''Echinometra viridis'', the reef urchin, is a

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

sea urchin Sea urchins or urchins () are echinoderms in the class (biology), class Echinoidea. About 950 species live on the seabed, inhabiting all oceans and depth zones from the intertidal zone to deep seas of . They typically have a globular body cove ...

in the

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

Echinometridae The Echinometridae are a Family (biology), family of sea urchins in the class (biology), class Echinoidea. Characteristics All Echinometridae have imperforate tubercles and compound ambulacral plates.test Test(s), testing, or TEST may refer to: * Test (assessment), an educational assessment intended to measure the respondents' knowledge or other abilities Arts and entertainment * ''Test'' (2013 film), an American film * ''Test'' (2014 film) ...

(shell) covered with medium length spines. These are greenish in colour with paler bases and darker, often violet, tips. This urchin grows to a diameter of with the longest spines being . It looks very similar to the rock-boring urchin '' Echinometra lucunter'', but the dark tips and the greater length of the spines are distinctive.

Distribution

The reef urchin is found on reefs in the

Caribbean Sea The Caribbean Sea is a sea of the Atlantic Ocean, North Atlantic Ocean in the tropics of the Western Hemisphere, located south of the Gulf of Mexico and southwest of the Sargasso Sea. It is bounded by the Greater Antilles to the north from Cuba ...

from southern

Florida Florida ( ; ) is a U.S. state, state in the Southeastern United States, Southeastern region of the United States. It borders the Gulf of Mexico to the west, Alabama to the northwest, Georgia (U.S. state), Georgia to the north, the Atlantic ...

Venezuela Venezuela, officially the Bolivarian Republic of Venezuela, is a country on the northern coast of South America, consisting of a continental landmass and many Federal Dependencies of Venezuela, islands and islets in the Caribbean Sea. It com ...

at depths down to about . It is not as common as the rock-boring urchin and seems to be absent from the

West Indies The West Indies is an island subregion of the Americas, surrounded by the Atlantic Ocean, North Atlantic Ocean and the Caribbean Sea, which comprises 13 independent island country, island countries and 19 dependent territory, dependencies in thr ...

to the east of the

Virgin Islands The Virgin Islands () are an archipelago between the Atlantic Ocean, North Atlantic Ocean and northeastern Caribbean Sea, geographically forming part of the Leeward Islands of the Lesser Antilles in the Caribbean, Caribbean islands or West Indie ...

Biology

The reef urchin conceals itself in crevices or under boulders. It emerges at night to feed by grazing on algae with its five teeth, part of the

Aristotle's lantern Sea urchins or urchins () are echinoderms in the class (biology), class Echinoidea. About 950 species live on the seabed, inhabiting all oceans and depth zones from the intertidal zone to deep seas of . They typically have a globular body cove ...

organ that surrounds its mouth. It is not believed to bore holes, but its grazing still causes

bioerosion Bioerosion describes the breakdown of hard ocean substrates – and less often terrestrial substrates – by living organisms. Marine bioerosion can be caused by mollusks, polychaete worms, phoronids, sponges, crustaceans, echinoids, ...

in reefs. In Panama, breeding takes place during the period April to December. It does not seem to be correlated with the phases of the moon as in some other sea urchin species. Fertilisation is external and the echinopluteus

larva A larva (; : larvae ) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect development such as insects, some arachnids, amphibians, or cnidarians typically have a larval phase ...

e are

plankton Plankton are the diverse collection of organisms that drift in Hydrosphere, water (or atmosphere, air) but are unable to actively propel themselves against ocean current, currents (or wind). The individual organisms constituting plankton are ca ...

ic. When these settle, they undergo a rapid

metamorphosis Metamorphosis is a biological process by which an animal physically develops including birth transformation or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and different ...

into juvenile sea urchins. Researchers have studied the likely effect on the reef urchin of a rise in the

carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...

levels which are likely to increase

ocean acidification Ocean acidification is the ongoing decrease in the pH of the Earth's ocean. Between 1950 and 2020, the average pH of the ocean surface fell from approximately 8.15 to 8.05. Carbon dioxide emissions from human activities are the primary cause of ...

by the end of the 21st century. It was found that the urchins would be negatively impacted because of decreased calcification, lowering their ability to build their

tests Test(s), testing, or TEST may refer to: * Test (assessment), an educational assessment intended to measure the respondents' knowledge or other abilities Arts and entertainment * ''Test'' (2013 film), an American film * ''Test'' (2014 film) ...

, especially during winter and in the more northerly parts of their range.

Ecology

The reef urchin is an important grazer on fleshy algae in the Caribbean area. Its abundance is reduced by predation by fish, especially the jolthead porgy ('' Calamus bajonado''), the queen triggerfish ('' Balistes vetula''), the ocean triggerfish ('' Canthidermis sufflamen'') and the hogfish ('' Lachnolaimus maximus''). Because of this predation, the reef urchin avoids open reef flats and in these locations there is an overgrowth of fleshy algae. It is unable to take over the algal controlling role of the black sea urchin ('' Diadema antillarum'') which is subject to great fluctuations in population.

References

{{Taxonbar, from=Q937376 Echinometridae Echinoderms described in 1863 Taxa named by Alexander Agassiz