Barnacles and barnacle eaters

Tyee Spit serves as a breakwater between the mouth of the Campbell River and Discovery Passage, the main sea route between Vancouver Island and the mainland. Its shores, on the saltwater side, are mostly clean pebbles, scrubbed by the fast currents racing down the narrow channel; a few miles north, at Seymour Narrows, the currents reach up to 15 knots; here at the Spit, they run around 10 knots.

Sometimes, flipping stones on that shore, I find a crab or two, sometimes a limpet. But mostly, there are just more stones.

I happened to be passing a few days ago when the tide was unusually low, and saw that the lowest level of stones were rough, barnacled. I hurried down to look.

Here's one stone, and its community.

Swarming with life. Left to right; barnacle-eating nudibranchs, hermit crabs in periwinkle shells, maybe some snails in their own shells, barnacles, egg mass, Wosnesenski's isopods, "grape" seaweed.

Zooming in on the busy end. There are a couple more nudibranchs here, too. Click to see the individual eggs in the egg mass.

Look again at those barnacles above. The small, grey ones have an oval opening, and in the large, mostly dead ones (in this photo), the opening is approximately diamond shaped.

Acorn barnacles, Balanus glandula, and Little brown barnacles, Chthamalus dalli.

The grey barnacles (Little brown) is the smallest of our acorns. They are often found on rocks at the very top of the intertidal zone, where they may only be underwater and able to feed half of the time.

The larger, lighter, almost yellowish barnacles are the ones I see most often on the beach. Look closely; the plates enclosing the mouth lock together in a wavy pattern, somewhat like a W. (Or an M, if it's facing the other way.)

And here's one of the nudibranchs, Onchidoris bilamellata.

These tiny nudis (about as long as my fingertip is wide) eat the barnacles, drilling through the shell like a snail does. Underwater, they extend their two antennae and the feathery gills at the rear. Here, waiting for the tide to return, they are hunkered down, so that it's hard to tell which is the front end. (I think it's towards the right on this one.)

More low tide photos tomorrow.