The red abalone is a gastropod (univalve) having a large,
oval shell shaped like a shallow bowl. It is the largest of California's marine
snails and one of several abalone species inhabiting the California coast. The shells of some archaeological
specimens are close to 30 cm in length, and lengths around 20 cm are common.
Most of the abalone's body under its shell consists of a "foot" for
attaching itself to a rock surface and sometimes for locomotion, although a
mature abalone generally resides in one spot. Abalone feed on algae, and the
red or coral color of the outer surface of a red abalone shell (the shell's
epidermis) results from consumption of red algae.
The interior surface of the abalone shell (to which its soft tissue
is attached) is mother-of-pearl, or nacre. Its relative smoothness
and high luster have made it an attractive material for making
ornaments in both prehistoric and historic times.
Water taken in by the abalone and passed over its gills exits
through a row of holes (apertures) along one side of the shell
(although the hole nearest the front (anterior) edge of the shell
may be used for water intake). As the shell grows larger, new
and larger holes are added and the old holes on the opposite (exterior)
end of the row are plugged with nacre. Typically, four such holes
are open, but the holes filled with nacre are easily seen on the
shell.
Today, most red abalone live mainly in subtidal waters to depths
of more than 20 meters, even along the central California coast,
where historically they also occupied the intertidal zone in significant
numbers. Their geographic distribution extends from Sunset Bay
along the Oregon coast southward to Bahía de Tortuga in
Baja California. The largest concentrations, however, are in central
California.
Shorepicking by visitors to the coast keeps the numbers of red
abalone in intertidal waters low, and because of intensive harvesting
by commercial abalone divers over the last 30 years, their numbers
in subtidal waters anywhere along the California coast are much
lower than they were earlier. Sea otters living along the Monterey
County coast also are a significant predator; they use rocks to
smash the shell of an abalone, thus exposing its soft tissue.
If an abalone is able to avoid its predators, it may live to be
more than 20 years old.
References
Abbott, Donald P., and Eugene C. Haderlie, 1980. Prosobranchia:
Marine Snails. In Intertidal Invertebrates of California,by Robert H. Morris, Donald P. Abbott, and Eugene C. Haderlie,
pp. 230-307. Stanford University Press, Stanford. (A discussion
of red abalone appears on pp. 232-234.)
Cox, Keith W., 1962. California Abalone, Family Haliotidae.California Department of Fish and Game, Sacramento.
Howorth, Peter C., 1978. The Abalone Book.Naturegraph,
Happy Camp, California.