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Asterina gibbosa

By Estella King

Geographic Range

The cushion star inhabits the regions of Europe's rocky coasts, most commonly the seas to the south and west of the British Isles. (Nichols and Cooke, 1971)

Habitat

The cushion star commonly occupies shallow rock pools underneath stones, boulders, and overhangs that provide shelter. Other preferred sites include nestling among algae, sponge masses, or on cliff faces. The cushion star is vertically distributed between the depths of sea level and the intertidal to 130 meters, yet littoral cushion stars are only found in rock pools and relatively damp habitats. This vertical distribution may be extended on shores with rock pools, but this extension will not go beyond the high-water-neap-tide level due to an intolerance to dessication at high temperature, inadequate food supply, and complex behavioral responses to gravity and light. Comparative studies on the ecology of the cushion star at Lough Line showed that A. gibbosa are found in the rocky shallow sub-littoral in varying abundance, yet it was absent from any of the outer shore sites. (Emson and Crump, 1984; Grzmek, 1972; Murphy and Jones, 1987; Nichols and Cooke, 1971)

  • Aquatic Biomes
  • temporary pools
  • coastal
  • Range depth
    130 (high) m
    426.51 (high) ft

Physical Description

Asterina gibbosa is a pentagonal shape with five short arms and a diameter up to 6 cm. The tiny, blunt-armed cushion star ranges in color from greenish-gray, yellowish-green, to reddish-brown. The asteroids are considered a slow moving species with the cushion star being the slowest among all, moving approximately 2.5 cm per minute. The cushion star resembles its given name since the body appears to be inflated like a pillow cushion, emphasizing it small size and blunt arms. The class that the cushion star belongs to, Crinoidea, has retained an upwardly-directed mouth. The cushion star has a body consisting of a tiny central disk to carry the main organs. The mouth of the cushion star is located in the center of the underside. Located on the underside of each arm are grooves that lead to the center that contain hundreds of tube-feet. (Grzmek, 1972; Nichols and Cooke, 1971)

Development

Eggs are usually laid on the underside of stones by female Asterina gibbosa. Up to three weeks later, the young hatch bipinnaria and later into brachiolaria larvae. The larvae are bilaterally symmetrical and metamorphose into juveniles. (Dale, 2000; Marlin, 11/24/04)

Reproduction

The cushion star is one of the few sequential hermaphroditic echinoderms. Younger and smaller individuals are males, developing into females as they increase in size and age. Male and female gametes are not readily distinguishable to the naked eye. One would have to see the gonads or see them actually spawning. The gonads on the cushion star are located in each arm. These gonads release the gametes through gonaducts that are located on the central body between the arms. The male gametes are produced first and later only female gametes are produced. Female A. gibbosa deposit up to 1000 eggs in a specific location (usually underside stones) to the ground in the process of reproduction. At the beginning of reproduction, many starfish belonging to the asteroid species form aggregations. In Asterina gibbosa, several males surround or congregate around one female during reproduction. (Grzmek, 1972; Nichols and Cooke, 1971; Skewes, 11/10/2002)

  • Range number of offspring
    1000 (high)

There is no post-spawning parental investment.

  • Parental Investment
  • pre-fertilization
    • provisioning

Lifespan/Longevity

Cushion stars can live up to seven years. (Barrett, 1997)

  • Typical lifespan
    Status: wild
    7 (high) years

Behavior

The cushion star is mobile, but not quick. Since it has a speed of only 2.5 cm per minute, this starfish is the slowest of its class. This lack of speed and agility is due to the length of its rays and the thickness of its body. Asterina gibbosa is extremely sensitive to light and temperature, resulting in its preference to sheltered areas of habitation. Studies conducted to observe factors affecting the respiraion of intertidal A. gibbosa showed that the aquatic and aerial oxygen uptake by this species was low when compared with other intertidal invertebrates. The studies also concluded that small cushion stars were less temperature-dependent than larger cushion stars, regarding aquatic oxygen uptake. (Grzmek, 1972; Murphy and Jones, 1987)

Communication and Perception

In general, echinoderms have nerve nets and non-centralized nervous systems. Asteroids have optic cushions, or eyespots, and respond to light. Echinoderms in general respond to chemicals, light and touch. (Brusca and Brusca, 2003)

Food Habits

Cushion stars are omnivorous. As with other starfish A. gibbosa feed themselves by inverting their stomachs in order to digest the food they eat. Their diet includes molluscs, worms and ophiuroids that are also found among rocky shores. They also eat microorganisms, decaying seaweeds and dead invertebrates. (Marlin, 11/24/04; Nichols and Cooke, 1971)

  • Animal Foods
  • carrion
  • mollusks
  • aquatic or marine worms
  • echinoderms
  • other marine invertebrates

Predation

Starfish are most vulnerable in their larval stage. Few young survive to adulthood.

