Paracentrotus lividus
Encyclopedia
Paracentrotus lividus is a species
of sea urchin
in the family
Parechinidae
commonly known as the purple sea urchin. It is the type species
of the genus
and occurs in the Mediterranean Sea and eastern Atlantic Ocean.
with a diameter of up to seven centimetres. The test is densely clothed in long and sharply pointed spines that are usually purple but are occasionally other colours including dark brown, light brown and olive green. There are five or six pairs of pores on each ambulacral
plate. The tube feet
are in groups of 5 or 6, arranged in small arcs.
and in the eastern Atlantic Ocean
from western Scotland
and Ireland
to the Azores
, Canary Islands
and Morocco
. It is most common in the western Mediterranean, the coasts of Portugal
and the Bay of Biscay
, where the water temperature in winter varies between 10 and 15°C.
. It is found on rocks and boulders, and in seagrass
meadows of Zostera marina
and Posidonia oceanica
. Although Cymodocea nodosa
is a preferred food item, it is seldom found in meadows of this seagrass, perhaps because the shifting sand substrate does not suit it or because of pressure from predators
. In fact it avoids soft substrates and can sometimes be found clustered on stones or shell "islands" surrounded by sand. In shallow or exposed waters it can use its mouth and spines to dig into soft rocks to create cavities into which it returns and in which it exactly fits. Where the urchins are numerous, the rock may be honeycombed by these excavations. Smaller individuals particularly use these retreats, which provide some protection from predators. In lagoons and rock pools, individuals are smaller than they are in the open sea. P. lividus is unable to tolerate low salinity
. After exceptional quantities of rain fell in Corsica
in the autumn of 1993, there was mass mortality of urchins in the Urbini Lagoon. However the urchin is relatively unaffected by organic pollution and heavy metals, in fact it flourishes near sewage
outlets. There are wide swings in population densities over its range, which have not been completely explained.
and release gamete
s into the water column. The larvae form part of the zooplankton
for about 28 days before settling and undergoing metamorphosis.
species and characterised by a low biomass of primary producers with a small number of associated species. Where numbers are low, there tend to be forests of Laminaria
and Cystoseira
and a much richer, three dimensional community. The barren grounds can persist for years though whether this is due to overgrazing by urchins or prevention of recruitment of multicellular photosynthetic organisms by encrusting algae is unclear.
Some juveniles of small fish species shelter among the spines. These include the clingfishes Apletodon incognitus and Lepadogaster candolii and the gobies
, Gobius bucchichi
, Zebrus zebrus and Millerigobius macrocephalus
.
The main predators on P. lividus in the Mediterranean Sea are the spider crab
(Maja crispata), the fish Diplodus sargus
, Diplodus vulgaris, Labrus merula and Coris julis and the gastropod, Hexaplex trunculus
. The spiny starfish (Marthasterias glacialis) is a main predator elsewhere. Predation is dependent on size; juvenile urchins are more vulnerable as their spines are less formidable. In most locations the urchins are nocturnal feeders, but where predators are more active at night the urchins may feed during day instead.
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of sea urchin
Sea urchin
Sea urchins or urchins are small, spiny, globular animals which, with their close kin, such as sand dollars, constitute the class Echinoidea of the echinoderm phylum. They inhabit all oceans. Their shell, or "test", is round and spiny, typically from across. Common colors include black and dull...
in the family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Parechinidae
Parechinidae
Parechinidae is a family of sea urchins in the class Echinoidea.-Characteristics:All Camarodonts have imperforate tubercles and compound ambulacral plates. In addition, the characteristics of the Parechinids include the interambulacral plates being densely covered with tubercles with many subequal...
commonly known as the purple sea urchin. It is the type species
Type species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
of the genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
and occurs in the Mediterranean Sea and eastern Atlantic Ocean.
Description
P. lividus has a circular, flattened greenish testTest (biology)
A test is a term used to refer to the shell of sea urchins, and also the shell of certain microorganisms, such as testate foraminifera and testate amoebae....
with a diameter of up to seven centimetres. The test is densely clothed in long and sharply pointed spines that are usually purple but are occasionally other colours including dark brown, light brown and olive green. There are five or six pairs of pores on each ambulacral
Ambulacral
Ambulacral is a term typically used in the context of anatomical parts of the phylum Echinodermata or class Asteroidea and Edrioasteroidea. Echinoderms can have ambulacral parts that include ossicles, plates, spines, and suckers. For example, sea stars or "star fish" have an ambulacral groove on...
plate. The tube feet
Tube feet
Tube feet are the many small tubular projections found most famously on the oral face of a sea star's arms, but are characteristic of the water vascular system of the echinoderm phylum which also includes sea urchins, sand dollars and sea cucumbers and many other sea creatures.Tube feet function in...
are in groups of 5 or 6, arranged in small arcs.
