Ophiactis savignyi, like other ophiuroids, perceives the environment by chemosensors in its tube feet. This brittle star is also able to detect very dilute concentrations of amino acids, and vitamins, which allows it to detect food and predators. Ophiactis savignyi responds to damage-release alarm signals. A divergence in response time to chemical alarm signals occurs between algae and sponge dwelling individuals of the species. Individuals dwelling in an algae habitat respond to conspecific (interspecies) and heterospecific (among different species) signals. Sponge dwelling individuals have little response to heterospecific signals. Sponge dwelling O. savignyi are better protected from predators and do not have as much environmental pressure as their algae dwelling members. This species also exhibits negative phototaxis (move away from light), and senses light from light-sensitive cells in skeletal plates within its dermis.
Communication Channels: chemical
Other Communication Modes: pheromones
Perception Channels: visual ; tactile ; chemical
The tropical brittle star, O. savignyi, is not considered endangered. This species has a global distribution in tropical and subtropical regions, and is very abundant.
US Federal List: no special status
CITES: no special status
State of Michigan List: no special status
The newly fertilized eggs of O. savignyi turn into ophiopluteus larvae. The larvae have a crystalline skeleton, are bilateral, and free-swimming. The exact amount of time before metamorphosis into a radial, benthic adult is unknown, but it is estimated to be a month. Individuals produced by fission regenerate into two adult organisms.
Development - Life Cycle: metamorphosis
This species has no negative impact on humans or economic importance to them.
Ophiactis savignyi has no significant positive impact on humans.
Ophiactis savignyi dominates sponge habitats and competes with other brittle stars for space. In the Caribbean it inhabits at least ten species of sponges. This brittle star also inhabits various algae. Numbers are greater in sponges than in algal turf, probably because sponges provide a better refuge against predators. Other than providing food for species of fish, shrimp, and crab, the species at times occludes the excurrent siphon of sponges, which is potentially harmful. Ophiactis savignyi acts as a detritivore and recycles dead plankton, bacteria, small crustaceans, and invertebrates.
Algae that O. savignyi inhabit include Hypnea species. Sponges that O. savignyi inhabit include Haliclona species, Tedania ignis, Scopalina ruetzleri, and Amphimedon viridis.
Ecosystem Impact: biodegradation
Ophiactis savignyi is detritophagous, i.e., it feeds mainly on small particles of detritus. The stomach typically contains foraminiferans, bryozoans, organic detritus, and small gastropods. This brittle star is a suspension feeder using its tube feet to catch small particles and moving them toward its mouth. Ophiactis savignyi is also characterized as a deposit feeder, cleaning the outer surface of its habitat and filtering food from the water. A large individual suspension feeds by raising its arms into the water column. Ophiactis savignyi will also situate itself at the base of the excurrent pore of a sponge to collect food particles.
Animal Foods: mollusks; aquatic crustaceans; other marine invertebrates; zooplankton
Plant Foods: bryophytes; phytoplankton
Other Foods: detritus
Foraging Behavior: filter-feeding
Primary Diet: carnivore (Eats non-insect arthropods, Molluscivore , Eats other marine invertebrates); herbivore (Algivore); detritivore
Ophiactis savignyi can be found in tropical marine habitats around the globe. Humans may have contributed to the dispersal of O. savignyi, especially in the western and eastern populations around the Isthmus of Panama. The species was separated by the isthmus until humans opened it with the Panama Canal. Ophiactis savignyi is found in the Pacific, the Atlantic Oceans, the Persian Gulf, and the Mediterranean Sea. Its ranges also include the northern, western, and eastern coasts of South America, Hawaii, French Polynesia, the Gulf of Mexico, the Caribbean, and the south-eastern and south-western coasts of North America. The brittle star is also along the coast of Australia and Southeast Asia extending up into China's eastern coast. This species is considered the most common brittle star in the world.
Biogeographic Regions: nearctic (Native ); palearctic (Native ); oriental (Native ); ethiopian (Native ); neotropical (Native ); australian (Native ); indian ocean (Native ); atlantic ocean (Native ); pacific ocean (Native ); mediterranean sea (Native )
Other Geographic Terms: cosmopolitan
Ophiactis savignyi is benthic and resides inshore, on continental shelves, and continental slopes. This brittle star shelters itself in various subtropical marine and tropical marine habitats, including rubble, algae, corals, sponges, reefs, mangrove areas, ship hulls, and sea grasses like turtle grass. Ophiactis savignyi is more frequent on sponges than algae. This species can inhabit sponges in densities up to 1,892 individuals per 100 grams of dried sponge; 3,000 individuals per liter have also been reported. The density of O. savignyi depends on space and food available. One species of sponge inhabited by this brittle star is Tedania ignis; an inhabited algae species is Sargassum cymosum.
