Ochre Sea Star (Pisaster ochraceus)

Other Names: Purple star, common sea star, Pacific sea star

Description: Ochre stars are a beautiful species of sea star that come in a wide array of colors from deep purple to maroon to red and to various shades of orange. Ochre sea stars generally have 5 arms and can reach sizes of 36 centimeters (14 inches) in width. This intriguing creature is an echinoderm, which translates to “spiny skin.” Like other echinoderms, it has little white bumps on the topside of its body called ossicles. These ossicles are part of a sea star’s endoskeleton and they provide rigidity and protection. On the underside of a sea star, one will find tons of little tube feet that sea stars use to move, grab prey, and cling onto rocks. The mouth is also located on the underside of this sea star.

Habitat: Ochre sea stars live in the intertidal zone, ranging geographically from Alaska to California. Ochre sea stars prefer clinging onto rocks, often underneath mussel beds. To find one, it’s best to get down low and look within rock crevices and underneath rocky overhangs. They sometimes like to cling onto each other in dense groups.

Diet: Ochre sea stars love eating mollusks, especially mussels. To do so, they only have to pry open a mussel shell a tiny bit in order to slip in a bag-like structure called the cardiac stomach. This is one of two stomachs a sea star has, and the cardiac stomach is able to digest food outside of the body. Once it's done, the stomach slips back into the sea star’s mouth.

Tide Pool Tidbits:

• Ochre sea stars are the longest-living species of sea star in the Pacific Northwest, reaching ages of up to 20 years old.

• Ochre sea stars used to be found in incredible abundance in the Pacific Northwest of North America, until they were hit by Sea Star Wasting Syndrome in 2013. This disease is believed to be caused by a pathogen, likely a bacterial infection, and could be driven by warming ocean temperatures. When infected, a sea star will suffer from lesions on their body and will lose limbs, ultimately resulting in death. Sea star wasting could be passed through direct contact, which is why we urge people not to touch sea stars. In the past several years we have fortunately seen increases in ochre sea star populations at Haystack Rock, and fewer cases of wasting. 

• Sea stars are a keystone species, which means that their presence keeps certain populations under control within their habitat. In the intertidal zone, sea stars are essential for controlling California mussel populations. Without sea stars present, mussel beds would completely overtake the rocks. Having sea stars around means that many mussels get eaten, which frees up space on the rocks for other marine organisms to live (anemones, other mollusks, etc.). 

• Although sea stars are such voracious mussel predators, they cannot eat all of the mussels on the rocks. Sea star movement is limited by the height of the tides, since they are frozen in place when out of the water. When tides are low, it is easy to see a distinct line between where the sea stars can and cannot reach mussels; the bottom halves of rocks are completely clear except for sea stars and other creatures, and the top halves are entirely crowded by mussels.

Reference: Central Coast Biodiversity