# Maerl
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{{short description|Coralline red algae}}
[[File:ARRAN SEASCENES 013.jpg|thumb|Maerl off the coast of the [Isle of Arran](/source/Isle_of_Arran)]]
[[File:Close-up, Coral beach, Isle of Skye.jpg|thumb|Calcified remains of maerl, on the "coral beach" in the [Isle of Skye](/source/Isle_of_Skye)]]
[[File:Maërl.JPG|thumb|Maerl in [Lanildut](/source/Lanildut).]]
thumb|Pieces of popcorn-like maerl from Fuerteventura island.
'''Maerl''' (also [rhodolith](/source/rhodolith)) is a collective name for non-[geniculate](/source/geniculate_(alga)) [coralline](/source/Coralline_algae) [red algae](/source/red_algae) with a certain growth habit.[{{Cite journal | doi = 10.1146/annurev.es.17.110186.001421 | jstor = 2096997 | last1 = Steneck | first1 = R. S. | title = The Ecology of Coralline Algal Crusts: Convergent Patterns and Adaptative Strategies | journal = Annual Review of Ecology and Systematics | volume = 17 | pages = 273–303 | year = 1986 }}] Maerl grows at a rate of c. 1 mm per year.[{{cite journal | last1 = Blake | first1 = C. | last2 = Maggs | first2 = C.A. | year = 2003 | title = Comparative growth rates and internal banding periodicity of maerl species (Corallinales, Rhodophyta) from northern Europe | journal = Phycologia | volume = 42 | issue = 6| pages = 606–612 | doi=10.2216/i0031-8884-42-6-606.1| bibcode = 2003Phyco..42..606B | s2cid = 83523566 }}] It accumulates as unattached particles and forms extensive beds in suitable sublittoral sites.[Vize, S.; Blake, C.; Hinojosa, G. and Maggs, C.A. 2003. The distribution and composition of maerl beds in Northern Ireland. ''PMNHS Newsletter'' No.13 p.26] The term maerl originally refers to the branched growth form of Lemoine (1910)[{{Cite journal|last=Lemoine|title=Répartition et mode de vie du maërl ( Lithothamnium calcareum) aux environs de Concarneau (Finistère).|journal=Annales de l'Institut Océanographique|date=1910|volume=1|pages=1–29}}] and ''rhodolith'' is a sedimentological or genetic term for both the nodular and branched growth forms (Basso et al., 2015).[{{Cite journal|last=Basso|date=2015|title=Monitoring deep Mediterranean rhodolith beds|journal=Aquatic Conservation: Marine and Freshwater Ecosystems|volume=26|issue=3|doi=10.1002/aqc.2586|pages=549–561|url=https://arts.units.it/bitstream/11368/2849200/8/Monitoring%20deep%20Mediterranean%20rhodolith%20beds.pdf|doi-access=free|archive-date=2022-11-14|access-date=2018-09-16|archive-url=https://web.archive.org/web/20221114162226/https://arts.units.it/bitstream/11368/2849200/8/Monitoring%20deep%20Mediterranean%20rhodolith%20beds.pdf|url-status=dead}}] The terms rhodolith and maerl are used in very similar ways. A study in 2023 clarifies that maerl refers to only living, branched coralline thalli, while rhodolith includes unattached coralline red algae, both dead and alive.[{{Cite journal |last1=Costa |first1=Dimítri de Araújo |last2=Dolbeth |first2=Marina |last3=Christoffersen |first3=Martin Lindsey |last4=Zúñiga-Upegui |first4=Pamela Tatiana |last5=Venâncio |first5=Márcia |last6=de Lucena |first6=Reinaldo Farias Paiva |date=2023-07-11 |title=An Overview of Rhodoliths: Ecological Importance and Conservation Emergency |journal=Life |language=en |volume=13 |issue=7 |pages=1556 |doi=10.3390/life13071556 |doi-access=free |issn=2075-1729 |pmc=10382044 |pmid=37511931|bibcode=2023Life...13.1556C }}]
==Description==
