm about to wrap up my field experiment finally! Now that lots of mussels are drilled and empty, thanks to my dogwhelks, I've noticed many lined shore crabs that like to live inside them. I'm not sure if this will be a real result or if it's just a fun observation, but either way, it's cute.

We also found many of these gelatinous, salp-looking creatures in my cages this week. I don't know what they are, but they look really weird!

Pachygrapsus crab hiding in an empty mussel shell. I suspect larger empty mussels 

support more Pachygrapsus. Could this be an interesting result of my experiment?

Unknown gelatinous creature or substance found in my experimental mussel beds.