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)
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)
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)
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)
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)
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)
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)
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.
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)
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)
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)
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)
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)
Diadema savignyi is not listed on the Red List, CITES appendices, or Endangered Species Act list.
Kathleen Elmquist (author), University of Michigan-Ann Arbor, Phil Myers (editor), University of Michigan-Ann Arbor, Renee Mulcrone (editor), Special Projects.
Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.
living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.
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.
uses smells or other chemicals to communicate
the nearshore aquatic habitats near a coast, or shoreline.
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.
particles of organic material from dead and decomposing organisms. Detritus is the result of the activity of decomposers (organisms that decompose organic material).
animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature
fertilization takes place outside the female's body
union of egg and spermatozoan
A substance that provides both nutrients and energy to a living thing.
An animal that eats mainly plants or parts of plants.
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.
the area of shoreline influenced mainly by the tides, between the highest and lowest reaches of the tide. An aquatic habitat.
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.
the area in which the animal is naturally found, the region in which it is endemic.
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.
found in the oriental region of the world. In other words, India and southeast Asia.
the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.
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).
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.
mainly lives in oceans, seas, or other bodies of salt water.
remains in the same area
reproduction that includes combining the genetic contribution of two individuals, a male and a female
places a food item in a special place to be eaten later. Also called "hoarding"
uses touch to communicate
the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.
breeding takes place throughout the year
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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.