Mytilus californianus (Conrad, 1837)
Very small individuals. Royal Palm
State Beach, Los Angeles
|(Photo by: Dave Cowles,
April 4, 1993)
mussel shell has
a thick profile and the anterior end (umbo)
is sharply pointed. It has strong radial ribs and irregular
growth lines. Parts of shell are often eroded. The periostracum
usually heavy and blue-black. The shell interior is
be slightly iridescent. Attach to rocks by byssal
How to Distinguish from
Similar Species: The
most similar local mussel species is the blue or bay mussel, Mytilus
trossulus. M. trossulus has a
smoother shell and is often
wider than M. californianus for its
length. Mature M. californianus
are distinguished especially by the strong radial ribs and irregular
growth lines, which M. trossulus does not
have. M. galloprovincialis
lives in the southern end of M californianus' range
CA south), and is nearly indistinguishable from M. trossulus.
Mixed clusters of M. californianus and M.
can be found on the open coast in southern areas. M.
seldom has much presence in the northern wave-exposed coasts, so
mussel beds are mostly M. californianus.
Range: Aleutian Islands
to Baja California
Depth Range: Intertidal
to 24 m
in intertidal zone
3 (lower midlittoral). Less common subtidally.
Clings to rocks
in wave-exposed areas, especially on the open coast.
History: A very common
inhabitant of the lower midlittoral (zone 3), where it often dominates
the substrate in waveswept areas (picture).
Specializes in living on large boulders and bedrock. Can move
from place to place by systematically breaking and remaking byssal
A filter feeder, filters 2-3 liters/hour. Spawns all year but
peaks in July and December in CA. A favorite prey of the
Small mussels are eaten by seabirds and by the oyster drill snails Nucella
nuttali, and Roperia poulsoni, although
it is less vulnerable to predation by snails than is M. trossulus
(Wootton, 2002). In central CA parasitic
isopods are often in the mantle cavity, as is also a pycnogonid and a
crab. May become poisonous in summer months through ingestion
dinoflagellates, especially Gonyaulax catanella
Although this species may experience high flow in the
due to wave action, byssal thread production seems to be limited to
of < 50 cm/s. Mussel aggregations sharply reduce water
them and make possible the production of byssal threads (Carrington
et al., 2008)
A study done on the related species Mytilus edulus
(from the Atlantic) found that the movements of individual mussels
correspond to a LÚvy
walk pattern rather than a ballistic or Brownian pattern.
resulted in creating clusters with small-scale crowding, along with
larger-scale dispersion. In this pattern mussels maximized
number of mussels immediately close to them (which reduced their chance
of being dislodged by wave action) while at the same time minimized the
number of mussels in the general area (which would increase
competition for food). [de
Jager, Monique, Franz J. Weissing, Peter M. J. Herman, Bart A. Nolet,
and Johan van de Koppel, 2011.
LÚvy Walks Evolve Through Interaction Between Movement and
Environmental Complexity. Science 332 pp
commentary on the article is on page 1514 of the same issue]
et al., (1980)
Emily, Gretchen M. Moeser, Sean B. Thompson, Laura C. Coutts, and
A. Craig, 2008. Mussel attachment on rocky
effect of flow on byssus production. Integrative and
Biology 48:6 pp 801-807
Gosling, Elizabeth, 1992. The Mussel Mytilus:
Physiology, Genetics and Culture. Developments in Aquaculture
Fisheries Science 25. Elsevier. 563 pp.
Paola C., Henry S. Carson, Geoffrey S.
Cook, F. Joel
Fodrie, Bonnie J. Becker, Claudio
DiBacco, and Lisa A.
Levin, 2012. What controls connectivity?
multi-species approach. Integrative and Comparative Biology
Wootton, J. Timothy, 2002. Mechanisms of
consumers and the rise and fall of species dominance.
Research 17 pp. 249-260
Zweibel, Jennifer A. and Markes E. Johnson, 1995.
mytilid and petricolid bivalves from the open rocky shores of Pacific
California (Mexico): Unusual preservation of
Journal of Coastal Research 11:3 pp 704-716
General Notes and
Observations: Locations, abundances,
unusual behaviors, etc.:
Fossils of this species were found in a very-well preserved layer
with the Pleistocene-Cretaceous nonconformity at Punta Cabras on the
coast of Baja california (Zweibel
and Johnson, 1995)
M. californianus often dominates the lower
intertidal zone on
the open coast. The seastar Pisaster
ochraceous is an important predator.
Photo by Dave Cowles near Goodman Creek, 7-2004
A cluster of M. californianus on rocks at Little
Mar, Ca. Note how they cover much of large areas of the lower
Photo by Dave Cowles, March 2005.
In areas exposed to very heavy surf, mussels may be most common in
cracks or depressions where they have not been swept off by logs
In other spots, they may be abundant
on exposed rock faces but the aggregations often have an abrupt lower
edge, probably due to predation by Pisaster
ochraceous (below). Photos by Dave
Cowles, Sept 2005 at Shi
California mussels and the goosneck barnacle Mitella
polymerus often compete for space in exposed areas
of the lower
intertidal. Mytilus usually eventually
wins unless it is removed
Photo by Dave Cowles, September 2005 at Shi shi beach, WA
This species can grow very large. Photo by Dave Cowles,
Corona del Mar, CA March 2005
Individuals hold onto the substrate or to one another by byssal
which they secrete by a gland on their foot. Photo by Dave
mussels cluster so tightly together they often attach to one another,
making a several-mussel-thick pile of animals called a druse. Parts of
the druse can then be torn off by waves and cast ashore. Photo at
Kalaloch Beach #4 by Dave Cowles, July 2022
On mussels such as Mytilus californianus, only the posterior
adductor scar is large. In this photo anterior is
to the left
and posterior is to the right.
line is marked by the border between the whitish and dark nacre.
The oval-shaped, shiny scar near the pallial
line on the right is the scar
for the posterior
Mussel recruitment looked very good at Kalaloch in 2008. This
view shows an intertidal rock surface with many small mussels (about
cm long, probably first-year individuals) with many more smaller brown
individuals (less than 1 cm long, probably newer recruits) packed
among them. Such surfaces were common in summer
by Dave Cowles, July 2008
Authors and Editors of Page:
Dave Cowles (2002): Created original page
Edited by Hans Helmstetler 12-2002, Dave Cowles 2005