Sea Urchin Types and Species:

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Purple-Spined Sea Urchin

There are about 950 species of sea urchin; They live on substrates of every ocean and inhabit every depth zone from the intertidal seashore down to 5,000 meters (16,000 feet). The term "sea urchin" refers to the "regular echinoids", which are symmetrical and globular, and includes several different taxonomic groups, with two subclasses : Euechinoidea ("modern" sea urchins, including irregular ones) and Cidaroidea or "slate-pencil urchins", which have very thick, blunt spines, with algae and sponges growing on them. The "irregular" sea urchins are an infra-class inside the Euechinoidea, called Irregularia, and include Atelostomata and Neognathostomata. Irregular echinoids include: flattened sand dollars, sea biscuits, and heart urchins. [Source: Wikipedia

Red sea urchins (Scientific name: Strongylocentrotus franciscanus) are largest sea urchins, based on test size, with a maximum “test”, or outer skeleton, diameter of more than 18 centimeters (7 inches) and a maximum spine length of 8 centimeters (3.1 inches). Their test is made up of 10 fused plates that encircle the sea urchin like the slices of an orange. Every other section has holes through which the sea urchin can extend its tubed feet. Also known giant as red sea urchins, these colorful creatures varying between a uniform red and dark burgundy, that crawl slowly over the sea bottom using their spines as stilts. These sea urchin are often found in colder water such as off Alaska.[Source: Marine Bio]

The European edible sea urchin, Echinus esculentus, is listed as Endangered by the International Union for Conservation of Nature (IUCN).

Websites and Resources: Animal Diversity Web (ADW); National Oceanic and Atmospheric Administration (NOAA); Fishbase; Encyclopedia of Life; Smithsonian Oceans Portal ; Monterey Bay Aquarium ; MarineBio; Websites and Resources on Coral Reefs: Coral Reef Information System (NOAA) ; International Coral Reef Initiative ; Coral Reef Alliance ; Global Coral reef Alliance ; Global Coral Reef Monitoring Network

Purple-Spined Sea Urchin

Purple sea urchins (Scientific name: Arbacia punctulata) are native to the Atlantic Ocean and the Caribbean Sea. They are common from Cape Cod to the West Indies and are found mostly on rocks and shells but also can seen on reefs. They somewhat deep salt water but have observed from low-tide line to depth of about 230 meters (750 feet). [Source: Stephanie Braccini, Animal Diversity Web (ADW) /=]

Purple sea urchins have deep purple spines and bodies.Their body area, called a test, can grow to a diameter of 3-5 centimeters. This test is made up of ten fused plates that encircle the urchin. Each of these fused plates has small holes from which the feet extend.

There are male and female purple urchins. The females can release as many as several million eggs at a time. These eggs settle and the sperm released from the males swims and finds the eggs, fertilizes them and creates a large gamete. The larvae that hatches is bilaterally symmetrical, and changes to radial symmetry (symmetry around a central axis) after it grows. /=\

Purple sea urchins move on their tube feet and spines. They are able to speed up by creating a small suction at the end of their feet by pulling water out through an opening called a madroporite. They are able to regrow broken off spines. When not feeding, theyhide in holes in worn rocks or under shells. They have been observed, to even dig their own holes and wear away at the rocks until they are worn enough to be 'comfortable' and then they will reside in that hole until the current changes or they move. /=\

Long-Spined Sea Urchin

Rock-boring urchin

Long-spined sea urchins (Scientific name:Diadema antillarum) are distributed in shallow waters of the Caribbean Sea, particularly around the Bahamas, in the Western Atlantic from eastern Florida to Brazil and in the Eastern Atlantic around Madeira, the Gulf of Guinea, the Canary Islands, Cape Verde, and the Annabon islands. Long-spined sea urchins prefer quiet waters, and are often seen in coral reefs as well as in turtle grass beds and on rock bottoms. They are typically found at depths of from the ocean surface to 400 meters (,1312 feet). The lifespan of Long-spined sea urchins are closely related to temperatures and food availability. Those in warmer climates tend to have a quicker rate of development and shorter lifespan than those in colder climates. Their average lifespan in the wild is six years. [Source: Erin Puckett, Animal Diversity Web (ADW) /=]

Long-spined sea urchins have a regular round sea urchin shape. Adults have sea urchins can reach up to 50 centimeters (1.6 feet) in diameter. Their spines range from 30 to 40 centimeters (one to 1.3 feet) in length and can be up to four times the diameter of the test (body). The spines are thin, hollow, and break easily. The test is rigid and there is a reduced amount of soft tissue in the body wall as compared to other sea urchin species. The test and spines of a mature adult are typically black, but lighter colored spines may be intermixed. The spines of juveniles are banded with black and white. When the urchin dies, the spines falls off and the test remains. /=\

Long-spined sea urchins grazes on the algal turf of coral reefs primarily during the night. Foods eaten include algal turf, young corals and zoanthids. Their main known predators are queen triggerfish. They are also consumed by Caribbean spiny lobsters, Caribbean helmets and two species of toadfish. The spines of Long-spined sea urchins are brittle and fragmentize. The pieces are difficult to remove, and often cause infections as they carry bacteria. The mucous coating of the spines, normally used to kill organisms that live in the spines, carries a mild poison that also aids in deterring smaller predators. Long-spined sea urchins have been observed to gather in groups as an added protection.

