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Ophiothrix fragiliscommon brittlestar

By Patricia Holland

Geographic Range

Common brittle stars are commonly found off the coast of the British Isles (though unrecorded from the east coast of Scotland) as well as on all other coasts bordering the North Sea and throughout the eastern Atlantic Ocean, as far south as the Cape of Good Hope. They are also found around the Azorean Islands. (Aronson, 1989; Jackson, 2008; de Kluijver and Ingalsuo, 2012)

Habitat

Common brittle stars are epifaunal and live in extremely large groups offshore (as many as 2000 individuals recorded) known as brittle star beds. Within the intertidal zone, they are most often found individually. They typically prefer hard substrata (sand and shell bottoms) and are often found under shells or rocks, but can be found on rocky reefs and soft substrata as well. This brittle star is found in shallow waters but also as deep as 350 m, and prefers areas with strong current. Because high levels of sedimentation can prevent them from feeding and eventually halt respiration, this species avoids areas of high sedimentation. ("Common brittlestar (Ophiothrix fragilis)", 2012; Aronson, 1989; Jackson, 2008; de Kluijver and Ingalsuo, 2012)

  • Range depth
    0 to 350 m
    0.00 to 1148.29 ft

Physical Description

Common brittle stars have cryptic coloration, helping them avoid predation. Individuals are usually red, white, or brown and some are also banded or spotted. Their central body discs range from 2-20 mm in diameter and their five legs are very long and slim (typically five times the diameter of the body in length) and are segmented, with tube feet and seven serrated spines per segment. The central body is covered in spines as well. ("Common brittlestar (Ophiothrix fragilis)", 2012; Aronson, 1989; Fish and Fish, 2011; Jackson, 2008; MacBride, 1907; Morgan and Jangoux, 2005; de Kluijver and Ingalsuo, 2012)

  • Sexual Dimorphism
  • sexes alike
  • Range length
    2 to 20 mm
    0.08 to 0.79 in

Development

Common brittle stars have three major life stages: larva, juvenile, and adult. Development from the larval to the adult stage takes 20-30 days, depending on nutrient availability, while development to full maturity may take 6-10 months. (Burton, 1970; Jackson, 2008; MacBride, 1907; Morgan and Jangoux, 2005)

Common brittle star eggs are 0.1 mm in diameter. Approximately 12 hours after fertilization, the oval-shaped larvae leave their egg membranes and form a vacuolated crest (a crest with a fluid-filled cavity in the center). A day later they form posterolateral arms. The beginning of the exotrophic larval period is determined by the formation of the mouth and anus (typically during the third day). During the next 10 days, common brittle stars develop their anterolateral, postoral, and postdorsal pairs of arms. Metamorphosis begins around the 15th day of development, signaled by the split of the hydrocoele (water vascular system) into 5 lobes and subsequent wrapping around the esophagus. Next, brittle stars enter the endotrophic period. Their larval arms (not including the posterolaterals) regress, followed by the regression of the esophagus and intestine. During this time, larvae begin to develop their five adult tentacles as well as mouths and, on the undersides of the arms, tube feet (podia). Finally, juveniles lose their larval posterolateral arms and develop hooks on the ends of their arms which are used to latch on to adults. Juveniles depend on adults to help them feed until they are capable feeding on their own. (Burton, 1970; MacBride, 1907; Morgan and Jangoux, 2005)

Reproduction

Common brittle stars mate by releasing sperm and eggs into the water, with the release of sperm by the males triggering females to release eggs. The eggs are fertilized and develop in the water column. Although Common brittle stars have been reported to breed year-round in some areas, and as late as October in others, gonads are typically most developed from May-July. (Jackson, 2008; Morgan and Jangoux, 2005)

It is believed that individuals reach sexual maturity at approximately 10 mm body disc diameter, though gonad tissue can be found in individuals as small as 3 mm. This species typically breeds during the summer months from May-July, but there is evidence that some of the population may be able to breed throughout the year. Individuals usually spawn once per breeding season. (Barker, 2000; Jackson, 2008; MacBride, 1907; Morgan and Jangoux, 2005)

  • Breeding interval
    Common brittle stars generally spawn once per year
  • Breeding season
    May to July

Adult common brittle stars help juveniles to feed. The juveniles they aid, however, may not be their own: as larvae develop in the water column, strong currents may cause a passive migration, taking them to an entirely different population. (Barker, 2000; Jackson, 2008; MacBride, 1907; Morgan and Jangoux, 2005)

