species of seastar
has a radius of up to about 25 cm with stout rays
that taper towards the end. There are usually five rays,
but occasionally as few as 4 or rarely as many as 7. The
from pale orange to dark brown or deep purple (photo).
many small spines (ossicles)
that are arranged in a netlike or pentagonal pattern on the central
Pisaster ochraceus (Brandt,
Common Names: Ochre sea star,
|Individual found at Swirl Rocks, WA in the
Top view, approximately 40 cm in diameter.
|Photo by: Melissa
McFadden, June 2002.
How to Distinguish
Similar Species: Troschel’s
Sea Star (Evasterias
troschelii) may be confused with
troschelii is distinguished from
by the smaller
size and longer,
often thickest a short distance out from the base rather than at the
as in P. ochraceus; clusters of pedicellariae
among the spines that border the ambulacral
grooves, and the absence of a stellate pattern of spines on
surface of the disk.
There are two other, mostly subtidal, local species of Pisaster
but they have different aboral
spines and coloration which allows one to distinguish between the
Range: P. ochraceus
occurs from Prince William Sound in Alaska to Point Sal in Santa
in the low and middle intertidal zones, and sometimes in the subtidal
(to 88 m).
organism occurs on wave-washed
rocky shores. The juveniles are often found in crevices and
History: This species
of seastar is often considered a keystone species in many intertidal
P. ochraceus feeds mainly on mussels
californianus and Mytilus
trossulus) or will also feed on barnacles, snails,
chitons when mussels are absent. P. ochraceus will
insert its stomach
into snail shells or slits as narrow as 0.1 mm between the shells of
Numerous species of mollusks have avoidance responses to the Ochre Sea
Star, often involving moving away. Adult ochre seastars have
predators, but may be eaten by sea otters and sea gulls. P.
more tolerant to air exposure than others in the
and regularly withstands up to 8 hours exposure during low
It is apparently unharmed by up to 50 hours of exposure in laboratory
but they have an inability to tolerate high water temperatures and low
oxygen levels, keeping them out of shallow bays and high tidepools (See
Pincebourde et al., 2008). Sexual reproduction occurs in the
spring or in the early summer. When ready to reproduce,
may account for up to 40 percent of the animal's weight.
occurs in the Puget Sound around May to July. Fertilization
in the sea and development results in free-swimming, plankton-feeding
Embryonic development and larval feeding have been studied in detail,
little is known of juvenile life following settlement and
ochraceus has been the focus of many major studies including
on their digestive gland tissue (which is similar to cells in the
pancreas and secretes materials similar to insulin).
Pisaster ochraceous is less water
than some other intertidal
species such as Pycnopodia
It makes extensive use of water intake through its madreporite
to maintain internal fluid balance (Ferguson, 1994). The
is still highly susceptible to osmotic changes, however. Held
and Harley (2009)
studied populations from high and low
Individuals from both populations were almost complete
osmoconformers over the range of 15 to 30 psu. In both
populations activity (as measured by the righting response) was lowest
at the lowest salinity (15 psu), and the population which had been
living at lower salinity did not have any better righting response than
did the one living at high salinity. The population living at
high salinity, however, did experience a higher mortality after
exposure to 15 psu than did the other population. Feeding
on mussels also varied with salinity, but the maximum feeding rate in
the population living at low salinity was at a lower salinity than that
of the population which lived at a higher salinity.
Seastar wasting disease is caused by the "Seastar associated
densovirus" (SSaDV). During the seastar wasting disease that swept the
US west coast in 2013-2015, a large proportion of the Pisaster
ochraceus found along the coast died. In Oregon, the dieoff was most
prominent in summer 2014 and 2015 but mortality persisted at low levels
through the winter. Wasting was most higher in tidepools than on
exposed rock surfaces. The major die-off was followed by an unusual
increase (up to 300x) in recruitment by young seastars (Menge et al.,
2016). In Burrard Inlet, BC, Canada, the relative abundance of this
species declined in the intertidal while that of Evasterias troschelii
increased after seastar wasting disease appeared in the area. It
appears that both species are susceptible to wasting disease but E. troschelii is less susceptible (Kay et al., 2019)
Return to Main Page
Abbott, and Haderlie, 1992.
Ferguson, John C., 1994. Madreporite inflow of
seawater to maintain
body fluids in five species of starfish. pp. 285-289 in
David, Alain Guille, Jean-Pierre Feral, and Michel Roux
through time. Balkema, Rotterdam.
