Editing Sea urchin (section)

== Ecology ==

=== Trophic level ===
[[File:Sea Urchin.theora.ogv|thumb|Sea urchin in natural habitat]]

Sea urchins feed mainly on [[algae]], so they are primarily [[herbivore]]s, but can feed on sea cucumbers and a wide range of invertebrates, such as [[mussel]]s, [[polychaete]]s, [[sponge]]s, brittle stars, and crinoids, making them omnivores, consumers at a range of [[trophic level]]s.<ref>{{cite journal |last1=Baumiller |first1=Tomasz K. |title=Crinoid Ecological Morphology |journal=Annual Review of Earth and Planetary Sciences |volume=36 |pages=221–49 |year=2008 |doi=10.1146/annurev.earth.36.031207.124116 |bibcode=2008AREPS..36..221B}}</ref>

=== Predators, parasites, and diseases ===
Mass mortality of sea urchins was first reported in the 1970s, but diseases in sea urchins had been little studied before the advent of aquaculture. In 1981, bacterial "spotting disease" caused almost complete mortality in juvenile ''[[Pseudocentrotus depressus]]'' and ''[[Hemicentrotus pulcherrimus]]'', both cultivated in Japan; the disease recurred in succeeding years. It was divided into a cool-water "spring" disease and a hot-water "summer" form.<ref name=Lawrence>{{cite book |author=Lawrence, John M. |title=Edible Sea Urchins: Biology and Ecology |url=https://books.google.com/books?id=6T2JomruARoC |year=2006 |publisher=Elsevier |isbn=978-0-08-046558-6 |pages=167–168}}</ref> Another condition,  [[bald sea urchin disease]], causes loss of spines and skin lesions and is believed to be bacterial in origin.<ref>{{cite journal |title=Diseases of Echinodermata. I. Agents microorganisms and protistans |journal=Diseases of Aquatic Organisms |volume=2 |year=1987 |author=Jangoux, Michel |pages=147–162 |doi=10.3354/dao002147|doi-access=free }}</ref>

Adult sea urchins are usually well protected against most predators by their strong and sharp spines, which can be venomous in some species.<ref name="Defence – spines">{{cite web |url=http://www.nhm.ac.uk/research-curation/research/projects/echinoid-directory/intro/defence1.html |title=Defence – spines |website=Echinoid Directory |publisher=[[Natural History Museum, London|Natural History Museum]] }}</ref> The small [[Diademichthys lineatus|urchin clingfish]] lives among the spines of urchins such as ''[[Diadema (sea urchin)|Diadema]]''; juveniles feed on the pedicellariae and sphaeridia, adult males choose the tube feet and adult females move away to feed on shrimp eggs and molluscs.<ref>{{cite journal |author= Sakashita, Hiroko |year=1992 |title=Sexual dimorphism and food habits of the clingfish, ''Diademichthys lineatus'', and its dependence on host sea urchin |journal=Environmental Biology of Fishes |volume=34 |issue=1 |pages=95–101 |doi=10.1007/BF00004787 |bibcode=1992EnvBF..34...95S |s2cid=32656986 }}</ref>

Sea urchins are one of the favourite foods of many [[lobster]]s, [[crab]]s, [[triggerfish]], [[California sheephead]], [[sea otter]] and [[Anarhichadidae|wolf eels]] (which specialise in sea urchins). All these animals carry particular adaptations (teeth, pincers, claws) and a strength that allow them to overcome the excellent protective features of sea urchins. Left unchecked by predators, urchins devastate their environments, creating what biologists call an [[urchin barren]], devoid of macroalgae and associated [[fauna]].<ref>{{cite book|author1=Terborgh, John|author2=Estes, James A |title=Trophic Cascades: Predators, Prey, and the Changing Dynamics of Nature|url=https://books.google.com/books?id=tjOT8KJ6mF8C&pg=PA38 |year=2013|publisher=Island Press |isbn=978-1-59726-819-6 |pages=38}}</ref> Sea urchins graze on the lower stems of kelp, causing the kelp to drift away and die. Loss of the habitat and nutrients provided by [[kelp forest]]s leads to profound [[Cascade effect (ecology)|cascade effects]] on the marine ecosystem. Sea otters have re-entered [[British Columbia]], dramatically improving coastal ecosystem health.<ref name=dfo>{{cite web |url=http://www.dfo-mpo.gc.ca/species-especes/species/species_seaOtter_e.asp |archive-url=https://web.archive.org/web/20080123224702/http://www.dfo-mpo.gc.ca/species-especes/species/species_seaOtter_e.asp |archive-date=2008-01-23|title=Aquatic Species at Risk – Species Profile – Sea Otter |publisher=[[Fisheries and Oceans Canada]] |access-date=2007-11-29}}</ref>