Lifespan/Longevity

This species lives an average of 10 years in the wild. Nothing is known about their lifespan in captivity. (Fish and Fish, 2011)

  • Average lifespan
    Status: wild
    10 years

Behavior

Not much is known about the behavior of common brittle stars. They have been found to form dense aggregations, from 340 to over 2000 individuals per m^2. They exhibit cryptic behavior, hiding under rocks and crevices by day and coming out to feed at night. Studies of larvae indicate that they travel passively in the water column to new locations. (Aronson, 1989; Barker, 2000; Fish and Fish, 2011; MacBride, 1907; Warner, 1971)

Home Range

Territory size varies depending on the population. Researchers have found that there is often an ophiuroid-free "halo" separating the species from nearby rocky reefs where there may be predators. (Aronson, 1989)

Communication and Perception

Not much is known about how these brittle stars communicate. It is known that they form their beds based on interaction with other brittle stars, not due to environmental cues. They is some evidence that they communicate using pheromones (as do other echinoderms), particularly during breeding. (Hughes, 1998)

Food Habits

This brittle star is a nocturnal passive suspension feeder. To feed, it lifts its arms through crevices in rocks, passing particles to its mouth where it uses the two pairs of tube feet in its mouth and both a vertical row of teeth and group of tooth papillae to consume its food. This species' diet is made up largely of detritus, diatoms, and phytoplankton. It will also occasionally scavenge dead material. (Aronson and Blake, 2001; Aronson, 1989; Fish and Fish, 2011; Jackson, 2008; Morgan and Jangoux, 2005)

Predation

Common brittle stars are prey to many species of fish, portunid crabs, and some species of starfish. Their main predators include ballan wrasses, cuckoo wrasses, common dragonets, velvet crabs, spiny starfish and common starfish. Brittle stars have two main defense mechanisms against predators such as these. They have cryptic coloring and behaviors, often feeding at night and hiding during the day, and also have the ability to lose their arms, which later regenerate, to distract predators. (Aronson and Blake, 2001; Aronson, 1989; Colin, 1988; Fontaine, 1968)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

Common brittle stars have several ecological roles. This species is prey for a variety of fish, crabs, and starfish and their large beds can create shelter for other animals such as bivalves. These animals feed upon diatoms and phytoplankton, removing particulates from the water column; they are also detritivores, feeding on decaying material from the ocean floor. Common brittle stars are host to a number of ectoparasitic copepod species, and some studies have found that they have become a host to an orthonectid species as well. (Aronson and Blake, 2001; Aronson, 1989; Colin, 1988; Fish and Fish, 2011; Fontaine, 1968; Jackson, 2008; Morgan and Jangoux, 2005; Stöhr and Hansson, 2012)

Commensal/Parasitic Species
  • Collocheres gracilicauda (Subclass Copepoda, Subphylum Crustacea)
  • Paranthessius anemoniae (Subclass Copepoda, Subphylum Crustacea)
  • Thalestris longimana (Subclass Copepoda, Subphylum Crustacea)
  • Thaumatopsyllus paradoxus (Subclass Copepoda, Subphylum Crustacea)
  • Rhopalura ophiocomae (Family Rhopaluridae, Class Orthonectida)

Economic Importance for Humans: Positive

Common brittle stars have no known economic importance to humans.

Economic Importance for Humans: Negative

Dense aggregations of these brittle stars can be a nuisance to fisherman. (Aronson, 1989)

Conservation Status

Common brittle stars have not been evaluated for the IUCN Redlist. However, due to their general abundance, the species is not considered to be in need of targeted conservation efforts. (IUCN, 2012)

Contributors

Patricia Holland (author), Radford University, Karen Powers (editor), Radford University, Kiersten Newtoff (editor), Radford University, Melissa Whistleman (editor), Radford University, Jeremy Wright (editor), University of Michigan-Ann Arbor.

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

Ethiopian

living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.

World Map

Palearctic

living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

World Map

benthic

Referring to an animal that lives on or near the bottom of a body of water. Also an aquatic biome consisting of the ocean bottom below the pelagic and coastal zones. Bottom habitats in the very deepest oceans (below 9000 m) are sometimes referred to as the abyssal zone. see also oceanic vent.

biodegradation

helps break down and decompose dead plants and/or animals

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.

colonial

used loosely to describe any group of organisms living together or in close proximity to each other - for example nesting shorebirds that live in large colonies. More specifically refers to a group of organisms in which members act as specialized subunits (a continuous, modular society) - as in clonal organisms.

