Mangrove crabs are crabs that live in and around mangroves. They belong to many different species and families and have been shown to be ecologically significant by burying and consuming leaf litter. [1] [2] [3] [4] Mangrove crabs have a variety of phylogenies because mangrove crab is an umbrella term that encompasses many species of crabs. [5] Two of the most common families are sesarmid and fiddler crabs. [6] They are omnivorous and are predated on by a variety of mammals and fish. [7] [8] They are distributed widely throughout the globe on coasts where mangroves are located. [9] [10] Mangrove crabs have wide variety of ecological and biogeochemical impacts due to the biofilms that live in symbiosis with them as well as their burrowing habits. [11] [12] [13] Like many other crustaceans, they are also a human food source [14] and have been impacted by humans as well as climate change. [15]
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 the Indo-West Pacific region in mudflats along tropical coasts. [10] The largest habitats for mangrove crabs are in Southeast Asia, South America, and Northern Australia. [9] As their name suggests, they are primarily found among mangrove tree forests and form symbiotic 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 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]
When young, mangrove crabs get most of their nutrients from polychaete worms and a multitude of microorganisms found living in the sediments and leaves of their environment. [20] As they grow older mangrove crabs are generally detritivores with their diet consisting of already dead organic material. Mangrove crabs consume a large amount of plant material but are primarily omnivorous. [21] In the mangrove 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 the crab plover among other protected species. [17] To protect themselves the crabs can climb trees. [25] The only other crustaceans that climb trees are hermit 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 low tide, allowing them to maintain more constant and ideal temperatures and oxygen levels. These constants can additionally aid other small benthic fauna, like polychaetes and juvenile crabs. [27] Mangrove crabs may plug their burrows at intervals determined by their circadian 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 decreasing erodibility. [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 both abiotic factors like soil composition, and biotic factors like root depth and tree density. [1]
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 coprophagous food chain which contributes to mangrove secondary production. [34] [35]
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]
Ideal mangrove crab habitats rely heavily on coastal depth and surface temperature. [9] Climate change due to anthropogenic 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 shrinks genetic 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, 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]
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]
A mangrove is a shrub or tree that grows mainly in coastal saline or brackish water. Mangroves grow in an equatorial climate, typically along coastlines and tidal rivers. They have particular adaptations to take in extra oxygen and remove salt, allowing them to tolerate conditions that kill most plants. The term is also used for tropical coastal vegetation consisting of such species. Mangroves are taxonomically diverse due to convergent evolution in several plant families. They occur worldwide in the tropics and subtropics and even some temperate coastal areas, mainly between latitudes 30° N and 30° S, with the greatest mangrove area within 5° of the equator. Mangrove plant families first appeared during the Late Cretaceous to Paleocene epochs and became widely distributed in part due to the movement of tectonic plates. The oldest known fossils of mangrove palm date to 75 million years ago.
An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environments and are an example of an ecotone. Estuaries are subject both to marine influences such as tides, waves, and the influx of saline water, and to fluvial influences such as flows of freshwater and sediment. The mixing of seawater and freshwater provides high levels of nutrients both in the water column and in sediment, making estuaries among the most productive natural habitats in the world.
A salt marsh, saltmarsh or salting, also known as a coastal salt marsh or a tidal marsh, is a coastal ecosystem in the upper coastal intertidal zone between land and open saltwater or brackish water that is regularly flooded by the tides. It is dominated by dense stands of salt-tolerant plants such as herbs, grasses, or low shrubs. These plants are terrestrial in origin and are essential to the stability of the salt marsh in trapping and binding sediments. Salt marshes play a large role in the aquatic food web and the delivery of nutrients to coastal waters. They also support terrestrial animals and provide coastal protection.
The fiddler crab or calling crab can be one of the hundred species of semiterrestrial marine crabs in the family Ocypodidae. These crabs are well known for their extreme sexual dimorphism, where the male crabs have a major claw significantly larger than their minor claw, whilst females claws are both the same size. The name fiddler crab comes from the appearance of their small and large claw together, looking similar to a fiddle.
Detritivores are heterotrophs that obtain nutrients by consuming detritus. There are many kinds of invertebrates, vertebrates, and plants that carry out coprophagy. By doing so, all these detritivores contribute to decomposition and the nutrient cycles. Detritivores should be distinguished from other decomposers, such as many species of bacteria, fungi and protists, which are unable to ingest discrete lumps of matter. Instead, these other decomposers live by absorbing and metabolizing on a molecular scale. The terms detritivore and decomposer are often used interchangeably, but they describe different organisms. Detritivores are usually arthropods and help in the process of remineralization. Detritivores perform the first stage of remineralization, by fragmenting the dead plant matter, allowing decomposers to perform the second stage of remineralization.
