Ochre starfish, scientifically known as Pisaster ochraceus, are a prominent and ecologically significant species found along the North American Pacific coast. These marine invertebrates are easily recognized by their five stout arms, typically measuring 10 to 25 centimeters across, and their varied coloration, which can include shades of purple, orange, yellow, reddish, or brown. They are considered a keystone species, meaning their presence plays an important role in maintaining the balance and diversity of their ecosystems.
Pacific Coast Range
Ochre starfish are broadly distributed along the rocky intertidal shores of the Pacific Coast of North America. Their extensive geographical range stretches from Prince William Sound in Alaska, southwards along the coast, and extends all the way to Baja California, Mexico. They are a common sight within this vast area, particularly abundant in the cooler waters of the Pacific Northwest.
Intertidal Zone Dwellers
Within their broad Pacific Coast range, ochre starfish exhibit a strong preference for rocky intertidal zones. These areas, characterized by their exposure to both air and water due to tidal cycles, include tide pools and exposed shorelines. They commonly inhabit the middle to lower portions of the intertidal zone, where they can cling firmly to rocks using thousands of tiny tube feet equipped with suckers. While primarily intertidal, they can also be found in shallow subtidal areas, venturing to depths of up to 90 meters (300 feet). Younger starfish often seek refuge in crevices and beneath rocks.
Conditions for Survival
The distribution of ochre starfish is shaped by several environmental factors to which they are highly adapted. They thrive in areas with significant wave action, possessing strong tube feet that enable them to resist being dislodged from rocky surfaces. Their body shape can also adapt to varying wave exposures, with individuals in more exposed areas often developing slender arms to reduce dislodgement risk.
Ochre starfish demonstrate a tolerance for temperature fluctuations experienced during tidal exposure, and they often seek shaded areas to avoid thermal stress. They can endure periods out of water for up to eight hours and tolerate a 30% loss of body fluids. While generally resilient, they show some susceptibility to extreme osmotic changes, though populations can acclimatize to lower salinity conditions.
A suitable rocky substrate is crucial for their attachment and movement, as well as for the availability of their primary food sources. Their diet mainly consists of mussels, especially California mussels, along with barnacles, limpets, snails, and small crustaceans, making the presence of these prey animals a significant factor in their habitat selection.