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Diadema savignyi

By Kathleen Elmquist

Geographic Range

Diadema savignyi lives in shallow waters off of the east coast of Africa near Madagascar, Tanzania, and Kenya. It is found widespread across the Indo-Pacific region such as North Australia, the Philippines, China, South Japan, East Indies, South Pacific Islands, and islands in the western Indian Ocean. (Muthiga, et al., 2007; Muthiga, 2003)

Habitat

Diadema savignyi lives in sand flats and coral reef areas, which are warm shallow areas near coasts. This urchin lives successfully in crevices, but is also found in aggregate groups on the sandy ocean floor or individually hidden under heads of coral. (Hoey, 2008; Muthiga, et al., 2007)

  • Range depth
    1 to 10 m
    3.28 to 32.81 ft

Physical Description

Diadema savignyi is an urchin that that displays pentamerism, which is a quality of the class Echinodermata. This urchin has a round body (test) with many long spines, tube feet, and a dark anal sac. The test can grow to 90 mm in diameter. (Coppard and Cambell, 2006; Hoey, 2008)

Diadema savignyi is sympatric with the species Diadema setosum. The difference between these two species is coloration. Diadema savignyi has solid iridescent blue or sometimes green lines that run along its black test and periproct (area surrounding anus) and D. setosum has dotted blue lines along its test and an orange line around its periproct. (Muthiga, 2003; Muthiga, et al., 2007)

  • Sexual Dimorphism
  • sexes alike
  • Average mass
    120 g
    4.23 oz
  • Range length
    61 to 90 mm
    2.40 to 3.54 in

Development

The female releases her eggs in the water column on the same day that the males release sperm. The eggs are fertilized and develop into pluteus larvae. The time D. savignyi takes to form a blastula and turn into a larva is unknown, but development depends on temperature, food availability, and salinity. In D. setosum the blastula develops into a blastua in 6 hours and an early plutei within 35 hours depending on environmental conditions. The larva is complex and pelagic, feeding with a cilliated feeding-band structure. Nerves are located along the cilliated band and the esophogus. The larva has bilateral symmetry with left-right arm pairs that are supported by calcareous skeletal rods. When the larva ages, parts of the band become isolated and specialized for locomotion. A late-stage larva has pedicellariae. The pluteus contains a complete gut. After this larval stage, the organism transforms into an adult. The amount of time D. savignyi is in the larval stage is unknown, but in a similar species D. setosum the stage is 6 weeks long. (Miner and Edward, 2001; Muthiga, et al., 2007)

Reproduction

Sea urchins spawn by gathering together and releasing millions of eggs and sperm into the water column. An urchin does not have a specific mate or a social structure. Diadema savignyi spawns once a month in coordination with the lunar cycle. Diadema savignyi may interbreed with D. setosum, but this rarely occurs because the species spawn at different times in the lunar cycle. (Muthiga, et al., 2007)

Diadema savignyi has separate sexes that show no external sexual differences. It reproduces throughout the year and reproduction peaks at different times. Diadema savignyi reproduces monthly after the full moon during lunar days 17 and 18. The males produce spermatocytes over the course of a month by the process spermatogenesis. Oogenesis in females is also a month long process to create eggs (ova). (Muthiga, et al., 2007)

  • Breeding interval
    Diadema savignyi breeds once a month.
  • Breeding season
    All year

There is no specific information about parental care for the species D. savignyi. No members of the genus Diadema provides parental care. Individuals release eggs and sperm into the water column leaving the eggs to be fertilized, sink to the bottom, and develop into larvae. (Muthiga, et al., 2007)

  • Parental Investment
  • no parental involvement
  • pre-fertilization
    • provisioning

Lifespan/Longevity

Diadema savignyi has a high initial growth rate compared to D. setosum, but both species reach a similar size. Diadema savignyi has a short lifespan of 3 to 5 years. The results above are from a study performed on caged indivuals off the coast of Kenya. (Muthiga, et al., 2007)

  • Typical lifespan
    Status: wild
    3 to 5 years

Behavior

Diadema savignyi is a solitary species that moves less than 1 meter. This urchin hides most of the day and moves at night to forage for algae to eat. This species lives in high population densities and individuals move closer together to increase fertilization.

