Editing Echinoderm (section)

==Ecology==

[[File:Blue Linckia Starfish.JPG|thumb|upright|A blue ''Linckia'' starfish on a [[coral reef]], a biodiverse ecosystem]]

Echinoderms are numerous<!-- and relatively large--> invertebrates whose adults play an important role in benthic [[ecosystem]]s, while the larvae are a major component of the plankton. Among the ecological roles of adults are the grazing of sea urchins, the sediment processing of heart urchins, and the suspension and deposit feeding of crinoids and sea cucumbers.<ref name=Uthicke/><ref>{{harvnb|Brusca|Moore|Shuster|2016|p=968}}</ref> Some sea urchins can bore into solid rock, destabilising rock faces and releasing nutrients into the ocean. Coral reefs are also bored into in this way, but the rate of accretion of carbonate material is often greater than the erosion produced by the sea urchin.<ref>{{harvnb|Herrera-Escalante|López-Pérez|Leyte-Morales|2005}}</ref> Echinoderms sequester about 0.1 gigatonnes of carbon dioxide per year as [[calcium carbonate]], making them important contributors in the global [[carbon cycle]].<ref name="Lebrato Iglesias-Rodríguez 2010">{{harvnb|Lebrato|Iglesias-Rodríguez|Feely|Greeley|2010}}</ref>

Echinoderms sometimes have large population swings which can transform ecosystems. In 1983, for example, the mass mortality of the tropical sea urchin ''[[Diadema antillarum]]'' in the Caribbean caused a change from a coral-dominated reef system to an alga-dominated one.<ref>{{harvnb|Osborne|2000|p=464}}</ref> Sea urchins are among the main herbivores on reefs and there is usually a fine balance between the urchins and the kelp and other algae on which they graze. A diminution of the numbers of predators (otters, lobsters and fish) can result in an increase in urchin numbers, causing [[overgrazing]] of [[kelp forest]]s, resulting in an alga-denuded "[[urchin barren]]".<ref>{{harvnb|Lawrence|1975}}</ref> On the [[Great Barrier Reef]], an unexplained increase in the numbers of [[crown-of-thorns starfish]] (''Acanthaster planci''), which graze on living coral tissue, has greatly increased coral mortality and reduced coral reef [[biodiversity]].<ref>{{harvnb|Birkeland|Lucas|1990}}</ref>