Mangrove crab

A variety of different species are what makeup the umbrella term of mangrove crabs. The two main crabs that typically dominate mangrove ecosystems are the sesarmid (Grapsidae) and fiddler 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 the Animalia kingdom and are put into the Arthropoda phylum, Malacostraca class, and Decapoda order.^[17] Mangrove crabs can be classified into six different families: Camptandriidae, Dotillidae, Macrophthalmidae, Ocypodidae, Sesarmidae, and Oziidae.^[5]

Types of mangrove crabs

• Sesarmid crabs
• Fiddler crabs
• Aratus pisonii, Americas
• Haberma, genus of small mangrove crabs, Indo-Pacific, including:
  • Haberma tingkok, Hong Kong
• Metopograpsus messor, Indo-Pacific
• Metopograpsus thukuhar, Indo-Pacific
• Neosarmatium meinerti, Indo-Pacific^[18]
• Neosarmatium smithi, Indo-Pacific^[19]
• Parasesarma leptosoma, western Indian Ocean
• Perisesarma, genus with 23 species, primarily Indo-Pacific, with two West African species, including:
  • Perisesarma bidens, Indo-Pacific
  • Perisesarma guttatum, western Indian Ocean
• Scylla serrata, Indo-Pacific
• Scylla tranquebarica, Indo-Pacific
• Sesarma, genus with close to 20 species, many of which live in mangroves, Americas, Indo-Pacific
• Ucides cordatus, western Atlantic Ocean

Ecology and biogeochemistry

Diet and predators

When young, mangrove crabs get most of their nutrients from

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 low

Mangrove crabs modify particle size, nutrient availability, particle distribution, redox reactions, and organic matter.^[6] Aeration allows for additional microbial decomposition,^[13] oxidation of iron, and reduction of sulfur by anaerobic microbes. This leads to extremely high pyrite concentrations in mangrove soils,^[31] and removal of sulfides that negatively impact plant growth.^[16][32] Surface soils are similarly impacted when mixed by mangrove crab legs.^[33]

Depending on its nitrogen content, burial of detritus in crab burrows can stimulate microbial growth and activity and lead to variation in mangrove soils’ carbon dioxide efflux, ammonium content, and nitrate content.^[6]

The feces of mangrove crabs may help form a

Biofilm endosymbiosis occurs on the gills of some mangrove crabs, namely Aratus pisonii and Minuca rapax.^[12] Each species of these mangrove crabs likely have distinct bacterial compositions.^[12] These microbial biofilms are locations of nitrogen transformation, particularly nitrogen fixation.^[36] Bacteria like Cyanobacteria, Alphaproteobacteria, Actinobacteria, and Bacteroidota have been found on mangrove crab carapaces. 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 from microphytobenthos, while crabs that live inside their burrows may rely more on their associated microbes.^[37]

Human impacts

Climate change

Ideal mangrove crab habitats rely heavily on coastal depth and

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, as microplastics 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]

Land use change

Around 6,000 km² of mangrove was deforested between 1996 and 2016, usually redeveloped for fish and shrimp aquaculture, rice cultivation, palm oil plantations,^[15] and sometimes urbanization.^[39] Diversity of mangrove crabs does not seem to be negatively affected in abandoned aquaculture plots, though logging has significant negative effects on mangrove crab diversity.^[40]

See also

• Fiddler crab
• Sesarmid crabs
• Grapsidae
• Mangrove ecoregions

References