In Europe maerl beds occur throughout the Mediterranean, along most of the Atlantic coast from Portugal to Norway, and in the English Channel, Irish Sea and North Sea.[Grall, J., Le Loc'h, F., Guyonnet, B., and Riera, P. (2006) "Community structure and food web based on stable isotopes (δ15N and δ13C) analysis of a North Eastern Atlantic maerl bed". ''Journal of Experimental Marine Biology and Ecology'' 338, 1–15 [Online] Available at: http://horizon.documentation.ird.fr/exl-doc/vcc/2006/11/010037649.pdf{{dead link|date=January 2018 |bot=InternetArchiveBot |fix-attempted=yes }}] The distribution of maerl is dependent on water movement, light and salinity concentration.[Wilson, S., Blake, C., Berges, J.A., and Maggs, C.A. (2004) "Environmental tolerances of free-living coralline algae (maerl): implications for European marine conservation". ''Journal of Biological Conservation'' 120, 279–289. [Online] Available at: http://www.qub.ac.uk/bb-old/provan/pdf/charmaine2.pdf] Maerl beds occur in the [photic zone](/source/photic_zone), and can be found to around 30 m depth in the British Isles and up to 120 m deep in the Mediterranean.[{{cite journal | last1 = Hall-Spencer | first1 = JM. | last2 = Moore | first2 = PG. | year = 2000 | title = Scallop dredging has profound, long-term impacts on maerl habitats | url =https://pearl.plymouth.ac.uk/bitstream/10026.1/1362/2/Hall-Spencer%20Moore%20ICES%20J.%20Mar.%20Sci.%202000.pdf | journal = ICES Journal of Marine Science | volume = 57 | issue = 5| pages = 1407–1415 | doi=10.1006/jmsc.2000.0918| doi-access = free | bibcode = 2000ICJMS..57.1407H }}] Maerl deposits can reach up to 10 m thick, but are usually much thinner; carbon dating has shown that they can be more than 5500 years old.[Grall, J. and Hall-Spencer, J.M. (2003) Problems facing maerl conservation in Brittany. ''Aquatic Conservation: Marine and Freshwater Ecosystems'' 13, 55–64. [Online] Available at: http://www.ukmpas.org/pdf/Grall_Hall-Spencer_2003.pdf {{Webarchive|url=https://web.archive.org/web/20150617164352/http://www.ukmpas.org/pdf/Grall_Hall-Spencer_2003.pdf |date=2015-06-17 }}]
In the [British Isles](/source/British_Isles) maerl is composed of three species of [coralline algae](/source/coralline_algae) growing loose in beds of fragmented nodules in the sub-littoral. The species generally involved are: ''[Lithothamnion corallioides](/source/Lithothamnion_corallioides)'',[[http://www.algaebase.org/speciesdetail.lasso?species_id=110&sk=0&from=results&-session=abv3:51909EC30a4171DDE6xoK2749EAB Algaebase]] ''[Lithothamnion glaciale](/source/Lithothamnion_glaciale)'' and ''[Phymatolithon](/source/Phymatolithon) calcareum''.[Irvine, L.M and Chamberlain, Y.M. 1994. ''Seaweeds of the British Isles.'' Volume ''1'', Part 2B. The Natural History Museum, London. {{ISBN|0-11-310016-7}}][{{Cite web |url=http://www.algaebase.org/CommonDetail.lasso?cname_id=583&sk=0&-session=abv3:51909EC30a4171DDE6xoK2749EAB |title=Algaebase |access-date=2007-04-20 |archive-date=2021-12-04 |archive-url=https://web.archive.org/web/20211204220025/https://www.algaebase.org/CommonDetail.lasso?cname_id=583&sk=0&-session=abv3:51909EC30a4171DDE6xoK2749EAB |url-status=dead }}]
Maerl is dredged from the sea floor and crushed to form a powder. It is still harvested around the coasts of [Brittany](/source/Brittany) in [France](/source/France) and [Bantry Bay](/source/Bantry_Bay), [Ireland](/source/Ireland), and is a popular fertilizer for [organic gardening](/source/organic_gardening). It was also dredged off [Falmouth, Cornwall](/source/Falmouth%2C_Cornwall), but this ceased in 2004.
