Barnacle Wall

The barnacle wall is a vertical low intertidal bedrock wall facing east. It is approximately 1 meter high and 3 meters long.  Tidepools have formed at the base of the wall, though at low tide many pools may dry out.  This wall is accessible during very low tides (-3.0 ft.) and may not be exposed during most of the year.

The upper two-thirds of the wall is mostly covered in thatched barnacles (Semibalanus cariosus). The lower one-third has few barnacles and more algae.  Large kelp was entirely absent, and other kelp was sparsely distributed.  The lack of algae and a low diversity of animals (compared to Lindsey's Crevice) may be due to the direct wave action that this wall receives. With no barriers to deflect the waves, plants and animals must be anchored to the wall. There is more diversity at the base of the wall along the tidepools; we found two sea slug species, black chitons, giant feather duster worms, and others.  The wave action appears to be deflected in this area, resulting in a more stable and less stressful environment.

We used quadrats to characterize a small area of the wall. A half meter by half meter quadrat was placed against the wall to count  species. The quadrat was further divided into 25 sections.  Using this grid helped to secure an accurate count of the animals. Sea lettuce (Ulva) covered 40% of the quadrat, and rockweed (Fucus) covered 5%. Thatched barnacles (Semibalanus cariosus) were found at a density of 1316 adult barnacles per square meter.  Other animals were rare in the quadrat: two limpets were found, along with one Nucella snail, one polychaete worm, one unidentified gastropod, and one black chiton (Katharina tunicata).

The dominant animals in this area are sessile as adults. Barnacles occur mostly on the upper two-thirds of the wall, where they remain fixed to the rock throughout their lives.  Barnacles have a free-living larval stage, the cypris larva, that swims freely using the cirri, or feet, in locomotion.  A larva's life is full of risks: predators can easily consume them and currents may take them far from shore. When barnacles settle, attachment is accomplished by antennal cement glands. These glands secrete an adhesive material that creates a permanent anchor.  By attaching themselves to the substrate, barnacles can live in areas that are vulnerable to wave action.

Thatched barnacles create a vertical wall of calcareous plates that protect them against predation and the trampling of curious scientists and students. Calcium is a commonly deposited material used for protection and structure in animals--from the tubes of marine worms, to the bones of humans, and the shells of oysters and clams. At first glance, barnacles resemble bivalves, with their thick white shells and sessile, or stay-in-place, lives. But barnacles are crustaceans, closely related to shrimp and crabs. Although they remain attached, some species of barnacles can still get around. The barnacle Coronula can attach to whales, hitchhiking rides throughout the ocean.  If you're not wearing boots, be careful walking on barnacles, because the sharp edges can easily cut skin and can even tear through thin shoes.

Restricted to life between a few hard plates, barnacles can not actively pursue food like other crustaceans. Instead, they have highly modified legs, or cirri, which extend through the shell to form a basket that combs through the water. The barnacle sweeps each side of the basket toward the center and downward, with the cirri acting as a scoop net. The cirri are then withdrawn into the shell and passed by special mouth parts, modified appendages that macerate the food particles before the barnacle swallows. On each cirrus there are tiny bristles, or setae, that capture food particles during the scooping stroke.
Barnacles aren't the only species found along the wall. The six-rayed sea star (Leptasterias hexactis) is also common.  Breeding clusters of at least a dozen form under rocks from December through March.  Reproduction in Leptasterias involves a highly-specialized brooding behavior.  The female releases eggs from pores on the upper, or aboral, side of the body at the same time that males release sperm.  The fertilized eggs are then moved via tube feet to the underside of the sea star. The larvae stick together, remaining under the sea star, which arches on the tips of its arms for about 40 days.  After this time she returns to her flattened position, but continues to brood for 20 more days.  The female keeps the eggs clean of foreign particles, and the young are abandoned when fully formed. The female does not eat for the entire time she broods. Her average life span is two years.


Animal species that can be found on the Barnacle Wall:




Next Page