Range depth: 1 to 518 m.
Average depth: 259 m.
Habitat Regions: tropical ; saltwater or marine
Aquatic Biomes: benthic ; reef ; coastal
No information on the lifespan was found.
Ophiactis savignyi is radially symmetric as an adult, and is generally found with six arms, but can be found with 1-7 arms. Individuals with fewer arms are in the process of regeneration. Like other ophiuroids, O. savignyi has arms that are sharply demarcated from the central disk. The arms are jointed and flexible and are usually variegated with intermittent dark and light markings. The animal's color ranges from mixes of green, brown, white, yellow, and cream. The oral surface is lighter than the aboral surface. Australian members of this species have a brown disc with bright yellow arms, but the species is usually green or blue. The disc of the animal is 3.8-5 mm and darkly pigmented with rough-tipped spines on top of the disc. The arms of the animal range from 16.3 mm-20 mm and have small, rough spines running along them. The oral surface of the central disc contains one to three oral papilliae that are flat and scaly. In O. savignyi, fission causes species to have a variable number of arms; specimens that recently split typically have three large arms and three small regenerating ones.
Sexual reproduction results in planktonic ophiopluteus larvae that have bilateral symmetry. They are v-shaped and have a crystalline skeleton with curving ciliated bands for feeding. Ophiopluteus larvae are free swimming until they metamorphose into adults.
Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry ; radial symmetry
Sexual Dimorphism: sexes alike
A defense mechanism of O. savignyi is its use of autonomy (casting off of limbs) when escaping predators. It also is capable of regenerating them. Negative phototaxis and damage-release alarm signals are also evolved characteristics to escape predators. A fish may bite the brittle star into smaller pieces before consuming it, so the ability to lose and regenerate limbs is an advantage. This species is prey to crabs and shrimp.
Known Predators:
Sexual reproduction by O. savignyi involves broadcast spawning. Each sex scatters its gametes in the water column. During sexual reproduction gametes from different colonies presumably mix. Sexual reproduction is followed by asexual reproduction via fission. The majority of individuals lose the ability to reproduce sexually after splitting. Sexual reproduction, in summer and fall, is usually followed by asexual reproduction. The separation of these two breeding modes may be because after splitting, O. savignyi must regenerate its lost limbs, which takes away from its ability to produce eggs and sperm. In both sexes the gametes of one or both of the newly divided brittle stars are reabsorbed. When O. savignyi reaches a large enough size, at least a 3.0 mm disc, it begins to spawn sexually.
Mating System: polygynandrous (promiscuous)
Ophiactis savignyi reproduces either through asexual splitting or sexual broadcast spawning. Asexual reproduction occurs by voluntary splitting down the organism's central disc, producing two halves, which regenerate into two functioning organisms; this and predation accounts for odd number of limbs found in some individuals. In O. savignyi simultaneous asexual and sexual reproduction is also known to occur, but mature gonads are usually reabsorbed in one or both freshly split clones, making simultaneous sexual reproduction unlikely.
Sexual maturity of O. savignyi appears to depend on size. Ophiactis savignyi displays a difference in sex ratio that results in a higher proportion of males than females. This difference may be due to a greater investment in gonad mass by females. Males are more likely to retain their ability to reproduce after splitting than females, which may be the cause of the male biased sex ratio. Sexual spawning may result in long-distance colonization of sponges and algae by brittle stars and would also account for the unusual sex ratio; a single organism can generate an entire colony. In Harrington Sound, a sponge colony was found with an all male sex ratio that supports this hypothesis.
Breeding interval: Asexual and sexual year round, but sexual more frequent late summer to fall.
Key Reproductive Features: year-round breeding ; sexual ; asexual ; fertilization (External ); broadcast (group) spawning
Ophiactis savignyi does not have any parental investment. When large enough the organism reproduces sexually. Immature and mature organisms reproduce by splitting with both halves being autonomous.
Parental Investment: no parental involvement