Scientists investigated Falmouth maerl and found that ''L. corallioides'' predominated down to 6 m and ''P. calcareum'' from 6–10 m.[{{Citation |last1=Blunden |first1=G. |title=THE COMPOSITION OF MAȄRL BEDS OF ECONOMIC INTEREST IN NORTHERN BRITTANY, CORNWALL AND IRELAND |date=1981-12-31 |work=International Seaweed Symposium (Xth) |pages=651–656 |editor-last=Levrig |editor-first=Tore |url=https://www.degruyter.com/document/doi/10.1515/9783110865271-088/html |access-date=2024-10-15 |place=Berlin, Boston |publisher=De Gruyter |doi=10.1515/9783110865271-088 |isbn=978-3-11-086527-1 |last2=Farnham |first2=W.F. |last3=Jephson |first3=N. |last4=Barwell |first4=C.J. |last5=Fenn |first5=R.H. |last6=Plunkett |first6=B.A.|url-access=subscription }}][{{cite journal | last1 = Blunden | first1 = G | last2 = Campbell | first2 = S A | last3 = Smith | first3 = J R | last4 = Guiry | first4 = M D | last5 = Hession | first5 = C C | last6 = Griffin | first6 = R L | year = 1997 | title = Chemical and physical characterization of calcified red algal deposits known as maërl | journal = J. Applied. Phycol | volume = 9 | issue = 1 | pages = 11–17 | doi = 10.1023/A:1007965325442 | bibcode = 1997JAPco...9...11B | s2cid = 43607799 }}] A 2024 survey by researchers from the [University of Exeter](/source/University_of_Exeter), commissioned by Cornwall Council's Blue Natural Capital Project, found that the [Fal and Helford](/source/Fal_and_Helford) Estuary Special Area of Conservation supports an 880 hectare bed of maerl.[{{Cite web |title=Blue Carbon |url=https://letstalk.cornwall.gov.uk/bluecarbon |access-date=2024-03-07 |website=Let's Talk Cornwall |language=en}}][{{Cite web |last=Morrison |first=Alex |date=2024-03-04 |title=Giant ancient seaweed bed helping in the fight against climate change |url=https://news.exeter.ac.uk/faculty-of-environment-science-and-economy/giant-ancient-seaweed-bed-helping-in-the-fight-against-climate-change/ |access-date=2024-03-07 |website=News |language=en-US}}][{{Cite news |date=2024-03-02 |title=Cornwall researchers discover huge ancient seaweed bed |url=https://www.bbc.com/news/uk-england-cornwall-68450750 |access-date=2024-03-07 |language=en-GB}}]
alt=Maerl Fragments, Maerl Beach, Carraroe, County Galway Ireland|thumb|Maerl fragments, Trá an Doilin, Maerl Beach (incorrectly known as "Coral Strand") Carraroe, County Galway, Ireland
Chemical analysis of maerl showed that it contained 32.1% [CaCO3](/source/Calcium_carbonate) and 3.1% MgCO3 (dry weight).
== Ecology ==
The ecology of maerl habitats has received very little attention in contrast to other marine ecosystems such as [kelp forest](/source/kelp_forest)s or [sea grass](/source/sea_grass) beds.[{{cite journal | last1 = Nelson | first1 = W | year = 2009 | title = Calcified macroalgae – critical to coastal ecosystems and vulnerable to change: a review | journal = Journal of Marine and Freshwater Research | volume = 60 | issue = 8| pages = 187–801 | doi = 10.1071/MF08335 }}] Maerl beds provide a complex habitat for a wide range of [taxa](/source/taxa)[Steller, D.L., Riosmena-Rodríguez, R., Foster, M.S., Roberts, C.A. (2003). "Rhodolith bed diversity in the Gulf of California: the importance of rhodolith structure and consequences of disturbance". ''Aquatic Conservation: Marine Freshwater Ecosystem'' 13, 5–20. [Online] Available at: http://onlinelibrary.wiley.com/doi/10.1002/aqc.564/pdf] with a variety of niches that support high associated invertebrate and algal biodiversity.[{{cite journal | last1 = Kamenos | first1 = N. A. | last2 = Moore | first2 = P.G. | last3 = Hall-Spencer | first3 = J.M. | year = 2004a | title = Nursery-area function of maerl grounds for juvenile queen scallops Aequipecten opercularis and other invertebrates | journal = Marine Ecology Progress Series| volume = 274 | pages = 183–189 | doi=10.3354/meps274183| bibcode = 2004MEPS..274..183K | doi-access = free | hdl = 10026.1/1354 | hdl-access = free }}] and juvenile [scallops](/source/scallops) ''[Aequipecten opercularis](/source/Aequipecten_opercularis)''.[Kamenos, N. A., Moore, P.G., Hall-Spencer, J.M. (2004b) Small-scale distribution of juvenile gadoids in shallow inshore waters; what role does maerl play? ''ICES Journal of Marine Science'' 61, 442–429. [Online] Available at: http://icesjms.oxfordjournals.org/content/61/3/422.short] Maerl beds offer physical refuge and protection from predation as well as productive feeding grounds but are easily damaged by dredging and towed fishing gear.[{{Cite journal | last1=Wilson |first1=S. | first2=C. |last2=Blake |first3=J. A. |last3=Berges |first4=C. A. |last4=Maggs | title=Environmental tolerances of free-living coralline algae (maerl): implications for European marine conservation | journal = [Biological Conservation](/source/Biological_Conservation_(journal)) | volume = 120 |issue=2 | pages = 279–289 | date = November 2004 | doi = 10.1016/j.biocon.2004.03.001 |bibcode=2004BCons.120..279W }}]
