Remember the mussel mortality event that I mentioned last week? (See posts called "Too hot" and "Too hot -- Part 2")
Eric Simons wrote an informative article about this event for Bay Nature magazine. You can read the article online here.
The photo above was taken on 18 June 2019 and the photo below was taken on 19 June 2019.
In the first photo you'll notice that some mussels are empty, but others still have their adductor muscles — the white muscle that holds the two shells together. In the photo below, the majority of mussels are empty, but in a few you can see the orange internal tissue (before it washed away or was eaten by other animals). At low tide, healthy mussels are normally closed up tightly, so you can't see the internal tissue or the inside of the shells.