Long-spined sea urchins feeds on the algal turf of the coral reefs. The algal turf grows rapidly, and without the urchin's control, can desstroy corals. Llong-spined sea urchins clears the reefs, making room for coral larvae to settle and grow. However, the urchin actually wears away at the calcium carbonate of the reef, too.

Long-Spined Sea Urchin Behavior and Reproduction

Long-spined sea urchins are very active urchin. They have a high reactivity and sensitivity to changes in light and water disturbances and wave their spines in the direction of things that disturb them and quickly retreat to sheltered areas if necessary. [Source: Stephanie Braccini, Animal Diversity Web (ADW) /=]

Long-spined sea urchins are also extremely sensitive to light. The hide away in darker areas, like crevices in the reef, during the day, and emerges at night to feed. Groups of individuals can be found in open areas, and densities can reach up to 20 per square meter. This group size corresponds to the abundance of predators in the area.

Long-spined sea urchins sense using vision, touch and chemicals usually detected with smell and communicate with chemicals usually detected by smelling and photic-bioluminescence. These sea urchin have highly developed light sensitivity. When a shadow appears, the urchin waves its spines in the direction of the shadow and moves away from the shadow. In this way, long-spined sea urchins can 'see' predators.

The spawning of long-spined sea urchins appears to be connected to temperature and the lunar calendar. During the summer breeding season, eggs and sperm are released once during each lunar month. This spawning period is dependant upon temperature. Some groups of long-spined sea urchins have been observed congregating during their spawning season. The egg and sperm are released into the water where they are fertilized and develop into the larval echinopluteus. Egg size has also been observed to change during the month. Spawning occurs when the eggs are largest.

Long-Spined Sea Urchin

Rock Boring Urchins

Rock-boring urchins (Scientific name: Echinometra lucunter) are also known as red rock urchin, but these names have also been applied to species such as Echinometra mathaei and Echinometra oblonga. Rock-boring urchins (here referring to Echinometra lucunter) live throughout the Caribbean and coastal South Atlantic subtropical region, from Bermuda through southern Florida and the islands of the Caribbean (particularly Barbados) to Desterra, Brazil.[Source: Julio Plazas, Animal Diversity Web (ADW) /=]

Rock-boring urchins are typically found at depths of zero to 45 meters (148 feet). They are most abundant on tidal terraces and rocky shores in areas of relatively wave activity and on shallow coral reefs. They like to hide out in rock crevices, and are also on sandy bottoms. This species can survive exposure to direct sunlight for up to three hours although water temperatures of over 38°C are lethal. (Abbott, et al., 1974) /=\

Rock-boring urchins grow slowly. If they make it through their first year of life, their average life expectancy is over 10 years. They are venomous and inject toxin via their spines. In Brazil they is responsible for approximately half of all accidents caused by marine animals. Effects of the venom range from mild, temporary discomfort to pain and secondary infections lasting for weeks. Rock-boring urchins are not considered endangered or threatened. They have not been evaluated for the International Union for Conservation of Nature (IUCN) Red List. They have no special status according to the Convention on the International Trade in Endangered Species (CITES).

Rock-boring urchins help the ecosystems they live in creating habitat and fostering biodegradation. They are considered a keystone species, meaning their presence or absence strongly affects populations of other species in area where they live. According to Animal Diversity Web: This species affects the development of coral reefs through shading, physical abrasion, and incidental ingestion of sessile (fixed in one place) epifauna, thus altering the community's physical and biological structure. Because it is mainly herbivorous, it has a strong impact on algal biomass, affecting the biodiversity and functionality of its ecosystem by increasing the access to substrate for the settlement, attachment and growth of other benthic (bottom-dwelling) organisms. In Brazil, reduction of algal cover helped recruitment of sponges . /=\

Rock Boring Urchin Characteristics and Behavior

The tests (bodies without spines) of rock-boring urchins range in length from four four to five centimeters (1.6 to 5.9 inches) although some individuals over 15 centimeters have been recorded.. These sea urchins have an elliptical shape with 100 to 150 colored spines on the arboral surface. Test color is variable, ranging between a black, brown, green or dark blue color with lighter colors on the arboral surface. In some cases the apical system of the test is bright red, with black spines. This species is differentiated from other closely related species by having fewer pore-pairs per arc, fewer ambulacral and interambulacral plates, a different apical system, and slender, tridentate pedicellariae. [Source: Julio Plazas, Animal Diversity Web (ADW) /=]

