Almost every year, patches of shiny black or blue-black juvenile Mytilus* appear among the acorn barnacles on exposed rocky shores. Unfortunately, the patches don’t last long. Their vulnerability to predatory snails may partially explain their failure to persist.
*In 2018, when I composed this post, I thought the patches of juveniles must be Mytilus trossulus, but I’ve learned there’s a good chance they are M. californianus.
I updated this post on August 16, 2022, to reflect my uncertainty about the identity of the mussels.