Bioturbation is defined as the reworking of soils and sediments by animals or plants. It includes burrowing, ingestion, and defecation of sediment grains. Bioturbating activities have a profound effect on the environment and are thought to be a primary driver of biodiversity. The formal study of bioturbation began in the 1800s by Charles Darwin experimenting in his garden. The disruption of aquatic sediments and terrestrial soils through bioturbating activities provides significant ecosystem services. These include the alteration of nutrients in aquatic sediment and overlying water, shelter to other species in the form of burrows in terrestrial and water ecosystems, and soil production on land.
Mangrove forests, also called mangrove swamps, mangrove thickets or mangals, are productive wetlands that occur in coastal intertidal zones. Mangrove forests grow mainly at tropical and subtropical latitudes because mangrove trees cannot withstand freezing temperatures. There are about 80 different species of mangroves, all of which grow in areas with low-oxygen soil, where slow-moving waters allow fine sediments to accumulate.
Eunicidae is a family of marine polychaetes. The family comprises marine annelids distributed in diverse benthic habitats across Oceania, Europe, South America, North America, Asia and Africa. The Eunicid anatomy typically consists of a pair of appendages near the mouth (mandibles) and complex sets of muscular structures on the head (maxillae) in an eversible pharynx. One of the most conspicuous of the eunicids is the giant, dark-purple, iridescent "Bobbit worm", a bristle worm found at low tide under boulders on southern Australian shores. Its robust, muscular body can be as long as 2 m. Eunicidae jaws are known from as far back as Ordovician sediments. Cultural tradition surrounds Palola worm reproductive cycles in the South Pacific Islands. Eunicidae are economically valuable as bait in both recreational and commercial fishing. Commercial bait-farming of Eunicidae can have adverse ecological impacts. Bait-farming can deplete worm and associated fauna population numbers, damage local intertidal environments and introduce alien species to local aquatic ecosystems.
The tall-stilt mangrove belongs to the Plantae kingdom under the Rhizophoraceae family. R. apiculata is distributed throughout Southeast Asia and the western Pacific islands.
Parasesarma erythrodactyla, also known as the red-handed shore crab, is a burrowing crab inhabiting mangrove forests in Australia and Southeast Asia. It is immediately identifiable by its bright red chelipeds (claws) and green/brown carapace.
Brackish marshes develop from salt marshes where a significant freshwater influx dilutes the seawater to brackish levels of salinity. This commonly happens upstream from salt marshes by estuaries of coastal rivers or near the mouths of coastal rivers with heavy freshwater discharges in the conditions of low tidal ranges.
Low marsh is a tidal marsh zone located below the Mean Highwater Mark (MHM). Based on elevation, frequency of submersion, soil characteristics, vegetation, microbial community, and other metrics, salt marshes can be divided to into three distinct areas: low marsh, middle marsh/high marsh, and the upland zone. Low marsh is characterized as being flooded daily with each high tide, while remaining exposed during low tides.
Mangrove ecosystems represent natural capital capable of producing a wide range of goods and services for coastal environments and communities and society as a whole. Some of these outputs, such as timber, are freely exchanged in formal markets. Value is determined in these markets through exchange and quantified in terms of price. Mangroves are important for aquatic life and home for many species of fish.
The mangroves of the Straits of Malacca are found along the coast of Thailand, Malaysia, Singapore and northern Sumatra. These tropical mangrove forests are highly diverse, and are important wetlands with high conservation values. There are two Ramsar sites along the Strait of Malacca: Pulau Kukup and Tanjung Piai.
Ucides cordatus, the swamp ghost crab, is one of two species of crabs in the genus Ucides. This species of crab is native to many coasts off of the western Atlantic Ocean. It has been found to be native to areas as far as Florida, to as southern as Uruguay. U. cordatus is especially noteworthy in the country in Brazil as it plays important roles in the economy and food resources at Brazil’s Atlantic borders.
The violet vinegar crab is a swimming crab species in the genus Episesarma. Distributed all over marine and brackish waters of Indo-West Pacific regions. It is harvested by many local fishermen for rich proteinaceous food.
Perisesarma guttatum, the red-claw mangrove crab, is a crab species in the genus Parasesarma and the family Sesarmidae. It is distributed in coastal brackish water habitats of the western Indian Ocean.
Leptuca thayeri, known generally as the Atlantic mangrove fiddler crab or mangrove fiddler, is a species of true crab in the family Ocypodidae. It is distributed all across the Western Atlantic.
Anne E. Giblin is a marine biologist who researches the cycling of elements nitrogen, sulfur, iron and phosphorus. She is a Senior Scientist and Acting Director of the Ecosystem Center at the Marine Biological Lab.
A marine coastal ecosystem is a marine ecosystem which occurs where the land meets the ocean. Worldwide there is about 620,000 kilometres (390,000 mi) of coastline. Coastal habitats extend to the margins of the continental shelves, occupying about 7 percent of the ocean surface area. Marine coastal ecosystems include many very different types of marine habitats, each with their own characteristics and species composition. They are characterized by high levels of biodiversity and productivity.
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