==History==
Maerl has been extracted for centuries mainly for use as an agricultural fertilizer. The amount extracted increased in the late 20th century and in 2000, maerl was extracted at c. 5,000 tonnes per year in Ireland and c. 500,000 tonnes per year in France.[{{cite journal | last1 = Grall | first1 = J. | last2 = Hall-Spencer | first2 = J.M. | year = 2003 | title = Problems facing maerl conservation in Brittany | url = http://www.ukmpas.org/pdf/Grall_Hall-Spencer_2003.pdf | journal = Aquatic Conservation: Marine and Freshwater Ecosystems | volume = 13 | issue = S1 | pages = 55–64 | doi = 10.1002/aqc.568 | bibcode = 2003ACMFE..13S..55G | hdl = 10026.1/1359 | s2cid = 53335266 | access-date = 2012-10-15 | archive-date = 2015-06-17 | archive-url = https://web.archive.org/web/20150617164352/http://www.ukmpas.org/pdf/Grall_Hall-Spencer_2003.pdf | url-status = dead }}] In Cornwall, England, maerl has been extracted since the 1970s, but was banned in 2005 by Falmouth Harbour Commissioners.[{{cite journal | last1 = Hall-Spencer | first1 = J.M. | year = 2005 | title = Ban on maerl extraction | doi = 10.1016/j.marpolbul.2005.01.013 | journal = Marine Pollution Bulletin | volume = 50 | issue = 2| page = 121 }}]
An early reference to maerl was made by [John Ray](/source/John_Ray) in 1690 who reported it from Falmouth. In Ireland, maerl is extracted from subfossil beds in Bantry Bay by Celtic Sea Minerals.[[http://www.celticseaminerals.com Celtic Sea Minerals website]] The maerl-forming species ''Lithothamion corallioides'' and ''Phymatolithon calcareum'' are listed in Annex V of the EC Habitats Directive.[[http://www.forest-trends.org/biodiversityoffsetprogram/BBop%20library%202/Europe/Not%20Printed/Council%20Directive%201992%20NATURAL%20HABITATS%20Annex%20V.pdf Forest Trends] {{webarchive|url=https://web.archive.org/web/20080907112019/http://www.forest-trends.org/biodiversityoffsetprogram/BBop%20library%202/Europe/Not%20Printed/Council%20Directive%201992%20NATURAL%20HABITATS%20Annex%20V.pdf |date=2008-09-07 }}]
==Uses==
Used as a soil conditioner, it is dredged from the sea floor and crushed to a powder.[Thomas, D. 2002. ''Seaweeds.'' Life Series. The Natural History Museum, London {{ISBN|0-565-09175-1}}]
The slow growth of individual nodules and their accumulation in beds over a millennial timescale means that there is no possibility of maerl keeping up with dredging for this purpose. Maerl should be considered as a [non-renewable resource](/source/non-renewable_resource), and readily available alternative products (e.g., garden lime) make modern day exploitation controversial.[{{Cite web |last=Divernet |date=2016-12-19 |title=MMO ignores Cornwall dredge campaigners |url=https://divernet.com/scuba-diving/mmo-ignores-cornwall-dredge-campaigners/ |access-date=2024-03-07 |website=divernet.com |language=en-GB}}][{{Cite web |title=Maerl Beds |url=https://www.ospar.org/work-areas/bdc/species-habitats/list-of-threatened-declining-species-habitats/habitats/maerl-beds |access-date=2024-03-07 |website=OSPAR Commission |language=en-gb}}][{{Cite journal |last1=Verma |first1=Audrey |last2=van der Wal |first2=René |last3=Fischer |first3=Anke |date=2017-10-01 |title=New Technological Interventions in Conservation Conflicts: Countering Emotions and Contested Knowledge |url=https://doi.org/10.1007/s10745-017-9936-z |journal=Human Ecology |language=en |volume=45 |issue=5 |pages=683–695 |doi=10.1007/s10745-017-9936-z |issn=1572-9915 |pmc=5680367 |pmid=29170591|bibcode=2017HumEc..45..683V }}]
==References==
Category:Corallinales
Category:Environment of Cornwall
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Adapted from the Wikipedia article [Maerl](https://en.wikipedia.org/wiki/Maerl) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Maerl?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.