Mirjam B.E. and Christopher D.G. Harley, 2009.
Responses to low salinity by the sea star Pisaster ochraceus
from high- and low-salinity populations. Invertebrate Biology
Kay, S.W.C., A.M. Gehman, and C.D.G. Harley, 2019. Reciprocal abundance shifts of the intertidal sea stars, Evasterias troschelii and Pisaster ochraceus,
following sea star wasting disease. Proceedings of the Royal Society Part B: Biological Sciences 286:1901 p doi:
Menge, B.A., E.B. Cerny-Chipman, A. Johnson, J. Sullivan, S. Gravem, and F. Chan, 2016. Sea star wasting disease in the keystone predator Pisaster ochraceus
in Oregon: insights into differential populations impacts, recovery,
predation rate, and temperature effects from long-term research. PLoS
One 11:5, May 4, 2016. doi: 10.1371/journal.pone.0153994 (Table 1 and
the conclusion that orange seastars were more susceptible to wasting in
the article was subject to a later correction in PLoS One, 2016, doi: 10.1371/journal.pone.0157302)
C.M., J.L. Burnaford, R.F. Ambrose, L. Antrim, H. Bohlmann, C.A.
Blanchette, J.M. Engle, S.C. Fradkin, R. Gaddam, C.D.G. harley, B.G.
Miner, S.N. Murray, J.R. Smith, S.G. Whitaker, and P.T. Raimondi, 2018.
Large-scale impacts of sea star wasting disease (SSWD) on intertidal
sea stars and implications for recovery. PLoS One 13:3 doi:
Viren, 2006. Responses to salinity of color
polymorphs in two
populations of the seastar Pisaster ochraceus.
Loma Linda University Department of Earth and Biological Sciences.
Sylvain, Eric Sanford, and Brian Helmuth, 2008.
during low tide alters the feeding performance of a top intertidal
Limnology and Oceanography 53(4): 1562-1573
General Notes and
Observations: Locations, abundances,
unusual behaviors, etc.:
Pisaster ochraceus is a major predator of the
californianus in the intertidal zone.
Photo by Dave Cowles,
Goodman Creek, WA, July 2002
The seastars have surrounded this patch of Mytilus californianus
on this nearly horizontal rock surface at Beach #4 and appear to be
cleaning the rock entirely of mussels from the edges inward.
Photo by Dave Cowles, July 2012
This individual is eating a mussel. Photo by Dave Cowles,
The images above and below show some of the variations
pattern of ossicles
on the aboral
Photos by Dave Cowles at Dana Point, CA March 2005
This is the underside (oral
side) of the individual above, showing the ossicles,
The stomach is not everted.
Photo by Dave Cowles of an intertidal specimen from Sares Head, July
2006: Viren Perumal is studying metabolism of
phases of Pisaster ochraceus as a function of
salinity for his MS
research. We have noted that a number of the seastars brought
the lab during late June and July have shed gametes. They
seem to shed in the evening or at night. Click here
to see a movie of Pisaster ochraceous shedding eggs,
to see one shedding sperm.
This closeup of the aboral
surface shows the extended papulae
or coelomic pouches, used for respiration and waste excretion, which
often extended when seastars such as P. ochraceus
seastar's surface a soft, fuzzy apperance.
Photo July 2007 by Kirt Onthank.
This individual on the north side of a large, fairly isolated rock
at Shi Shi beach is dying (see how the central disk and inner ray
are white and sloughing off and one ray has fallen entirely
I could find no mussels and hardly any large barnacles on this rock so
perhaps the seastar has starved to death. Seastars on other,
rocks which had mussels were in good condition. Photo by Dave
|These images, taken of live
encountered at Beach #4 in the positions in which they were found, show
different stages of regeneration.
Normally few individuals in a population are found
regenerating so I
do not know what phenomenon had damaged all these seastars within a
relatively small area. Perhaps sea otters have moved into the
area. Photos by Dave Cowles, July 2012. Later note: This was
just before wasting disease broke out in force, so this may have been
early signs of the disease.
2021 we found few if any of the seastars at Rialto Beach with
wasting disease, but did find this little feller--new growth! Photo by
Dave Cowles, July 2021
This seastar is enjoying a leisurely breakfast of mussels at Kalaloch Beach #4. Photo by Dave Cowles, July 2019
Authors and Editors of Page:
Melissa McFadden (2002): Created original page
Edited by Hans Helmstetler 12-2002; Dave Cowles 2005, 2008