Editing Barnacle (section)

== Ecology ==

=== Filter feeding ===

Most barnacles are filter feeders. From within their shell, they repeatedly reach into the water column with their cirri. These feathery appendages beat rhythmically to draw [[plankton]] and detritus into the shell for consumption.<ref name=Doyle1997/><ref>{{cite book |last1=Riisgård |first1=Hans Ulrik |editor1=Thiel, Martin |editor2=Watling, Les |chapter=Filter-feeding mechanisms in crustaceans |title=Life styles and feeding biology. The natural history of the Crustacea |volume=2 |year=2015 |publisher=Oxford University Press |url=https://www.researchgate.net/publication/289520648 |pages=418–463}}</ref>

<gallery class="center" mode="nolines" widths="235" heights="200">
File:Giant Acorn Barnacle, Embarcadero, Morro Bay, CA, US imported from iNaturalist photo 149595197.jpg|''[[Balanus nubilus]]'' with cirri extended
File:Entenmuscheln.jpg|[[Goose barnacle]]s, with their cirri extended for feeding
File:Scalpellid barnacle feeding.jpg|A [[Scalpellidae|scalpellid]] barnacle feeding
File:Semibalanus balanoides upernavik 2007-07-05.ogv|''[[Semibalanus balanoides]]'' filter-feeding by projecting and retracting their cirri 
</gallery>

=== Species-specific zones ===

Although they have been found at water depths to {{convert|600|m|ft|-2|abbr=on}},<ref name=Doyle1997/> most barnacles inhabit shallow waters, with 75% of species living in water depths less than {{convert|100|m|ft|-2|abbr=on}},<ref name=Doyle1997/> and 25% inhabiting the [[intertidal zone]].<ref name=Doyle1997/> Within the intertidal zone, different species of barnacles live in very tightly constrained locations, allowing the exact height of an assemblage above or below sea level to be precisely determined.<ref name=Doyle1997/>

Since the intertidal zone periodically [[Desiccation|desiccates]], barnacles are well adapted against water loss. Their calcite shells are impermeable, and they can close their apertures with movable plates when not feeding.<ref name="Buckeridge 2012">{{cite journal |last=Buckeridge |first=John S. |title=Opportunism and the resilience of barnacles (Cirripedia: Thoracica) to environmental change |journal=Integrative Zoology |volume=7 |issue=2 |date=2012 |issn=1749-4877 |doi=10.1111/j.1749-4877.2012.00286.x |pages=137–146|pmid=22691197 }}</ref> Their hard shells are assumed by zoologists to have evolved as an [[anti-predator adaptation]].<ref name="Zimmer Ferrier Zimmer 2021">{{cite journal |last1=Zimmer |first1=Richard K. |last2=Ferrier |first2=Graham A. |last3=Zimmer |first3=Cheryl Ann |title=Chemosensory Exploitation and Predator-Prey Arms Races |journal=Frontiers in Ecology and Evolution |volume=9 |date=2021-11-12 |issn=2296-701X |doi=10.3389/fevo.2021.752327 |doi-access=free |page=}}</ref>

One group of stalked barnacles has adapted to a rafting lifestyle, drifting around close to the water's surface. They colonize every floating object, such as driftwood, and like some [[Acorn barnacle|non-stalked barnacles]] attach themselves to marine animals. The species most specialized for this lifestyle is ''[[Dosima fascicularis]]'', which secretes a gas-filled cement that makes it float at the surface.<ref>{{Cite journal |last1=Zheden |first1=Vanessa |last2=Kovalev |first2=Alexander |last3=Gorb |first3=Stanislav N. |last4=Klepal |first4=Waltraud |date=2015-02-06 |title=Characterization of cement float buoyancy in the stalked barnacle Dosima fascicularis (Crustacea, Cirripedia) |journal=[[Interface Focus]] |volume=5 |issue=1 |pages=20140060 |doi=10.1098/rsfs.2014.0060 |pmc=4275874 |pmid=25657839}}</ref>

=== Parasitism ===

[[File:Sacculina carcini.jpg|thumb|''[[Sacculina carcini]]'' (highlighted) parasitising the crab ''[[Liocarcinus holsatus]]''. ]]

Other members of the class have an entirely different mode of life. Barnacles of the [[superorder]] [[Rhizocephala]], including the [[genus]] ''[[Sacculina]]'', are [[parasitic castrator]]s of other arthropods, including crabs. The anatomy of these parasitic barnacles is greatly reduced compared to their free-living relatives. They have no carapace or limbs, having only unsegmented sac-like bodies. They feed by extending thread-like rhizomes of living cells into their hosts' bodies from their points of attachment.<ref name="Hosie 2018">{{cite web |url=http://www.marlin.ac.uk/species/detail/2233 |title=Crab hacker barnacle (''Sacculina carcini'') |last=Hosie |first=A. M. |year=2008 |publisher=[[MarLIN]] |access-date=14 January 2018 |url-status=live |archive-url=https://web.archive.org/web/20180115184524/http://www.marlin.ac.uk/species/detail/2233 |archive-date=15 January 2018 }}</ref>
<ref name=IZ/>

