Search

Grapsoid and ocypodoid crabs receive a lot of attention in the literature due to their predominance and important role as primary and secondary consumers in intertidal as well as supratidal marine habitats. They are especially species-rich in the tropics, where they have been found to repeatedly invade terrestrial and freshwater habitats. However, the systematics of the crabs belonging to these two superfamilies is still not settled, despite recent steps clarifying phylogenetic relationships and introducing new taxa. In this study, a molecular phylogeny of grapsoid crabs primarily based on East African representatives is constructed based on DNA sequences of the mitochondrial small and large ribosomal subunits (12S and 16S rRNA), thus complementing previous molecular taxonomic studies that had been carried out with the American and East Asian fauna. In addition, selected representatives of all ocypodoid families and subfamilies were included. The monophyly of Grapsidae, Ocypodidae ( sensu stuctu), Sesarmidae and Varunidae is well confirmed, if the genera Cyclograpsus, Helice are considered Varunidae and Euchirograpsus a Plagusiidae, as previously suggested. The monophyly of the family Gecarcinidae cannot be supported with our data. The family Plagusiidae in its present composition is polyphyletic. Special attention was given to the large family Sesarmidae, which has many endemic genera in the Indo-West Pacific. According to this study, two of the most speciose genera, Chiromantes and Parasesarma, are not monophyletic and need to be redefined. On the higher taxonomic level, it becomes evident that both superfamilies, Grapsoidea and Ocypodoidea, are not monophyletic in their current composition, as exemplified by a proposed sister group relationship of Varunidae and Macrophthalmidae. These results confirm those from previous molecular studies and we therefore propose to refrain from the traditional use of the Grapsoidea and Ocypodoidea as monophyletic superfamilies and treat the constituent families separately. [ABSTRACT FROM AUTHOR]

Eriphia smithi is a very common East African intertidal xanthoid crab. Its dietary input is based mainly in algal grazing (during the day) and predation (particularly at night). Predation appears quite opportunistic and mostly directed at crustaceans and molluscs, among which bivales largely predominate. Echinoderms are actively avoided and, contrary to common belief, predation on Prosobranchia is only accessory. [ABSTRACT FROM AUTHOR]

The relationships between aggressive behaviour and animal density and between aggressive behaviour and metabolic excretion have been investigated in Carcinus mediterraneus Czerniavsky. Increasing the crab density by increasing the number of crabs or reducing the available area revealed that the aggressive interactions perindividual did not increase. The frequency of interactions reached a maximum in several minutes following the introduction of crabs. Individuals isolated between 6 and 24 h were more aggressive than non-isolated ones. The water in which a group of crabs had been held had an inhibitory effect (not abolished by commercial aquarium filters) on aggressiveness of pairs of crabs grater than plain water or water in which single crabs had been kept. No 'home-group' effect was observed. The effect of 'group' water was enhanced by increasing the concentration of crabs in the duration of confinement, and it is probably due to the accumulation of catabolites in the medium. Crabs kept in groups had a greater excretion than isolated crabs and the nitrogen oupput decreased with an increase in the number of crabs or whith a decrease in the size of the tank (with a constant volume of water and number of crabs). [ABSTRACT FROM AUTHOR]

In decapods, no analysis has ever been conducted or the force exerted by chelae, and the role that strength plays in the establishment of hierarchies. For this purpose, a device was designed to measure the force produced by the major chela in the freshwater crab Potamon fluviatile, where dominance hierarchy and agonistic behavioral patterns have previously been analyzed. Experiments showed that only in the females is strength the main factor influencing the outcome of contests. In males chela size more than chela strength is used to settle conflicts, together with other nonphysiognomic characteristics, molding the aggressive state of one individual, such as its history, including isolation from conspecifics, and possibly hormone concentration and metabolic levels. [ABSTRACT FROM AUTHOR]

The behavior and ecology of two mangrove crabs, Sesarma meinerti De Man, 1887 and Cardisoma carnifex (Herbst, 1794) were investigated at the beginning of the rainy season (October-November 1988) at Mida Creek, Kenya. Both species occupy upper intertidal levels, above mean high-water neap, and completely overlap in their zonation. Each burrow lasts ca. 3 wk, with no significant difference between the species. Both are more active around dusk and dawn and also follow a similar trend in their foraging activity, but differ in that burrowing is mainly diurnal in C. carnifex and nocturnal in S. meinerti. A hierarchy of food preference, established by offering C. carnifex and S. meinerti leaves of five mangrove species, proved similar for both, with Bruguiera gymnorhiza ranking first and Avicennia marina last, but significant only for C. carnifex. A rough estimate of the amount of litter consumed by these two species and of the soil mixed up by their burrowing activity indicates that they play a role of primary importance in the ecology of East African mangroves. [ABSTRACT FROM AUTHOR]