A March low tide left this rock exposed and isolated in an otherwise featureless sea of sand. Low tide was not very low, but low enough for me to get close. Any stable rock on the beach is quickly populated by a dense and complicated encrusting community.
The most obvious inhabitants of this rock are the mussels, Mytilus californianus, and these in turn are inhabited with an encrusting layer of acorn barnacles, Balanus glandula. Acorn barnacles are crustaceans, at home in the high intertidal. You don’t even need to get your feet wet to observe them.
This view of the same rock exposes other members of the community, thatched barnacles, Semibalanus cariosus, giant green anemones, Xanthopleura xanthogrammica (tentacles retracted), and sea lettuce, Ulva.
Note: I updated the photos and lightly edited the text of this post on September 2, 2017. This little rock jutting out of the sand also appears in River of Sand, Sea Lettuce, Ulva, and Sand Cycles.