Rock-boring urchins are nocturnal (active at night), motile (move around as opposed to being stationary), sedentary (remain in the same area), solitary, territorial (defend an area within the home range) and social (associates with others of its species; forms social groups). The size of their range territory is zero to three square meters. This species may occur in population densities of up to 240 individuals per 2.6 square kilometers. Individuals have been documented to travel between zero and three square meters over a period of four days. /=\

This species uses its tube feet to attach itself to rocky surfaces and it has the ability to create its own burrows. Most movements occur during dark hours, when urchins move out of crevices and rock burrows to feed, primarily on algae, and then return to them for shelter. This species also exhibits territorial (defend an area within the home range), and agonistic behaviors to defend its shelter and access to food from members of their own species. However, it can coexist with congeners such as Echinometra viridis without competing for food or resources.

Rock Boring Urchin Feeding and Predators

Rock-boring urchins are omnivorous species, using its arboral spines to trap food and carry it to the oral surface where they use a specialized feeding apparatus (Aristotle's lantern) to graze and consume their food. They are primarily herbivores (primarily eat plants or plants parts) and algivore (eats algae) but on occasion also eat animal material and detritus ( decomposed plants and/or animals).

According to Animal Diversity Web: Approximately 45 percent of the diet consists of algae attached to the urchin's burrows and the remainder is algal drift. Some of the macrophytic algae known to be consumed by this species include Dictyota sp., Chaetomorpha sp., Sargassum sp. and Laurencia papilosa, and it is also known to consume seagrasses in the genera Thalassia and Syringodium. Gut contents of some urchins have been observed to include spines from other echinoids (resulting from territorial fights), and sessile invertebrates.[Source: Julio Plazas, Animal Diversity Web (ADW) /=]

Predators of rock-boring urchins include fishes, birds, molluscs, and humans. Triggerfish are able to break urchin tests with their strong jaws and consume the viscera, while gobies consume the urchin's tube feet and pedicellarie. Shorebirds, such as ruddy turnstones, flock over exposed reefs during low tide, pecking through urchin peristomes and eating the viscera. Conch use their radulae to drill through the urchin tests. This species is able to detect some invertebrate predators' odors and chemical signals, helping it to avoid predation. When attacked, an urchin waves its spines and tube feet as a defense and escape mechanism.

Their main known predators are black margate (Anisotremus surinamensis), ruddy turnstone (Arenaria interpres morinella), queen triggerfish (Balistes vetula), king helmet conch (Cassis tuberosa), spot-fin porcupinefish (Diodon hystrix), nineline goby (Ginsburgellus novemlineatus), Hairy blenny (Labrisomus nuchipinnis) and humans Homo sapiens)

Rock Boring Urchin Mating, Reproduction and Offspring

Rock-boring urchins are oviparous(young are hatched from eggs) and iteroparous (offspring are produced in groups). They engage in external reproduction in which sperm from the male fertilizes the female’s egg outside her body and employ broadcast (group) spawning, the main mode of reproduction in the sea. It involves the release of both eggs and sperm into the water and contact between sperm and egg and fertilization occur externally. [Source: Julio Plazas, Animal Diversity Web (ADW) /=]

Rock-boring urchins are oviparous engage in seasonal breeding. Typically they breed once per year; occasionally twice per year The breeding season is in the spring and summer. There is no parental involvement in the raising of offspring. After the eggs are released, zygotes become planktonic larvae and drift unattended until they develop into the benthic (bottom-dwelling) adult form.

Rock-boring urchins are polygynandrous (promiscuous), with both males and females having multiple partners. These sea urchins are usually found in dense aggregations. Individuals release their eggs and sperm into the water column, with males usually spawning before females. The male’s release may act as a cue, stimulating females to release eggs.

According to Animal Diversity Web: Sexual maturity occurs when individuals reach a test diameter of at least 20 millimeters and when ripe sex cells are present in the sex organs. Sex organ development occurs most often during spring, with spawning occuring in the summer, usually once but in some cases twice per year. The sex organal index (number of sex cells/unit of sex organ tissue) is highest during summer. The gametogenic cycle comprises five different stages: proliferative, premature, mature, depleted, and resting. Release of the male’s spermatozoa elicits release of oocytes by females. Spawning may also occur during other times of the year outside of summer, depending primarily on hydrodynamics and nutrient availability. There is currently no published information noting the average number of offspring, gestation period, and birth mass for this species.

Image Sources: Wikimedia Commons, NOAA

Text Sources: Animal Diversity Web (ADW); National Oceanic and Atmospheric Administration (NOAA); Wikipedia, National Geographic, Live Science, BBC, Smithsonian, New York Times, Washington Post, Los Angeles Times, The New Yorker, Reuters, Associated Press, Lonely Planet Guides and various books and other publications.

Last Updated May 2023

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