Coral-inhabiting swimming crabs (Crustacea, Decapoda, Portunidae) of the Sudanese Red Sea

Brachyuran crabs show high species richness and constitute one of the most diverse biotic groups in coral reef communities. The present study examines the taxonomy and ecology (occurrence in particular coral habitats) of swimming crabs from the Sanganeb Atoll (Sudan) known for its high diversity of hermatypic corals. During two expeditions in the years 1991 and 1992, eleven species were collected directly from coral colonies or in baited traps in coral habitats: Carupa tenuipes Dana, 1852; Caphyra fulva Stephenson & Campbell, 1960; Portunus aff. iranjae Crosnier, 1962; Gonioinfradens paucidentata (A. Milne-Edwards, 1861); Thalamitoides quadridens A. Milne-Edwards, 1869; Thalamitoides spinigera Nobili, 1905; Thalamita cf. iranica Stephensen, 1945; Thalamita murinae Zarenkov, 1971; Thalamita prymna (Herbst, 1803); Thalamita quadrilobata Miers, 1884; and Thalamita savignyi A. Milne-Edwards, 1861. Thalamita murinae, had been recorded only once before and incompletely described; it is redescribed from the holotype. Together with Thalamita longifrons (A. Milne-Edwards, 1869) from the Pacific, it forms a distinct group of species living in complex coral habitats. This Th. longifrons group is revised; Th. spinimera Stephenson & Rees, 1967 and Th. yoronensis Sakai, 1969 are considered as new junior synonyms of Th. longifrons. The distribution of swimming crabs across the range of sampled habitats showed a characteristic pattern that did not simply reflect the sampling effort. Thalamitoides spinigera, a species endemic to the Red Sea and the Gulf of Aden, clearly preferred dead Stylophora habitats. Several hypotheses explaining preferences of particular species for Stylophora colonies are discussed. Inhabiting various coral habitats (which for many species can be substituted by rock, rubble or mussel clumps) is characteristic for the subfamilies Carupinae and Thalamitinae, whereas Portuninae are found there occasionally only.