Communication and Perception

Diadema savignyi does not communicate in order to mate. Both sexes release gametes from lunar cues. It does not have sense organs so it hides during the day and only moves a maximum of 1 meter to forage for food at night. (Muthiga, 2003; Muthiga, et al., 2007)

Food Habits

Diadema savignyi grazes on algae. It uses teeth that are on an apparatus called Aristotle's Lantern to scrape the algae off of hard substrate such as rocks or dead coral substrate. (Hoey, 2008)

  • Plant Foods
  • algae

Predation

Species of Diadema are predated upon by 15 species of finfish, the spiny lobster, and 2 species of gastropods. The finfish are mostly species with hard palates such as members of the families Balistidae and Diodontidae. The study performed analysis on gut contents, but did not observe predation specifically on D. savignyi. The presence of more urchin species in a reef area increase the density of urchins and then predation intensity by Balistidae decreases. (Muthiga, et al., 2007; Shafir and McClanahan, 1990)

Ecosystem Roles

Diadema savignyi is important to reef ecosystems because it grazes algae and prevents the algae from blocking coral from receiving light. When a study was performed to reduce the number of D. savignyi the reduction had a large effect on fish and algal biomass. (Muthiga, et al., 2007)

Mutualist Species
  • Corals
Commensal/Parasitic Species
  • No commensals or parasites.

Economic Importance for Humans: Positive

Many people eat sea urchins around the world, but this custom is restricted to a few species. There is no information whether D. savignyi is eaten, but a closely related species D. setosum is eaten in a few districts of Kyushu Island. This species is only eaten in a few places because it is not very palatable. (Muthiga, et al., 2007)

  • Positive Impacts
  • food

Economic Importance for Humans: Negative

Diadema savignyi and other species of Echinoidea can inflict some injury to people. The long spines can penetrate the skin when a person steps or falls onto an urchin. An infection can occur, similar to a foreign-body reaction if a spine detaches and is lodged in body tissue. The reaction occurs if the spine takes time to be forced to the surface of the skin. (Alender and Russel, 1966)

  • Negative Impacts
  • injures humans

Conservation Status

Diadema savignyi is not listed on the Red List, CITES appendices, or Endangered Species Act list.

Contributors

Kathleen Elmquist (author), University of Michigan-Ann Arbor, Phil Myers (editor), University of Michigan-Ann Arbor, Renee Mulcrone (editor), Special Projects.

Glossary

Australian

Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

World Map

Ethiopian

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

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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

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.

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

food

A substance that provides both nutrients and energy to a living thing.

herbivore

An animal that eats mainly plants or parts of plants.

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.

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.

native range

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

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.

oriental

found in the oriental region of the world. In other words, India and southeast Asia.

World Map

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.

sedentary

remains in the same area

sexual

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

stores or caches food

places a food item in a special place to be eaten later. Also called "hoarding"

tactile

uses touch to communicate

tropical

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

year-round breeding

breeding takes place throughout the year

References

Alender, C., F. Russel. 1966. Physiology of Echinodermata. New York: John Wiley & Sons.

Bak, R. 1990. Patterns of echinoid bioerosion in two Pacific coral reef lagoons. Marine Ecology Progress Seies, 66: 267-272.

Coppard, S., A. Cambell. 2005. Lunar periodicities of diadematid echinoids breeding in Fiji. Coral Reefs, 24: 324-332.

Coppard, S., A. Cambell. 2006. Taxonomic significance of test morphology in the echinoid genera Diadema Gray, 1825 and Echinothrix Peters, 1854 (Echinodermata). Zoosystema, 28: 93-112.

Cronin, G., V. Paul, M. Hay, W. Fenical. 1997. Are tropical herbivores more resistant than temperate herbivores to seaweed chemical defenses? Diterpenoid metabolites from Dictyota acutiloba as feeding deterrents for tropical versus temperate fishes and urchins. Journal of Chemical Ecology, 23: 289-302.

Hoey, J. 2008. "The effect of herbivory by the long-spined sea urchin, Diadema savignyi on algae growth in the coral reefs of Moorea, French Polynesia" (On-line pdf). Accessed May 17, 2011 at http://www.escholarship.org/uc/item/7xj4g5dm.

Lessios, H. 2001. Molecular phylogeny of Diadema: Systematic implications. Pp. 487-495 in E Barker, ed. Echinoderms. Lisse: CRC Press.

Miner, B., L. Edward. 2001. Larval and life-cycle patterns in echinoderms. Zoology, 79: 1125-1169.

Muthiga, N. 2003. Coexistence and reproductive isolation of the sympatric echinoids Diadema savignyi Michelin and Diadema setosum (Leske) on Kenyan coral reefs. Marine Biology, 143: 669-677.

Muthiga, N., T. McClanahan, J. Lawrence. 2007. Edible Sea Urchins:Biology and Ecology. New York: Elsevier Science. Accessed May 17, 2011 at http://books.google.com/books?id=6T2JomruARoC&lpg=PA205&ots=Zd4J59hiXO&dq=%22Diadema%20savignyi%22%20and%20conservation&lr&pg=PA205#v=onepage&q=%22Diadema%20savignyi%22%20and%20conservation&f=false.

Palumbi, S. 1994. Genetic divergence, reproductive isolation, and marine speciation. Annual Review of Ecological Systems, 25: 547-572.

Shafir, S., T. McClanahan. 1990. Causes and consequences of sea urchin abundance and diversity of in Kenyan coral reef lagoons. Oecologia, 83: 362-370.

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