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

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

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.

induced ovulation

ovulation is stimulated by the act of copulation (does not occur spontaneously)

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

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.

motile

having the capacity to move from one place to another.

native range

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

nocturnal

active during the night

oceanic islands

islands that are not part of continental shelf areas, they are not, and have never been, connected to a continental land mass, most typically these are volcanic islands.

pheromones

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

phytoplankton

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

planktivore

an animal that mainly eats plankton

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

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).

reef

structure produced by the calcium carbonate skeletons of coral polyps (Class Anthozoa). Coral reefs are found in warm, shallow oceans with low nutrient availability. They form the basis for rich communities of other invertebrates, plants, fish, and protists. The polyps live only on the reef surface. Because they depend on symbiotic photosynthetic algae, zooxanthellae, they cannot live where light does not penetrate.

saltwater or marine

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

scavenger

an animal that mainly eats dead animals

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

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

solitary

lives alone

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).

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

References

2012. "Common brittlestar (Ophiothrix fragilis)" (On-line). ARKive: Images of Life on Earth. Accessed August 24, 2012 at http://www.arkive.org/common-brittlestar/ophiothrix-fragilis/#text=Biology.

Aronson, R. 1989. Brittlestar beds: Low-predation Anachronisms in the British Isles. Ecology, 70/4: 856-865.

Aronson, R., D. Blake. 2001. Global climate change and the origin of modern benthic communities in Antartica. American Zoologist, 41/1: 27-39.

Barker, M. 2000. Echinoderms 2000. Netherlands: Taylor & Francis.

Burton, R. 1970. The International Wildlife Encyclopedia, Volume 1. United States: Marshall Cavendish.

Colin, P. 1988. Marine Invertebrates and Plants of the Living Reef. Neptune City, NJ: T. F. H. Publications, Inc..

Fish, J., S. Fish. 2011. A Student's Guide to the Seashore. England: Cambridge University Press.

Fontaine, A. 1968. A new Ophiuroid host for {Rhopalura ophiocomae} Giard (Orthonectida:Mesozoa). The Journal of Parisitology, 54/6: 1251-1252.

Hughes, D. 1998. Subtidal brittle star beds: An overview of dynamics and sensitivity characteristics for conservation management of marine SACs. Scottish Association for Marine Sciences, 4: 1-78.

IUCN, 2012. "IUCN Red List of Threatened Species. Version 2012.1" (On-line). Accessed August 25, 2012 at http://www.iucnredlist.org.

Jackson, A. 2008. "Ophiothrix fragilis. Common brittlestar." (On-line). Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme. Accessed August 24, 2012 at http://www.marlin.ac.uk/specieshabitats.php?speciesID=3976.

Jones, N. 1951. The bottom fauna off the south of the Isle of Man. Journal of Animal Ecology, 20/1: 132-144.

MacBride, E. 1907. Some points in the development of Ophiothrix fragilis. Proceedings of the Royal Society of London. Series B, Containing Papers of a Biological Character, 79/534: 440-445.

Morgan, R., M. Jangoux. 2005. Larval morphometrics and influence of adults on settlement in the Gregarious Ophiuroid Ophiothrix fragilis (Echinodermata). Biological Bulletin, 208/2: 92-99.

Stöhr, S., H. Hansson. 2012. "World Register of Marine Species" (On-line). Ophiothrix fragilis. Accessed August 24, 2012 at http://www.marinespecies.org/aphia.php?p=taxdetails&id=125131.

Warner, G. 1971. On the ecology of a dense bed of the brittle-star Ophiothrix fragilis. Journal of the Marine Biological Association of the United Kingdom, 51/2: 267-282. Accessed August 24, 2012 at http://journals.cambridge.org/action/displayAbstract;jsessionid=FB095F7324DC20B690382D64367746FF.journals?fromPage=online&aid=5535888.

de Kluijver, M., S. Ingalsuo. 2012. "Common Brittle Star (Ophiothrix fragilis)" (On-line). Marine Species Identification Portal. Accessed August 24, 2012 at http://species-identification.org/species.php?species_group=echinodermata&id=100.

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