Current estimates place the number of mangrove crab species at 481 in 6 different families, with new species being discovered frequently.[5] Mangrove crabs primarily live in theIndo-West Pacific region inmudflats along tropical coasts.[10] The largest habitats for mangrove crabs are inSoutheast Asia,South America, andNorthern Australia.[9] As their name suggests, they are primarily found amongmangrove tree forests and formsymbiotic relationships with the trees, restricting their habitat to where the trees can grow.[16]
A variety of different species are what makeup the umbrella term of mangrove crabs. The two main crabs that typically dominate mangrove ecosystems are thesesarmid (Grapsidae) andfiddler crabs (Ocypodidae).[6] The main difference between the two crab groups is their foraging habits.[6] Litter ingested by sesarmid crabs forms fragmented organic material that helps stimulate microbial respiration, in contrast fiddler crabs remove reactive organic carbon.[6] Mangrove crabs are a part of theAnimalia kingdom and are put into theArthropoda phylum, Malacostraca class, and Decapoda order.[17] Mangrove crabs can be classified into six different families: Camptandriidae, Dotillidae, Macrophthalmidae, Ocypodidae, Sesarmidae, and Oziidae.[5]
When young, mangrove crabs get most of their nutrients frompolychaete worms and a multitude of microorganisms found living in the sediments and leaves of their environment.[20] As they grow older mangrove crabs are generallydetritivores with their diet consisting of already dead organic material. Mangrove crabs consume a large amount of plant material but are primarily omnivorous.[21] In themangrove swamp this includes dead leaves and corpses of other crustaceans, even that of their own species.[22] In some cases, mangrove crabs may also eat fresh mangrove leaves.[23] Mangrove crabs are predated on by wading birds, fish, sharks,[8] monkeys, hawks, and raccoons.[7] The larvae of mangrove crabs is a major source of food for juvenile fish in waterways near the crabs.[24] Adult mangrove crabs are food for thecrab plover among other protected species.[17] To protect themselves the crabs can climb trees.[25] The only other crustaceans that climb trees arehermit crabs.[26]
Mangrove crabs often construct and inhabit burrows in mangrove sediment. These burrows aid them in enduring the extremes that can be found in mangroves at high and lowtide, allowing them to maintain more constant and ideal temperatures and oxygen levels. These constants can additionally aid othersmall benthic fauna, like polychaetes and juvenile crabs.[27] Mangrove crabs may plug their burrows at intervals determined by theircircadian rhythms,[28] or they may leave them open. The variety in structures and maintenance of these burrows may lead to a variety of different impacts on mangrove sediments, such as increasing or decreasingerodibility.[4] Fiddler crabs generally have very simple 10–40 cm “J-shaped” burrows,[29] while sesarmid crabs that burrow often create complex, branching burrows that can reach over 100 cm in depth.[27] Both types of crab significantly increase the surface area of the sediment and water/air interface to similar extents when scaled for relative abundance.[6] These burrows also result in significant burial and downward travel of mangrove leaves.[30] The burrowing dynamics of mangrove crabs dramatically impacts ecosystems, these dynamics were impacted by bothabiotic factors likesoil composition, andbiotic factors like root depth and tree density.[1]
Depending on its nitrogen content, burial ofdetritus in crab burrows can stimulate microbial growth and activity and lead to variation in mangrove soils’ carbon dioxide efflux,ammonium content, andnitrate content.[6]
Biofilmendosymbiosis occurs on the gills of some mangrove crabs, namelyAratus pisonii andMinuca rapax.[12] Each species of these mangrove crabs likely have distinct bacterial compositions.[12] These microbial biofilms are locations of nitrogen transformation, particularlynitrogen fixation.[36] Bacteria likeCyanobacteria,Alphaproteobacteria,Actinobacteria, andBacteroidota have been found on mangrove crabcarapaces. The biofilms served as a net nitrogen sink and a source of ammonium and dissolved nitrogen to the environment.[36] The importance of the biofilm may be dependent on if the crabs live primarily in burrows or outside burrows. Crabs that live outside burrows may consume their nitrogen frommicrophytobenthos, while crabs that live inside their burrows may rely more on their associated microbes.[37]
Ideal mangrove crab habitats rely heavily on coastal depth andsurface temperature.[9]Climate change due toanthropogenic activities is likely to create fluctuations in these two factors, driving the mangrove crab habitats to higher latitudes.[16] As a result, it is predicted that mangrove habitats will continually shrink for the majority of crab species.[9] This shrinking of habitat space isolates crab communities and shrinksgenetic diversity, making many species more vulnerable to extinction.[16]
Like many other crustaceans, mangrove crabs have historically been caught, prepared and eaten by people all over the world. Crab meat can be prepared simply by boiling the crab either dead or alive until the shell turns from black to red.[38] This practice may be threatened by human activities, however, asmicroplastics have been found to be abundantly common in the gills of mangrove crabs due to human pollution.[14] This not only negatively affects the health of the crabs, but could affect the health of humans who consume them.[14]
Around 6,000 km2 of mangrove wasdeforested between 1996 and 2016, usually redeveloped for fish and shrimpaquaculture, rice cultivation,palm oil plantations,[15] and sometimesurbanization.[39] Diversity of mangrove crabs does not seem to be negatively affected in abandoned aquaculture plots, though logging has significant negative effects on mangrove crabdiversity.[40]
^Luiz Drude de Lacerda (2002).Mangrove ecosystems: function and management. Berlin: Springer-Verlag.ISBN3-540-42208-0.OCLC49238708.
