Aratus pisonii, commonly known as the Mangrove Tree Crab, is a member of the Grapsidae family (monotypic genus) and is found in the edges of mangrove forests from eastern Florida to northern Brazil on the Atlantic coast and from Nicaragua to Perú on the Pacific coast (Rathbun 1918, Chace and Hobbs 1969 [as cited in Díaz and Conde 1989]). The adults are arboreal and live in the supralittoral zone of the roots, branches, and canopy of mangroves, primarily Rhizophora mangle and Avicennia germinans (Díaz and Conde 1989, Simberloff 1983). They return to the water to drink, to breed, and as a potential escape from predators (Díaz and Conde 1989). The males of this species have a larger carapace width than the females, possibly due to a larger allocation of energy going towards reproduction in the females. Females also tend to have a longer time between molts, a trend that is especially notable in ovigerous females (Díaz and Conde 1989). Multiple studies have found a higher abundance of females compared to males (Díaz and Conde 1989, Conde et. al. 2000). Their diet is primarily composed of mangrove leaves although they have been known to eat filamentous algae, large insects and fish as well (Simberloff 1983, Díaz and Conde 1989). Predation by birds and other crabs such as Goniopsis cruentata have been documented but are not considered to have a large effect on A. pisonii mortality. Occasionally, the crabs will jump into the water in order to escape a predator, often leading to predation by fish (Díaz and Conde 1989). Females lay eggs throughout the year with the majority of females in their last trimester occurring in the rainy season. There is a positive correlation between female carapace width and number of eggs produced with the mean number of eggs per female equaling 11,577 (Díaz and Conde 1989). In Jamaica, the breeding patterns seem to be correlated with lunar cycles. This is thought to be because a high tide will prevent larval stranding (Warner 1967 as cited in Díaz and Conde 1989). In the edges of mangrove forests, larval stranding is not an issue due to the consistently high water level. For this reason, lunar cycles do not seem to have an effect on breeding patterns in these habitats. For individuals of A. pisonii that inhabit the interior of mangrove forests, there is a possible migration to the forest edge for the purpose of breeding, although this has not been verified. Overall, A. pisonii is a sedentary species and has not been shown to migrate (Díaz and Conde 1989). The larva of A. pisonii undergoes 5 aquatic stages: 4 zoeal stages and one megalopal stage, although one study found cases where one or even two of the zoael stages were suppressed (Cuesta et al. 2006, Díaz and Bevilacqua 1987). Each zoeal stage lasts between 4-6 days and the megalopal stage duration has not been determined (Cuesta et. al. 2006).
occurs (regularly, as a native taxon) in multiple nations
Regularity: Regularly occurring
Type of Residency: Year-round
Global Range: (20,000-2,500,000 square km (about 8000-1,000,000 square miles)) Occurs from south Florida, USA, south through the Caribbean (principally the Antilles) to Brazil on the Atlantic coast, and from Nicaragua to Peru on the eastern Pacific coast.
Comments: Roots and branches of mangrove trees (esp. RHIZOPHORA MANGLE) along estuarine to nearly freshwater shorelines.
Water temperature and chemistry ranges based on 2 samples.
Depth range (m): -4 - 1
Temperature range (°C): 27.858 - 27.858
Nitrate (umol/L): 0.255 - 0.255
Salinity (PPS): 33.450 - 33.450
Oxygen (ml/l): 4.615 - 4.615
Phosphate (umol/l): 0.162 - 0.162
Silicate (umol/l): 2.664 - 2.664
Depth range (m): -4 - 1
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.
Non-Migrant: No. All populations of this species make significant seasonal migrations.
Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).
Locally Migrant: No. No populations of this species make annual migrations of over 200 km.
Number of Occurrences
Note: For many non-migratory species, occurrences are roughly equivalent to populations.
Estimated Number of Occurrences: 81 to >300
Life History and Behavior
Molecular Biology and Genetics
Statistics of barcoding coverage: Aratus pisonii
Public Records: 0
Specimens with Barcodes: 1
Species With Barcodes: 1
National NatureServe Conservation Status
Rounded National Status Rank: NNR - Unranked
NatureServe Conservation Status
Rounded Global Status Rank: G5 - Secure
Reasons: Species is fairly widespread. However, habitat is threatened by development, especially in Florida.
Other Considerations: Species is of conservation concern in Florida.
Degree of Threat: B : Moderately threatened throughout its range, communities provide natural resources that when exploited alter the composition and structure of the community over the long-term, but are apparently recoverable
Comments: Shoreline habitat has been and continues to be destroyed or degraded for housing and development, particularly in south Florida.
