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Animal profile

Ochre Sea Star

Pisaster ochraceus

AsteroideaWave-exposed rocky intertidal shores of the north-east Pacific

Field profile

A stout five-armed sea star, orange or purple, common on surf-swept rocks. It preys mainly on the California mussel. Experimental work on this species produced one of ecology's foundational concepts.

Scope note

This is an editorial profile, not a diagnostic field-identification guide or a substitute for current conservation assessments. Follow the cited sources on each fact for the evidence trail.

Published field notes

2025-12-11

Ochre Sea Star

The ochre sea star gave ecology the keystone idea

Removing this one predator from experimental patches of Washington shoreline caused the community to collapse from roughly fifteen species to a near-monoculture of mussels. The result introduced the term keystone species in 1969.

Read with evidence →

Ochre Sea Star | Daily Animal Facts