Editing Sea urchin (section)

=== 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>