Global Protection: Unknown whether any occurrences are appropriately protected and managed
Comments: There is some protection for mangroves in Florida, but no direct protection for this species.
Needs: Increased protection/preservation of mangroves; acquisition of some EOs.
Relevance to Humans and Ecosystems
Aratus pisonii, commonly known as the mangrove tree crab, is a species of crab which lives in mangrove trees in tropical and subtropical parts of the Americas, from Florida to Brazil on the Atlantic coast, and from Nicaragua to Peru on the Pacific coast. It feeds mostly on the leaves of the mangroves, but is an omnivore, and prefers animal matter when possible. A. pisonii is the only species in the monotypic genus Aratus. The specific epithet pisonii commemorates the Dutch naturalist Willem Piso who travelled in Brazil in 1638 with Georg Marggraf.
The mangrove tree crab is a small species with males averaging about 2 centimetres (0.79 in) long and females slightly less. The large eyes are set far apart and the carapace is wider at the front than at the back. It is a mottled brown and olive colour which helps the crab to blend in with its surroundings. The legs are either brown or mottled and there are tufts of black hairs near their tips. These are pointed which aids the crab when climbing among the mangrove foliage. 
Distribution and habitat
The mangrove tree crab is found in tropical and semitropical regions along the coasts of North, Central and South America. On the Atlantic side its range extends from Florida to northern Brazil, including the whole Caribbean region. On the Pacific side, it occurs from Nicaragua to Peru. It lives primarily on the red mangrove Rhizophora mangle but is also commonly seen on the white mangrove Laguncularia racemosa and the black mangrove Avicennia germinans, ascending the trees when the tide rises and descending to the exposed mud when the tide goes down.
The mangrove tree crab is an omnivore though the greatest part of its diet is the leaves of the mangrove trees on which it lives. It consumes the epidermis of the leaves and characteristic scraping marks show where it has fed. Even where this crab is uncommon, its consumption may constitute over 90% of the herbivory of mangrove leaves. It also eats organic debris and opportunistically feeds on carrion and small invertebrates including polychaete worms, nematodes and foraminiferans. In feeding trials it was found that this crab prefers animal food over plant food. This is unsurprising considering that mangrove leaves are of poor nutritional value, but what is surprising is the high proportion of leaf matter in the crab's diet. It is possible that this is a response to the greater risk of predation in the water than in the canopy.
The mangrove tree crab is preyed on by birds, terrestrial mammals and larger crabs. It is efficient at evading potential predators as it can scuttle along branches at the rate of one metre (yard) per second and can leap to safety in the water below. Here it may become the victim of a predatory fish.
In northern Brazil, breeding takes place over an extended period but peaks in the rainy season. The female mangrove tree crab carries the fertilised eggs under her abdomen until they are ready to hatch. While they are there she moves to the fringes of the mangrove area where conditions are better for the developing embryos and the release of the newly hatched larvae into the sea. The larvae pass through four zoeal stages and one megalopa stage as part of the plankton over the course of a month.
- "Aratus pisonii". Integrated Taxonomic Information System.
- Peter K. L. Ng, Danièle Guinot & Peter J. F. Davie (2008). "Systema Brachyurorum: Part I. An annotated checklist of extant Brachyuran crabs of the world" (PDF). Raffles Bulletin of Zoology 17: 1–286.
- Amy A. Erickson, Ilka C. Feller, Valerie J. Paul, Lisa M. Kwiatkowski & Woody Lee (2008). "Selection of an omnivorous diet by the mangrove tree crab Aratus pisonii in laboratory experiments". Journal of Sea Research 59 (1–2): 59–69. doi:10.1016/j.seares.2007.06.007.
- Henri Milne-Edwards (1837). Histoire naturelle des crustacés: comprenant l'anatomie, la physiologie et la classification de ces animaux 2. Paris: Librairie encyclopédique de Roret. p. 76.
- Sweat, L. H. (2009-06-08). "Aratus pisonii". Smithsonian Marine Station at Fort Pierce. Retrieved 2012-10-25.
- Erickson, Amy A.; Feller, Ilka C.; Paul, Valerie J.; Kwiatkowski, Lisa M.; Lee, Woody (2008). "Selection of an omnivorous diet by the mangrove tree crab Aratus pisonii in laboratory experiments". Journal of Sea Research 59: 59–69. doi:10.1016/j.seares.2007.06.007.
- de Arruda Leme, Maria Helena; Negreiros-Fransozo, Maria Luciao (1998). "Reproductive patterns of Aratus pisonii (Decapoda: Grapsidae) from an estuarine area of São Paulo Northern Coast, Brazil". Revista de Biología Tropical 46 (3): 673–678.
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