Economic Importance for Humans: Positive

The cushion star does not have any positive effects on humans.

Economic Importance for Humans: Negative

The cushion star does not have any adverse effects on humans.

Conservation Status

The species is not threatened, but an oil spill at the entrance to Milford Haven in February 1996 spread of 70,000 tons of oil along the Pembrokeshire coast. This location had a major population of Asterina gibbosa which was greatly affected because of the spill. However, observations were made eight weeks after the incident, and there was a good survival of the larger Asterina gibbosa, even some living near small pockets of oil underneath rocks. (Crump and Emson, 1996)

Contributors

Renee Sherman Mulcrone (editor).

Estella King (author), Southwestern University, Stephanie Fabritius (editor), Southwestern University.

Glossary

Atlantic Ocean

the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.

World Map

carnivore

an animal that mainly eats meat

carrion

flesh of dead animals.

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

detritivore

an animal that mainly eats decomposed plants and/or animals

detritus

particles of organic material from dead and decomposing organisms. Detritus is the result of the activity of decomposers (organisms that decompose organic material).

ectothermic

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

fertilization

union of egg and spermatozoan

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.

macroalgae

seaweed. Algae that are large and photosynthetic.

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

native range

the area in which the animal is naturally found, the region in which it is endemic.

omnivore

an animal that mainly eats all kinds of things, including plants and animals

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

pheromones

chemicals released into air or water that are detected by and responded to by other animals of the same species

protandrous

condition of hermaphroditic animals (and plants) in which the male organs and their products appear before the female organs and their products

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

References

Barrett, R. 1997. "Echinodermata: Cushion Stars" (On-line). Excerpted from The Oxford Interactive Encyclopedia. Accessed December 14, 2004 at http://ourworld.compuserve.com/homepages/BMLSS/cushion.htm.

Brusca, R., G. Brusca. 2003. Invertebrates. Sunderland, Massachusetts: Sinauer Associates, Inc..

Crump, R., R. Emson. 1996. "Oral Contribution: Observations on the Effects of the" (On-line). Accessed February 16, 2001 NO LINK at http://www.calacademy.org/research/izg/echinoderm/conference/.

Dale, J. 2000. "Starfish Reproduction" (On-line). Starfish science. Accessed December 14, 2004 at http://www.vsf.cape.com/~jdale/science/reproduction.htm.

Emson, R., R. Crump. 1984. Comparitive Studies on the Ecology of *Asterina Gibbosa* and *A. Phylactica* at Lough Line. Journal of the Marine Biological Association of the United Kingdom, 64: 35-53.

Grzmek, B. 1972. Grzmik's Animal Life Encyclopedia. New York: Van Nostrand Reinhold Company.

Marlin, 11/24/04. "Cushion Star, Asterina gibbosa" (On-line). Marlin, the marine life information network for Britain and Ireland. Accessed December 14, 2004 at http://www.marlin.ac.uk/learningzone/species/LZ_Astgib.htm.

Murphy, C., M. Jones. 1987. Some Factors Affecting the Respiration of Intertidal *Asterina Gibbosa*. Journal of the Marine Biological Association of the United Kingdom, 67: 717-727.

Nichols, D., J. Cooke. 1971. The Oxford Book of Invertebrates. Oxford: Oxford University Press.

Picton, B. E., 2002. "A Field Guide to the Shallow-Water Echinoderms of the British Isles" (On-line). Asterina gibbosa. Accessed December 14, 2004 at http://www.habitas.org.uk/marinelife/species.asp?item=ZB1130.

Skewes, M. 11/10/2002. "Asterina gibbosa. A cushion star" (On-line). Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme. Accessed December 14, 2004 at http://www.marlin.ac.uk/species/Asterinagibbosa.htm.

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