Ochre sea star

Ochre sea stars live by the sea in western North America.

When the tide goes out, you can find them holding on to rocks. They can stay out of the water for hours!

Ochre sea stars live along the Pacific coast of North America, from Alaska down to California. They cling to rocky shores where waves crash, in the middle and lower parts of the shore that are covered and uncovered by the tides. Young ones hide in cracks and under rocks.

They are tough. At low tide they can stay out of the water for up to 8 hours, and they can lose almost a third of their body fluids and survive. But they cannot handle very warm water or water low in oxygen, so they avoid shallow bays and high tide pools.

Walla Walla University's guide gives the range as Prince William Sound, Alaska, to Point Sal, Santa Barbara County, California; Animal Diversity Web extends it to Baja California. The map shades the United States and Canada, where both agree; it lives only along their Pacific coasts.

It occurs in the low and middle intertidal and sometimes subtidally, to 88 meters, on wave-washed rocky shores. It regularly withstands 8 hours of air exposure at low tide and survived up to 50 hours in the laboratory, and ADW reports it can tolerate losing 30 percent of its body weight in fluids. Its intolerance of high temperature and low oxygen keeps it out of shallow bays and high tidepools.

Ochre sea stars love to eat mussels.

They pull the mussel's shells open a tiny bit. Then they push their tummy inside and eat the mussel!

The ochre sea star mainly eats mussels. When mussels are scarce, it eats barnacles, snails, limpets and chitons instead.

It has a clever way to eat a closed mussel. It holds the mussel with its many tube feet and slowly pries the shells apart. Then it slides its stomach out of its body and into a gap as narrow as a tenth of a millimeter, about as thin as a hair, and digests the mussel right inside its own shell. Many snails and other molluscs try to move away when an ochre star comes near.

Walla Walla University's guide lists mussels, especially Mytilus californianus and M. trossulus, as the main prey, with barnacles, snails, limpets and chitons when mussels are absent. The sea star can insert its everted stomach into snail shells or slits as narrow as 0.1 millimeter between bivalve shells, and many molluscs show avoidance responses to it.

ADW notes that it handles prey with its tube feet and everts its stomach over prey too large to swallow, digesting it before swallowing. Its larvae are plankton feeders.

Ochre sea stars are very important to their rocky shore.

When scientists took them away from a shore, fewer kinds of plants and animals lived there.

A keystone is the stone at the top of an arch that holds the whole arch together. Scientists call some animals keystone species because they hold their whole community together. The ochre sea star was the animal that gave scientists this idea.

Ochre sea stars eat lots of mussels, and they can change the whole community of living things on a rocky shore. In Washington State, when ochre sea stars were removed from a shore, the number of kinds of living things there went down.

MARINe (the Multi-Agency Rocky Intertidal Network) notes that Pisaster ochraceus was the basis of the keystone species concept because of its potential to dramatically alter the rocky intertidal community. ADW reports that when it was removed from intertidal areas of Washington, species diversity decreased.

Adults have few predators; sea otters and gulls eat them. After wasting disease reduced ochre stars, Walla Walla University's guide reports that in Burrard Inlet, British Columbia, the mottled star Evasterias troschelii, which appears less susceptible, increased in relative abundance.

In 2013, many ochre sea stars got sick and died.

Scientists are studying the sickness to help sea stars. In some places, lots of baby ochre sea stars arrived afterward.

In 2013, sea stars along much of North America's Pacific coast began to die from a sickness called sea star wasting disease. It was first noticed in ochre sea stars in Washington State in June 2013. Sick stars look deflated, then their bodies break down. More than 20 kinds of sea stars were affected, and huge numbers of ochre sea stars died.

There is some hopeful news. In Oregon, many young ochre sea stars settled on the shore after the die-off. In 2025, scientists identified a bacterium that causes the disease in sunflower sea stars, and they are now studying whether it affects ochre stars too.

Ochre sea stars have not been evaluated for the IUCN Red List (GBIF's Red List copy: Not Evaluated). MARINe reports that the current sea star wasting disease outbreak was first noted in ochre stars in June 2013 on the Washington coast; die-offs were most severe in 2013 to 2014 and the disease persists at low levels, with regional flare-ups. Similar die-offs occurred in the 1970s, 1980s and 1990s, but never at this magnitude or scale.

In Oregon the die-off peaked in summers 2014 and 2015 and was followed by recruitment of young sea stars up to 300 times higher than usual (Menge and colleagues, 2016, cited by Walla Walla University). In 2025 Prentice and colleagues identified a strain of Vibrio pectenicida as a causative agent of wasting in sunflower stars; MARINe says more research is needed on its role in other species.