The Purple Sea Star, formally known as Pisaster ochraceus, is one of the most recognizable sea star species along the North American Pacific Coast. It is often called the Ochre Sea Star due to its common color variations, though its purple form gives it the popular common name. Understanding where this animal lives requires looking at its extensive geographic range and preferred micro-environments.
Defining the Geographic Range
The distribution of Pisaster ochraceus is remarkably broad, spanning the entire temperate Pacific coastline of North America. Its range begins far north, extending from the Prince William Sound in Alaska, continuing along the Aleutian Islands, and traveling south.
The sea star is a common sight along the coasts of British Columbia, Washington, Oregon, and California. Their southern limit extends down into Mexico, reaching as far as Isla Cedros in Baja California. While the overall distribution is continuous, the sea star is particularly common in the northern parts of its range due to its preference for cooler conditions. Within this vast territory, the highest concentrations are found in areas known for significant upwelling and rich nutrient availability.
Specific Habitat Requirements
Within its expansive geographic range, the purple sea star is almost exclusively found in rocky environments. It inhabits the intertidal zone, the strip of coastline exposed to air at low tide and submerged at high tide.
The sea star requires a hard substrate, such as bedrock or large boulders, to attach its hundreds of tube feet. These tube feet allow it to remain anchored against powerful ocean forces and cling tightly to the rock, even in areas with heavy wave action. Preferring exposed, wave-washed rocky shores, the species is commonly found in areas rich with its primary prey, the California mussel (Mytilus californianus). While most commonly observed in the low to mid-intertidal zone, the sea star can also be found in the subtidal zone, sometimes as deep as 90 meters (300 feet).
Color Variations and Identification
Despite the popular name, the Purple Sea Star, or Ochre Sea Star, displays a remarkable color polymorphism. While deep purple individuals are abundant and striking, the species can also be found in shades of bright orange, reddish-brown, yellow, and dull brown. The color variation is a natural characteristic of the species and is not tied to gender or specific location, although certain regions show a higher proportion of one color over another.
For example, populations in the protected waters of the Puget Sound and Strait of Georgia are often almost entirely brilliant purple. In contrast, populations along the open Pacific coast of California and Oregon show a greater mix of orange and brown individuals. The coloration is thought to be related to the accumulation of carotenoid pigments, such as mytiloxanthin, which the sea star sequesters primarily through its diet.
Identifying Pisaster ochraceus is also possible by its size and structure, regardless of its color. This sea star typically has five thick, stout arms radiating from a central disk, and can grow quite large, reaching up to 45 centimeters (18 inches) in diameter. The upper surface of the animal is covered in a pattern of small, white spines, which helps distinguish it from other similar sea star species.