<gallery style="text-align:center;" mode="packed">
File:Wolf eel eating a sea urchin.jpg|[[Wolf eel]], a highly specialized predator of sea urchins
File:Sea otter with sea urchin.jpg|A [[sea otter]] feeding on a [[Strongylocentrotus purpuratus|purple sea urchin]].
File:Carpilius convexus is consuming Heterocentrotus trigonarius in Hawaii.jpg|A marbled stone crab (''[[Carpilius convexus]]'') attacking a slate pencil sea urchin (''[[Heterocentrotus mamillatus]]'')
File:Saddle Wrasse are feeding on sea urchin in Kona.jpg|A [[Thalassoma duperrey|wrasse]] finishing the remains of a damaged ''[[Tripneustes gratilla]]''
</gallery>

=== Anti-predator defences ===
[[File:Flower urchin by Vincent C Chen.jpg|thumb|The [[flower urchin]] is a dangerous, potentially lethally venomous species.]]

The [[spine (zoology)|spines]], long and sharp in some species, protect the urchin from [[predator]]s. Some tropical sea urchins like [[Diadematidae]], [[Echinothuriidae]] and [[Toxopneustidae]] have venomous spines. Other creatures also make use of these defences; crabs, shrimps and other organisms shelter among the spines, and often adopt the colouring of their host. Some crabs in the [[Dorippidae]] family carry sea urchins, starfish, sharp shells or other protective objects in their claws.<ref name=Thiel>{{cite book|author1=Thiel, Martin|author2=Watling, Les|title=Lifestyles and Feeding Biology |url=https://books.google.com/books?id=RZ-eBgAAQBAJ&pg=PA200 |year=2015 |publisher=Oxford University Press |isbn=978-0-19-979702-8 |pages=200–202}}</ref>

[[Pedicellaria]]e<ref>{{cite web |url=http://www.nhm.ac.uk/research-curation/research/projects/echinoid-directory/intro/defence3.html |title=Defence – pedicellariae |author=<!--Staff writer(s); no by-line.--> |website=Echinoid Directory |publisher=[[Natural History Museum, London|Natural History Museum]] |access-date=2014-08-04 |archive-date=2014-10-06 |archive-url=https://web.archive.org/web/20141006072057/http://www.nhm.ac.uk/research-curation/research/projects/echinoid-directory/intro/defence3.html |url-status=live }}</ref> are a good means of defense against ectoparasites, but not a panacea as some of them actually feed on it.<ref>Hiroko Sakashita, " Sexual dimorphism and food habits of the clingfish, Diademichthys lineatus, and its dependence on host sea urchin ", Environmental Biology of Fishes, vol. 34, no 1, 1994, p. 95–101</ref> The hemal system defends against endoparasites.<ref>{{cite journal |url=https://link.springer.com/content/pdf/10.1007%252FBF01989305.pdf |title=Diseases of echinoderms |journal=Helgoländer Meeresuntersuchungen |volume=37 |issue=1–4 |pages=207–216 |author=Jangoux, M. |year=1984 |access-date=23 March 2018 |bibcode=1984HM.....37..207J |doi=10.1007/BF01989305 |s2cid=21863649 |doi-access=free |archive-date=29 October 2020 |archive-url=https://web.archive.org/web/20201029002716/https://link.springer.com/content/pdf/10.1007%252FBF01989305.pdf |url-status=live }}</ref>

=== Range and habitat ===
Sea urchins are established in most seabed habitats from the intertidal downwards, at an extremely wide range of depths.<ref name="Kroh2010">{{cite journal |last=Kroh |first=Andreas |date=2010 |title=The phylogeny and classification of post-Palaeozoic echinoids |journal=Journal of Systematic Palaeontology |volume=8 |issue=2 |pages=147–212 |doi= 10.1080/14772011003603556|doi-access=free |bibcode=2010JSPal...8..147K }}.</ref> Some species, such as ''[[Cidaris]] abyssicola'', can live at depths of several kilometres. Many genera are found in only the [[abyssal zone]], including many [[cidaroida|cidaroids]], most of the genera in the [[Echinothuriidae]] family, and the "cactus urchins" ''[[Dermechinus]]''. One of the deepest-living families is the [[Pourtalesiidae]],<ref name="Pourtalesiidae">{{cite web |url=http://echinoblog.blogspot.fr/search?q=pourtalesiid |title=Sizes and Species in the Strangest of the Strange : Deep-Sea Pourtalesiid Urchins |last1=Mah |first1=Christopher |date=April 12, 2011 |website=The Echinoblog }}.</ref> strange bottle-shaped irregular sea urchins that live in only the [[hadal zone]] and have been collected as deep as 6850 metres beneath the surface in the [[Sunda Trench]].<ref name="MahDeepest">{{cite web |url=http://echinoblog.blogspot.fr/2014/04/what-are-deepest-known-echinoderms.html |title=What are the Deepest known echinoderms? |last=Mah |first=Christopher |date=8 April 2014 |website=The Echinoblog |access-date=22 March 2018 |archive-date=16 May 2018 |archive-url=https://web.archive.org/web/20180516111356/http://echinoblog.blogspot.fr/2014/04/what-are-deepest-known-echinoderms.html |url-status=live }}.</ref> Nevertheless, this makes sea urchin the class of echinoderms living the least deep, compared to [[brittle star]]s, [[starfish]] and [[crinoid]]s that remain abundant below {{convert|8000|m|ft|-1|abbr=on}} and [[sea cucumber]]s which have been recorded from {{convert|10687|m|ft|-2|abbr=on}}.<ref name="MahDeepest"/>