^Tomas Tomascik (1997).The ecology of the Indonesian seas. Oxford: Oxford University Press.ISBN0-19-850186-2.OCLC37594550.
^abBotto, F.; Iribarne, O. (August 2000). "Contrasting Effects of Two Burrowing Crabs (Chasmagnathus granulata andUca uruguayensis) on Sediment Composition and Transport in Estuarine Environments".Estuarine, Coastal and Shelf Science.51 (2):141–151.Bibcode:2000ECSS...51..141B.doi:10.1006/ecss.2000.0642.ISSN0272-7714.
^abcSharifian, Sana; Kamrani, Ehsan; Saeedi, Hanieh (August 2020). "Global biodiversity and biogeography of mangrove crabs: Temperature, the key driver of latitudinal gradients of species richness".Journal of Thermal Biology.92: 102692.doi:10.1016/j.jtherbio.2020.102692.ISSN0306-4565.PMID32888577.S2CID221503106.
^abWarne, Kennedy (2012).Let Them Eat Shrimp : the Tragic Disappearance of the Rainforests of the Sea. Island Press.ISBN978-1-61091-024-8.OCLC974227612.
^abKristensen, Erik; Holmer, Marianne (2001-02-01). "Decomposition of plant materials in marine sediment exposed to different electron acceptors (O2, NO3−, and SO42−), with emphasis on substrate origin, degradation kinetics, and the role of bioturbation".Geochimica et Cosmochimica Acta.65 (3):419–433.Bibcode:2001GeCoA..65..419K.doi:10.1016/S0016-7037(00)00532-9.ISSN0016-7037.
^Erickson, Amy A.; Feller, Ilka C.; Paul, Valerie J.; Kwiatkowski, Lisa M.; Lee, Woody (February 2008). "Selection of an omnivorous diet by the mangrove tree crabAratus pisonii in laboratory experiments".Journal of Sea Research.59 (1–2):59–69.Bibcode:2008JSR....59...59E.doi:10.1016/j.seares.2007.06.007.
^Mohammed, Saleema (2016)."Goniopsis Cruentata (Mangrove Root Crab)"(PDF).The Online Guide to the Animals of Trinidad and Tobago. The University of the West Indies at St. Augustine, Trinidad and Tobago.
^A. I. Robertson; D. M. Alongi (1992).Tropical mangrove ecosystems. Washington, DC: American Geophysical Union.ISBN978-1-118-66508-4.OCLC647036902.
^Peter K. L. Ng; Richard Corlett; Hugh T. W. Tan (2011).Singapore biodiversity : an encyclopedia of the natural environment and sustainable development. Singapore: Editions Didier Millet in association with Raffles Museum of Biodiversity Research.ISBN978-981-4260-08-4.OCLC719429723.
^Kricher, John (2015).A Neotropical Companion: an Introduction to the Animals, Plants, and Ecosystems of the New World Tropics. Illustrated by Andrea S. LeJeune. Princeton: Princeton University Press.ISBN978-1-4008-6691-5.OCLC900344180.
^Lim, Shirley S. L. (2006). "Fiddler Crab Burrow Morphology: How Do Burrow Dimensions and Bioturbative Activities Compare in Sympatric Populations of Uca vocans (Linnaeus, 1758) and U. annulipes (H. Milne Edwards, 1837)?".Crustaceana.79 (5):525–540.doi:10.1163/156854006777584241.ISSN0011-216X.JSTOR20107679.
^Micheli, Fiorenza (1993-10-15). "Feeding ecology of mangrove crabs in North Eastern Australia: mangrove litter consumption bySesarma messa andSesarma smithii".Journal of Experimental Marine Biology and Ecology.171 (2):165–186.doi:10.1016/0022-0981(93)90002-6.ISSN0022-0981.
^Holmer, Marianne; Kristensen, Erik; Banta, Gary; Hansen, Kim; Jensen, Mikael Hjorth; Bussawarit, Nipuvan (1994). "Biogeochemical Cycling of Sulfur and Iron in Sediments of a South-East Asian Mangrove, Phuket Island, Thailand".Biogeochemistry.26 (3):145–161.doi:10.1007/BF00002904.ISSN0168-2563.JSTOR1469192.S2CID97990426.
^Smith, Thomas J.; Boto, Kevin G.; Frusher, Stewart D.; Giddins, Raymond L. (November 1991). "Keystone species and mangrove forest dynamics: the influence of burrowing by crabs on soil nutrient status and forest productivity".Estuarine, Coastal and Shelf Science.33 (5):419–432.Bibcode:1991ECSS...33..419S.doi:10.1016/0272-7714(91)90081-L.
^De Cock, Andrée; Forio, Marie Anne Eurie; De Meulenaer, Bruno; Tack, Filip; Dominguez-Granda, Luis; Goethals, Peter L.M. (2023-02-01). "The nutritional quality of the red mangrove crab (Ucides occidentalis), harvested at two reserves in the Guayas estuary".Food Chemistry.401: 134105.doi:10.1016/j.foodchem.2022.134105.hdl:1854/LU-8766631.ISSN0308-8146.PMID36108382.S2CID252099001.
^Geist, Simon Joscha; Nordhaus, Inga; Hinrichs, Saskia (2012-01-01). "Occurrence of species-rich crab fauna in a human-impacted mangrove forest questions the application of community analysis as an environmental assessment tool".Estuarine, Coastal and Shelf Science.96:69–80.Bibcode:2012ECSS...96...69G.doi:10.1016/j.ecss.2011.10.002.ISSN0272-7714.
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