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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).

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