Pisaster ochraceus

Pisaster ochraceous can be found anywhere from Alaska to Baja California. It is most commonly found in the Northeastern Pacific, being that it is a cold-water species. However, it is common in bays all year. (Banister and Campbell, 1985; Meinkoth, 1981; Multi-Agency Rocky Intertidal Network, 2004)

Pisaster ochraceous can be found on wave-washed rocky shores, from above the low-tide zone to 90 m in depth. Because they can live in shallow water they need to survive in these living conditions, including strong surges, big temperature changes, dilution by rainfall, and dessication. Pisaster ochraceous is very resistant to dessication and it can tolerate a loss of thirty-percent of its body weight in body fluids. (Grzimeck, 1972; Meinkoth, 1981)

The radius of P. ochraceus is anywhere from about 10 to 18 inches (25 to 45 cm) in diameter. Yellow, orange, brown, reddish or even purple make up the ranging colors of this heavy starfish. Basically it has a good size middle disk with five stout arms sticking out. On its upper side it has short, white spines in the pentagonal pattern. (McFadden, 2002; Meinkoth, 1981)

Pisaster ochraceous develops through several larval stages, one including the brachiolaria larva. Using ciliated arms to sweep food into its mouth, it glides through the water column. The cilia drive locomotion of the larva is supplemented by these same arms. The larva attaches itself to the substratum as it settles because each arm has a glandular tip. The five-armed adult is formed because it undergoes metamorphosis. Adults continue growing and the rate of growth is dependent on its food supply. (Banister and Campbell, 1985; Grzimeck, 1972; Nicol, 1960; Ricketts, et al., 1985)

Pisaster ochraceous is mainly dioecious. The male gametes develop, but later only females ones are produced. During a transitional period, both eggs and sperm are produced. A pair of gonads branches into each arm off a circular genital strand located along the oral inner surface of the disc. Each gonad looks like a feathery cluster of tubules. During maturation of the gametes, the gonads greatly increase in size, pushing into the perivisceral cavity of the arms, often right up to the ends of the arms. The gonopores of the individual gonads open at the bases of the arms. (Grzimeck, 1972)

There is no parental investment beyond spawning.

From studies in oceans and aquariums, it seems that many asteroids achieve a minimal life span of four to six years, and Pisaster ochraceous could reach an age of twenty years. (Grzimeck, 1972; Multi-Agency Rocky Intertidal Network, 2004)

The nervous system is simple and there is no brain, or even ganglia that might coordinate activities. A nerve ring encircles the mouth and connects with five radial nerves, which extend the length of the arms, below the radial canals of the water vascular system. The nerve ring relays impulses between the radial nerves so that one arm can lead and the others follow. (Buchsbaum, et al., 1987)

The neurosensory cells scattered over the asteroid body respond to mechanical, chemical, and optical stimuli. Sensory organs are developed only at the base of each terminal tentacle. At this location a great number of light-sensitive cells form an optic cushion which contains several ocelli. (Buchsbaum, et al., 1987; Grzimeck, 1972)

At the larval stage, Pisaster ochraceus are filter feeders, eating plankton.

Like all sea stars, an adult P. ochraceous has tube feet which they use for locomotion and for handling prey. Pisaster ochraceous feeds on mussels, chitons, and limpets, which they slowly pry open and devour. Snails, barnacles, echinoids, even decapod crustacea are also eaten. Pisaster ochraceous everts its stomach over the prey if it is too large to be swallowed whole, and digests the prey before swallowing it. (Banister and Campbell, 1985; Grzimeck, 1972; Nicol, 1960; Ricketts, et al., 1985)

Sea otters and gulls prey on this starfish. Pisaster ochraceus can retract such sensitive areas as the podia and skin papillae. Additionally, they may be able to shut the ambulacral grooves which contain the tube-feet, and then spread the spines over them protectively. (Grzimeck, 1972)

Pisaster ochraceous is a predator and is a prey to sea otters and sea gulls. Its role as a keystone species has been well studied. In intertidal areas of Washington, when it was removed, the diversity of species in the area decreased. (McFadden, 2002; Paine and Levin, 1981)

The only positive benefit for humans is that they are admired by tourists as they are clinging to the rocks on a bay area.

This is the most common, large intertidal sea star and it occurs in great numbers on mussel beds on exposed coasts. Pisaster ochraceous is more tolerant to air exposure than any other Pisaster. (McFadden, 2002)