Population densities vary by habitat, with more dense populations in barren areas as compared to [[kelp]] stands.<ref name=Mattison1977>{{cite journal |author1=Mattison, J.E. |author2=Trent, J.D. |author3=Shanks, AL |author4=Akin, T.B. |author5=Pearse, J.S. |title=Movement and feeding activity of red sea urchins (''Strongylocentrotus franciscanus'') adjacent to a kelp forest |journal=Marine Biology |volume=39 |pages=25–30 |year=1977 |doi=10.1007/BF00395589 |issue=1|bibcode=1977MarBi..39...25M |s2cid=84338735 }}</ref><ref name=Konar2000>{{Cite conference |last=Konar |first=Brenda |author-link=Brenda Konar |title=Habitat Influences on Sea Urchin Populations |editor1-last=Hallock |editor1-first=Pamela |editor2-last=French |editor2-first=Llyn |date=January 2000 |book-title=Diving for Science: Proceedings of the 20th Annual Scientific Diving Symposium, 11–15 October 2000 |url=http://archive.rubicon-foundation.org/8990 |archive-url=https://archive.today/20130415211125/http://archive.rubicon-foundation.org/8990 |url-status=dead |archive-date=April 15, 2013 |location=St. Pete Beach, Florida |publication-place=Nahant, MA |publisher=American Academy of Underwater Sciences |oclc=45371343 |access-date=7 January 2011}}</ref> Even in these barren areas, greatest densities are found in shallow water. Populations are generally found in deeper water if wave action is present.<ref name=Konar2000 /> Densities decrease in winter when storms cause them to seek protection in cracks and around larger underwater structures.<ref name=Konar2000 /> The [[shingle urchin]] (''Colobocentrotus atratus''), which lives on exposed shorelines, is particularly resistant to wave action. It is one of the few sea urchin that can survive many hours out of water.<ref>{{cite web |url=http://echinoblog.blogspot.com/2008/04/holding-on-in-rough-world.html |title=The Echinoblog |author=ChrisM |work=echinoblog.blogspot.com |date=2008-04-21 |access-date=2011-04-01 |archive-date=2024-08-25 |archive-url=https://web.archive.org/web/20240825043204/http://echinoblog.blogspot.com/2008/04/holding-on-in-rough-world.html |url-status=live }}</ref>

Sea urchins can be found in all climates, from warm seas to polar oceans.<ref name="Kroh2010" /> The larvae of the polar sea urchin ''[[Sterechinus neumayeri]]'' have been found to use energy in metabolic processes twenty-five times more efficiently than do most other organisms.<ref name=UD>[https://www.sciencedaily.com/releases/2001/03/010309080313.htm Antarctic Sea Urchin Shows Amazing Energy-Efficiency in Nature's Deep Freeze 15 March 2001] {{Webarchive|url=https://web.archive.org/web/20180322204623/https://www.sciencedaily.com/releases/2001/03/010309080313.htm |date=22 March 2018 }} University of Delaware. Retrieved 22 March 2018</ref> Despite their presence in nearly all the marine ecosystems, most species are found on temperate and tropical coasts, between the surface and some tens of meters deep, close to [[photosynthetic]] food sources.<ref name="Kroh2010"/>

<gallery style="text-align:center;" mode="packed">
File:Sea urchins in california tide pools.jpg|[[Strongylocentrotus purpuratus|Purple sea urchins]] at low tide in [[California]]. They dig a cavity in the rock to hide from predators during the day.
File:Expl1825 - Flickr - NOAA Photo Library.jpg|''[[Dermechinus horridus]]'', an abyssal species, at thousands of meters deep
File:Underwater mcmurdo sound.jpg|Antarctic sea urchin (''[[Sterechinus neumayeri]]'') inhabits frozen seas.
File:Colobocentrotus atratus Shingle urchin.jpg|The shape of the [[shingle urchin]] allows it to stay on wave-beaten cliffs.
</gallery>