Pisaster ochraceus

Geographic Range

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.

• Biogeographic Regions
• pacific ocean pacific ocean

Habitat

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.

• Habitat Regions
• temperate temperate
• saltwater or marine saltwater or marine

• Aquatic Biomes
• coastal coastal

• Other Habitat Features
• intertidal or littoral intertidal or littoral

Physical Description

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.

• Other Physical Features
• ectothermic ectothermic
• heterothermic heterothermic
• radial symmetry radial symmetry

Development

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.

• Development - Life Cycle
• metamorphosis metamorphosis

Reproduction

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.

• Key Reproductive Features
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• fertilization fertilization
  • external external
• broadcast (group) spawning

There is no parental investment beyond spawning.

• Parental Investment
• pre-fertilization
  • provisioning

Lifespan/Longevity

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.

Behavior

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.

• Key Behaviors
• motile motile

Communication and Perception

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.

• Communication Channels
• chemical chemical

• Perception Channels
• visual visual
• tactile tactile
• chemical chemical

Food Habits

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.

• Primary Diet
• carnivore carnivore
  • eats non-insect arthropods
  • molluscivore molluscivore
  • eats other marine invertebrates
• planktivore planktivore

• Animal Foods
• mollusks
• aquatic crustaceans
• echinoderms
• other marine invertebrates
• zooplankton zooplankton

• Plant Foods
• phytoplankton phytoplankton

• Foraging Behavior
• filter-feeding filter-feeding

Predation

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.

Ecosystem Roles

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.

• Ecosystem Impact
• keystone species keystone species

Economic Importance for Humans: Positive

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

• Positive Impacts
• research and education

Conservation Status

Other Comments

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 .

Additional Links

Encyclopedia of Life

Contributors

Renee Sherman Mulcrone (editor).

Yesenia Ramirez (author), Southwestern University, Stephanie Fabritius (editor), Southwestern University.

References

Banister, K., A. Campbell. 1985. The Encyclopedia of Aquatic Life . New York: Facts of File Publications.

Buchsbaum, R., M. Buchsbaum, J. Pearse, V. Pearse. 1987. Animals Without Backbones 3rd Edition . Chicago & London: The University of Chicago Press.

Grzimeck, B. 1972. Grzimeck's Animal Life Encyclopedia Volume 3 Mollusks and Echnoderms . New York, Cincinnati, Chicago: Van Nostrand Reinhold Company.

McFadden, M. 2002. "Pisaster ochraceus (Brandt, 1835)" (On-line). Accessed December 26, 2004 at http://homepages.wwc.edu/staff/cowlda/KeyToSpecies/Echinodermata/Class%20Asteroidea/Pisaster_ochraceus.html .

Meinkoth, N. 1981. The Audubon Society Field Guide to North American Seashore Creatures . New York: Chanticleer Press, INC.

Multi-Agency Rocky Intertidal Network, 2004. "Pisaster ochraceus (Brandt, 1835): Ochre sea star" (On-line). Multi-Agency Rocky Intertidal Network. Accessed December 26, 2004 at http://www.marine.gov/pisaster.htm .

Nicol, J. 1960. The Biology of Marine Animals . New York: Interscience Publishers, INC.

Paine, R., S. Levin. 1981. Intertidal landscapes: disturbance and the dynamics of pattern. Ecological monographs , 51: 145-178.

Ricketts, E., J. Calvin, J. Hedgpeth. 1985. Between Pacific tides . Stanford, California: Stanford University Press.