Distribution
P. lividus is found throughout the Mediterranean SeaMediterranean Sea
The Mediterranean Sea is a sea connected to the Atlantic Ocean surrounded by the Mediterranean region and almost completely enclosed by land: on the north by Anatolia and Europe, on the south by North Africa, and on the east by the Levant...
and in the eastern Atlantic Ocean
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
from western Scotland
Scotland
Scotland is a country that is part of the United Kingdom. Occupying the northern third of the island of Great Britain, it shares a border with England to the south and is bounded by the North Sea to the east, the Atlantic Ocean to the north and west, and the North Channel and Irish Sea to the...
and Ireland
Ireland
Ireland is an island to the northwest of continental Europe. It is the third-largest island in Europe and the twentieth-largest island on Earth...
to the Azores
Azores
The Archipelago of the Azores is composed of nine volcanic islands situated in the middle of the North Atlantic Ocean, and is located about west from Lisbon and about east from the east coast of North America. The islands, and their economic exclusion zone, form the Autonomous Region of the...
, Canary Islands
Canary Islands
The Canary Islands , also known as the Canaries , is a Spanish archipelago located just off the northwest coast of mainland Africa, 100 km west of the border between Morocco and the Western Sahara. The Canaries are a Spanish autonomous community and an outermost region of the European Union...
and Morocco
Morocco
Morocco , officially the Kingdom of Morocco , is a country located in North Africa. It has a population of more than 32 million and an area of 710,850 km², and also primarily administers the disputed region of the Western Sahara...
. It is most common in the western Mediterranean, the coasts of Portugal
Portugal
Portugal , officially the Portuguese Republic is a country situated in southwestern Europe on the Iberian Peninsula. Portugal is the westernmost country of Europe, and is bordered by the Atlantic Ocean to the West and South and by Spain to the North and East. The Atlantic archipelagos of the...
and the Bay of Biscay
Bay of Biscay
The Bay of Biscay is a gulf of the northeast Atlantic Ocean located south of the Celtic Sea. It lies along the western coast of France from Brest south to the Spanish border, and the northern coast of Spain west to Cape Ortegal, and is named in English after the province of Biscay, in the Spanish...
, where the water temperature in winter varies between 10 and 15°C.
Habitat
P. lividus is usually found just below low water mark at depths down to twenty metres and sometimes also in rock poolsTide pool
Tide pools are rocky pools by oceans that are filled with seawater. Many of these pools exist as separate entities only at low tide.Tide pools are habitats of uniquely adaptable animals that have engaged the special attention of naturalists and marine biologists, as well as philosophical...
. It is found on rocks and boulders, and in seagrass
Seagrass
Seagrasses are flowering plants from one of four plant families , all in the order Alismatales , which grow in marine, fully saline environments.-Ecology:...
meadows of Zostera marina
Zostera marina
Zostera marina is a species of seagrass known by the common names common eelgrass and seawrack. It is an aquatic plant native to marine environments on the coastlines of mostly northern sections of North America and Eurasia. It is the most wide-ranging marine flowering plant in the Northern...
and Posidonia oceanica
Posidonia oceanica
Posidonia oceanica is a seagrass species that is endemic to the Mediterranean Sea. It forms large underwater meadows that are an important part of the ecosystem. The fruit is free floating and known in Italy as 'the olive of the sea'...
. Although Cymodocea nodosa
Cymodocea nodosa
Cymodocea nodosa is a species of seagrass in the family Cymodoceaceae and is sometimes known as little Neptune grass. As a seagrass, it is restricted to growing underwater and is found in shallow parts of the Mediterranean Sea and certain adjoining areas of the Atlantic Ocean.-Description:C....
is a preferred food item, it is seldom found in meadows of this seagrass, perhaps because the shifting sand substrate does not suit it or because of pressure from predators
Predation
In ecology, predation describes a biological interaction where a predator feeds on its prey . Predators may or may not kill their prey prior to feeding on them, but the act of predation always results in the death of its prey and the eventual absorption of the prey's tissue through consumption...
. In fact it avoids soft substrates and can sometimes be found clustered on stones or shell "islands" surrounded by sand. In shallow or exposed waters it can use its mouth and spines to dig into soft rocks to create cavities into which it returns and in which it exactly fits. Where the urchins are numerous, the rock may be honeycombed by these excavations. Smaller individuals particularly use these retreats, which provide some protection from predators. In lagoons and rock pools, individuals are smaller than they are in the open sea. P. lividus is unable to tolerate low salinity
Salinity
Salinity is the saltiness or dissolved salt content of a body of water. It is a general term used to describe the levels of different salts such as sodium chloride, magnesium and calcium sulfates, and bicarbonates...
