Dead Man's Fingers
Here's one to add to the invasive species list, though I'm not sure if on this beach it is. It's somewhat unclear to me if it's invasive on the Pacific coast of the US or not, but it is on the Atlantic. It is thought to have originated in the oceans near Japan.
''Codium fragile'', known commonly as green sea fingers, dead man's fingers, felty fingers, forked felt-alga, stag seaweed, sponge seaweed, green sponge, green fleece, and oyster thief, is an invasive species of seaweed in the family Codiaceae.