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Pisaster ochraceus

By Yesenia Ramirez

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. (Banister and Campbell, 1985; Meinkoth, 1981; Multi-Agency Rocky Intertidal Network, 2004)

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. (Grzimeck, 1972; Meinkoth, 1981)

  • Range depth
    90 (high) m
    295.28 (high) ft

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. (McFadden, 2002; Meinkoth, 1981)

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. (Banister and Campbell, 1985; Grzimeck, 1972; Nicol, 1960; Ricketts, et al., 1985)

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. (Grzimeck, 1972)

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

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. (Grzimeck, 1972; Multi-Agency Rocky Intertidal Network, 2004)

  • Typical lifespan
    Status: wild
    20 (high) 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. (Buchsbaum, et al., 1987)

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. (Buchsbaum, et al., 1987; Grzimeck, 1972)

Food Habits

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

Like all sea stars, an adult P. ochraceus 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)

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

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. (Grzimeck, 1972)

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. (McFadden, 2002; Paine and Levin, 1981)

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. (McFadden, 2002)

Contributors

Renee Sherman Mulcrone (editor).

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

Glossary

Pacific Ocean

body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.

World Map

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

external fertilization

fertilization takes place outside the female's body

fertilization

union of egg and spermatozoan

filter-feeding

a method of feeding where small food particles are filtered from the surrounding water by various mechanisms. Used mainly by aquatic invertebrates, especially plankton, but also by baleen whales.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

intertidal or littoral

the area of shoreline influenced mainly by the tides, between the highest and lowest reaches of the tide. An aquatic habitat.

keystone species

a species whose presence or absence strongly affects populations of other species in that area such that the extirpation of the keystone species in an area will result in the ultimate extirpation of many more species in that area (Example: sea otter).

metamorphosis

A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.

molluscivore

eats mollusks, members of Phylum Mollusca

motile

having the capacity to move from one place to another.

phytoplankton

photosynthetic or plant constituent of plankton; mainly unicellular algae. (Compare to zooplankton.)

planktivore

an animal that mainly eats plankton

radial symmetry

a form of body symmetry in which the parts of an animal are arranged concentrically around a central oral/aboral axis and more than one imaginary plane through this axis results in halves that are mirror-images of each other. Examples are cnidarians (Phylum Cnidaria, jellyfish, anemones, and corals).

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

visual

uses sight to communicate

zooplankton

animal constituent of plankton; mainly small crustaceans and fish larvae. (Compare to phytoplankton.)

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.

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