Mussel Carnage

Last Sunday, we "tidepooled" at Cape Kiwanda. The tidepools here are actually sandstone rocks covered by beds of mussels, barnacles, and countless other organisms.


Life is tough in the inter-tidal zone, and for me, viewing mussel beds is similar to watching predators stalk and consume their prey on the Serengeti, but on a much smaller and slower scale.

A few feet of sand had been deposited on the beach since the last time we here, burying the lower layers of the mussel beds. The largest mussels are usually found high above the water at low tide, where they have grown old in the absence of predatory seastars that dry out if they climb too high. The newly deposited sand had lowered the large mussels' elevation, however, and a feast was on!


Several seastars were in the process of wrapping their arms around the mussels, opening the shells, and digesting the contents from the inside-out.


Sarah spotted someting strange sticking out from an opened mussel shell. As we looked close, the thing appeared segmented and worm-like. I tapped it on it's side and it withdrew its head from the shell.


It was a carnivorous mussel worm (Nereis vexillosa) that was probably cleaning out what had been left in the shell by a seastar. It had two fleshy "fangs" and a bony "lip" that can apparently deliver a painful bite. These worms are abundant in mussel beds throughout the Pacific coast, but I had not seen one before.

California Mussels are my favorite tidepool creatures because the create an ecosystem with their presence.


Their shells are attachment sites for sessile creatures such as acorn and goose-necked barnacles pictured above. Worms and other free-moving animals find protection from predators and waves in the gaps between mussel shells. Some crabs even live inside the shells of mussels without bothering their hosts. Mussels: another example of valuable oceanside real estate!

Beach Finds

As usual, we spent Independence Day weekend in Pacific City. The weather was cold, gray, and wet, a nice break from the heat and humidity of Hillsboro.


On Friday, we brought Andie to the tidepools of Cape Kiawanda. She had a great time jumping on rocks and seeking interesting smells.


While Sarah likes to find rare creatures such as chitons and nudibranchs hidden among the more common residents, I am most interested in two of the main players in the tidepool saga: seastars (Pisaster ochraceus) and California mussels (Mytilus californianus). These species seem to be locked in a never-ending battle for survival. The seastars are always looking to have mussels for their next meal, and the mussels seek spots on the rocks that become too dry at low tide for the seastars to survive.


We found a seastar that had just finished one mussel and was holding on to another for its next course. The first mussel had been opened by the star's tube feet, its contents digested by the external stomach of the predator. Life seems tough for mussels, but they are capable of moving along the rocks to find places that are safe from seastars.

We also surveyed our beaches for dead seabirds.


At Bob Straub State Park, we found our second black-footed albatross of our dead bird counting career. It was a molting adult that was fairly intact. We tried to get Andie to pose near it for a size comparison, but she was not interested.


Along the survey routes, we also found a large number of pelagic goose barnacles (Lepas anatifera) stuck to washed-up items such as kelp, driftwood, and bird feathers.


Pelagic barnacles are fascinating creatures that live their lives at sea attached to floating debris until they drift ashore and die. I have seen some that are quite large, about eight inches long, but they can reproduce at small sizes to which they must grow quickly because their time at sea may be limited.


I imagine that forensic scientists would be interested in their growth rates to determine how long certain things had been out to sea.


I had never seen so many attached to so many things before this weekend. I am not sure if the bumper crop we observed is due to currents keeping all this debris at sea long enough to collect many barnacles before washing up or if their are unusually high numbers of barnacle larva out there seeking attachment sites.