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 ; chemical
Perception Channels: tactile ; chemical
Diadema savignyi is not listed on the Red List, CITES appendices, or Endangered Species Act list.
US Federal List: no special status
CITES: no special status
State of Michigan List: no special status
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
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
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
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.
Mutualist Species:
Commensal/Parasitic Species:
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.
Plant Foods: algae
Other Foods: detritus
Foraging Behavior: stores or caches food
Primary Diet: herbivore (Algivore)
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 (Native ); ethiopian (Native ); australian (Native ); oceanic islands (Native ); indian ocean (Native ); pacific ocean (Native )
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.
Range depth: 1 to 10 m.
Habitat Regions: tropical ; saltwater or marine
Aquatic Biomes: reef ; coastal
Other Habitat Features: intertidal or littoral
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.
Typical lifespan
Status: wild: 3 to 5 years.
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.
Average mass: 120 g.
Range length: 61 to 90 mm.
Other Physical Features: ectothermic ; heterothermic ; radial symmetry
Sexual Dimorphism: sexes alike
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.
Known Predators:
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)
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).
Breeding interval: Diadema savignyi breeds once a month.
Breeding season: All year
Key Reproductive Features: year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (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)
