This is a common encrusting compound tunicate that is commonly found along docks in the Pacific Northwest. Similar to other tunicates it grows on rocks, barnacles, bivalves, as well as the exoskeleton of a number of crab species. Though it may appear like a gray goo covering kelp that is growing along docks, it can be quite beautiful when viewed under a dissecting microscope.
Photos and Video by Noah Elkink
Lamb, Andrew, and Bernard P. Hanby. Marine Life of the Pacific Northwest: a Photographic Encyclopedia of Invertebrates, Seaweeds and Selected Fishes. Madeira Park, BC, Harbour Publ., 2009.