. After exceptional quantities of rain fell in Corsica
Corsica
Corsica is an island in the Mediterranean Sea. It is located west of Italy, southeast of the French mainland, and north of the island of Sardinia....
in the autumn of 1993, there was mass mortality of urchins in the Urbini Lagoon. However the urchin is relatively unaffected by organic pollution and heavy metals, in fact it flourishes near sewage
Sewage
Sewage is water-carried waste, in solution or suspension, that is intended to be removed from a community. Also known as wastewater, it is more than 99% water and is characterized by volume or rate of flow, physical condition, chemical constituents and the bacteriological organisms that it contains...
outlets. There are wide swings in population densities over its range, which have not been completely explained.
Biology
Individual P. lividus are either male or female although hermaphroditism has been observed. They aggregate for spawningSpawn (biology)
Spawn refers to the eggs and sperm released or deposited, usually into water, by aquatic animals. As a verb, spawn refers to the process of releasing the eggs and sperm, also called spawning...
and release gamete
Gamete
A gamete is a cell that fuses with another cell during fertilization in organisms that reproduce sexually...
s into the water column. The larvae form part of the zooplankton
Zooplankton
Zooplankton are heterotrophic plankton. Plankton are organisms drifting in oceans, seas, and bodies of fresh water. The word "zooplankton" is derived from the Greek zoon , meaning "animal", and , meaning "wanderer" or "drifter"...
for about 28 days before settling and undergoing metamorphosis.
Ecology
P. lividus is a browser, eating a range of red, green and brown algae in addition to seagrass. The benthic community is much affected by the number of urchins and their food preferences. Where they are numerous they tend to be surrounded by "barren ground" colonised by encrusting CorallinaceaeCorallinaceae
The Corallinaceae are one of the two extant Coralline families of red algae; they are differentiated from the morphologically similar Sporolithaceae by their formation of grouped sporangial chambers, clustered into sori...
species and characterised by a low biomass of primary producers with a small number of associated species. Where numbers are low, there tend to be forests of Laminaria
Laminaria
Laminaria is a genus of 31 species of brown algae , all sharing the common name "kelp". This economically important genus is characterized by long, leathery laminae and relatively large size. Some species are referred to by the common name Devil's apron, due to their shape, or sea colander, due to...
and Cystoseira
Cystoseira
Cystoseira is a genus of brown algae in the order Fucales.-Description:Cystoseira is characterized by highly differentiated basal and apical regions and the presence of catenate pneumatocysts ....
and a much richer, three dimensional community. The barren grounds can persist for years though whether this is due to overgrazing by urchins or prevention of recruitment of multicellular photosynthetic organisms by encrusting algae is unclear.
Some juveniles of small fish species shelter among the spines. These include the clingfishes Apletodon incognitus and Lepadogaster candolii and the gobies
Goby
The gobies form the family Gobiidae, which is one of the largest families of fish, with more than 2,000 species in more than 200 genera. Most are relatively small, typically less than 10 cm in length...
, Gobius bucchichi
Bucchich's goby
The Bucchich's goby is a coastal fish of the Gobiidae family. Demersal subtropical marine species, up to 10.0 cm maximal length, usually 3.0-3.8 cm. Sexually mature at one year, has 3.4-3.8 cm long.-Range:...
, Zebrus zebrus and Millerigobius macrocephalus
Large-headed Goby
The large-headed goby is a fish species of the family Gobiidae. Its genus Millerigobius is monotypic.The natural range of this fish is coastal waters of the Adriatic Sea and Eastern Mediterranean...
.
The main predators on P. lividus in the Mediterranean Sea are the spider crab
Spider crab
The term spider crab can refer to various species of crab in the family Majidae. See crab spider for spiders of the Thomisidae family.*Japanese spider crab , the largest living species of crab, found on the bottom of the Pacific Ocean*Libinia emarginata, the portly spider crab, a species of crab...
(Maja crispata), the fish Diplodus sargus
Sargo
Sargo is a town in the Kongoussi Department of Bam Province in northern Burkina Faso. It has a population of 1,628.-External links:*...
, Diplodus vulgaris, Labrus merula and Coris julis and the gastropod, Hexaplex trunculus
Hexaplex trunculus
Hexaplex trunculus is a medium-sized species of sea snail, a marine gastropod mollusk in the family Muricidae, the murex shells or rock snails....
. The spiny starfish (Marthasterias glacialis) is a main predator elsewhere. Predation is dependent on size; juvenile urchins are more vulnerable as their spines are less formidable. In most locations the urchins are nocturnal feeders, but where predators are more active at night the urchins may feed during day instead.