Diadema savignyi

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.

• Biogeographic Regions
• oriental oriental
  • native native
• ethiopian ethiopian
  • native native
• australian australian
  • native native
• oceanic islands oceanic islands
  • native native
• indian ocean
  • native native
• pacific ocean pacific ocean
  • native native

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.

• Habitat Regions
• tropical tropical
• saltwater or marine saltwater or marine

• Aquatic Biomes
• reef reef
• coastal coastal

• Other Habitat Features
• intertidal or littoral intertidal or littoral

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.

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.

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

• Sexual Dimorphism
• sexes alike

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.

• Development - Life Cycle
• metamorphosis metamorphosis

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.

• Mating System
• polygynandrous (promiscuous) polygynandrous (promiscuous)

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).

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

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.

• 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.

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.

• Key Behaviors
• sedentary sedentary
• colonial colonial

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.

• Communication Channels
• tactile tactile
• chemical chemical

• Perception Channels
• tactile tactile
• chemical chemical

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.

• Primary Diet
• herbivore herbivore
  • algivore

• Plant Foods
• algae

• Other Foods
• detritus detritus

• Foraging Behavior
• stores or caches food stores or caches food

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.

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.

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.

• Positive Impacts
• food 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.

• Negative Impacts
• injures humans

Conservation Status

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

Additional Links

Encyclopedia of Life

Contributors

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

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 Echinoderms . Lisse: CRC Press.

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

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 .

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.

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.