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Many Indo-Pacific mangrove macroinvertebrates are herbivorous and heavily dependent on leaf litter. As a consequence, fallen leaves become a limiting factor and competition occurs among conspecifics and heterospecifics. Neosarmatium meinerti and Cardisoma carnifex are two of the most common herbivorous crabs of the landward mangrove belt in East Africa, often sharing an area and time of activity. This study used a series of field experiments to investigate their feeding habits when co-existing. The high density reached by both species led to overlapping of the individual feeding ranges: during the feeding excursions each crab inevitably encountered, and actively interacted with, other conspecifics and heterospecifics. Competition for food was high: N. meinerti lost approximately 50% of its leaves to theft by C. carnifex. Thus, approximately half of the leaves obtained by C. carnifex were stolen from a foraging N. meinerti. Considering the frequency of such thefts, C. carnifex may be regarded as a facultative kleptoparasitic species. This is the first time that a such strategy has been recorded for a crab species and for a vegetable resource. [ABSTRACT FROM AUTHOR]

The ecology and taxonomy of an interesting species of tree-living freshwater crab from the East Usambara mountains, Tanzania, and from the Shimba Hills, Kenya, East Africa is described. This phytotelmic decapod crustacean belongs to a new species of potamonautid freshwater crab in the genus Potamonautes MacLeay, 1838, which is described. This is one of only a few reports of the phenomenon of the use of water-filled tree holes by any species of true freshwater crab. [ABSTRACT FROM AUTHOR]

The article offers information about the first record of the land crab, Discoplax rotunda, from East Africa. It tries to inquire the geographical distribution of this specie. According to authors, Discoplax rotunda is a land crab inhabiting islands in the Indo-West Pacific oceans, from Aldabra and Mauritius to the Ryukyu Islands, Hawaii, and French Polynesia. The specie commonly lives in the supralittoral or in inland habitats.

This field study investigated the spatial strategies and homing ability of two East African fiddler crabs, Uca lactea annulipes and Uca vocans hesperiae, using various experimental procedures. A clear-cut spatial segregation between the two species was observed, with U. l. annulipes occupying areas even a few centimetres above U. v. hesperiae. Females of both species were extremely faithful to their holes while the males exhibited behavioural differences. U. l. annulipes males were quite faithful to their holes; in contrast, U. v. hesperiae males, during a single low tide, visited several holes which they did not defend. Two displacement experiments were conducted in order to identify the stimuli that fiddler crabs use in their homing. In the ‘dislocation experiment’, the crabs were moved (by hand) 1 or 2 m away from their refuge and released. None of these crabs returned to its burrow and, moreover, the initial directions they followed were not homeward orientated. In the ‘translation experiment’, the crabs were passively translated while actively feeding. When the crabs attempted to go ‘home’ after the translation, they darted along a straight path that led them to points that would have corresponded to their homes if the translation had not taken place. After this first response crabs then commenced searching strategies that led half of them home. Short-range homing seems to depend strongly on information actively gathered during the outward journey, other than local visual landmarks. [ABSTRACT FROM AUTHOR]