Goose barnacles of the genus ''[[Anelasma]]'' (in the order [[Pollicipedomorpha]]) are specialized parasites of certain shark species. Their cirri are no longer used to filter-feed. Instead, these barnacles get their nutrients directly from the host through a root-like body part embedded in the shark's flesh.<ref>{{cite journal |last=Rees |first=David John |date=16 June 2014 |title=On the Origin of a Novel Parasitic-Feeding Mode within Suspension-Feeding Barnacles |journal=Current Biology |volume=24 |issue=12 |pages=1429-1434 |doi=10.1016/j.cub.2014.05.030 |doi-access=free}}</ref>

=== Competitors ===

[[File:CornishBarnacles.JPG|thumb|Barnacles and [[limpet]]s compete for space in the intertidal zone]]

Barnacles are displaced by [[limpet]]s and [[mussel]]s, which compete for space.<ref name=Doyle1997/> They employ two strategies to overwhelm their competitors: "swamping", and fast growth. In the swamping strategy, vast numbers of barnacles settle in the same place at once, covering a large patch of substrate, allowing at least some to survive in the balance of probabilities.<ref name=Doyle1997/> Fast growth allows the suspension feeders to access higher levels of the water column than their competitors, and to be large enough to resist displacement; species employing this response, such as the aptly named ''[[Megabalanus]]'', can reach {{convert|7|cm|in|0|abbr=on}} in length.<ref name=Doyle1997/>

Competitors may include other barnacles. Balanoids gained their advantage over the chthalamoids in the Oligocene, when they evolved tubular skeletons, which provide better anchorage to the substrate, and allow them to grow faster, undercutting, crushing, and smothering chthalamoids.<ref name=Stanley2008>{{cite journal |last=Stanley |first=Steven M. |title=Predation defeats competition on the seafloor |journal=[[Paleobiology (journal)|Paleobiology]] |date=8 April 2016 |volume=34 |issue=1 |pages=1–21 |doi=10.1666/07026.1 |bibcode=2008Pbio...34....1S |s2cid=83713101 }}</ref>

=== Predators and parasites ===

Among the most common [[Predation|predator]]s of barnacles are [[whelk]]s. They are able to grind through the calcareous exoskeleton and eat the animal inside. Barnacle larvae are consumed by filter-feeding [[Benthic zone|benthic]] predators including the [[mussel]] ''Mytilus edulis'' and the [[Ascidiacea|ascidian]] ''Styela gibbsi''.<ref>{{cite journal |last1=Cowden |first1=Cynthia |last2=Young |first2=Craig M. |last3=Chia |first3=F. S. |title=Vol. 14: 145-149. 1984 MARINE ECOLOGY - PROGRESS SERIES Mar. Ecol. h o g . Ser. 1 h b l i s h e d January 2 Differential predation on marine invertebrate larvae by two benthic predators |journal=Marine Ecology - Progress Series |date=1984 |volume=14 |pages=145–149 |doi=10.3354/meps014145 |url=https://www.int-res.com/articles/meps/14/m014p145.pdf}}</ref> Another predator is the starfish species ''[[Pisaster ochraceus]]''.<ref>{{cite journal |last1=Harley |first1=C. D. G. |last2=Pankey |first2=M. S. |last3=Wares |first3=J. P. |last4=Grosberg |first4=R. K. |last5=Wonham |first5=M. J. |s2cid=18549566 |title=Color Polymorphism and Genetic Structure in the Sea Star |journal=[[The Biological Bulletin]] |date=December 2006 |volume=211 |issue=3 |pages=248–262 |doi=10.2307/4134547 |pmid=17179384 |jstor=4134547 }}</ref><ref>{{cite web |last=Holmes |first=Jan |title=Seashore players most successful when they're in their zone  |url=http://www.beachwatchers.wsu.edu/island/essays/zonation.htm |year=2002 |work=WSU Beach Watchers |access-date=March 6, 2010 |archive-url=https://web.archive.org/web/20100621224920/http://beachwatchers.wsu.edu/island/essays/zonation.htm |archive-date=2010-06-21 }}</ref> A stalked barnacle in the Iblomorpha, ''Chaetolepas calcitergum'', lacks a heavily mineralised shell, but contains a high concentration of toxic [[bromine]]; this may serve to deter predators.<ref>{{cite news |last=Walker |first=Matt |title=Barnacles become toxic to repel hungry predators |url=http://news.bbc.co.uk/earth/hi/earth_news/newsid_8426000/8426208.stm |website=[[BBC]] Earth News |date=22 December 2009 |access-date=18 February 2024}}</ref> The [[turbellaria]]n flatworm ''[[Stylochus]]'', a serious predator of [[oyster spat]], has been found in barnacles.<ref name="Arvy Nigrelli 1969"/> Parasites of barnacles include many species of [[Gregarinasina]] ([[alveolate]] protozoa), a few fungi, a few species of [[Trematoda|trematodes]], and a parasitic castrator [[Isopoda|isopod]], ''[[Hemioniscus balani]]''.<ref name="Arvy Nigrelli 1969">{{cite journal |last1=Arvy |first1=Lucie |last2=Nigrelli |first2=Ross F. |title=Studies on the biology of barnacles: parasites of Balanus eburneus and B. balanoides from New York Harbor and a review of the parasites and diseases of other Cirripedia |journal=[[Zoologica]] |date=1969 |volume=54 |issue=3 |pages=95–102 |url=https://www.biodiversitylibrary.org/page/50998597#page/13/mode/1up}}</ref>