Feeding of Sesarma meinerti de Man was studied in the laboratory and at the Beachwood Mangrove Reserve. In the field, mangrove leaf litter formed 74,6% of the diet. Crabs showed a preference for leaves in the order: yellow Bruguiera gymnorrhiza (L.) Lam. > yellow Avicennia marina (Forssk.) Vierh. > green B. gymnorrhiza > green A. marina. In the laboratory, a positive correlation was observed between relative consumption and degree of decomposition ..Crabs fed with both tannin and tannin-free leaves showed a preference for the latter. Removal of B. gymnorrhiza leaves by S. meinerti was high throughout the year, whereas dry mass loss attributable to consumption varied according to season. It is suggested that S. meinerti plays an important role in the degradation of mangrove leaf litter.
151Mangroves are highly productive ecosystems and mangrove detritus has been shown to provide the basis for a complex estuarine foodweb (Golley et al. 1962, Odum and Heald 1972, Lugo and Snedaker 1974, Teas 1976. Hence, much research has concentrated on the fate of mangrove leaf litter. In South Africa and elsewhere (Fell et al. 1975, Cundell et al. 1979, Kohlmeyer and Kohlmeyer 1979, Steinke et al. 1990, Singh and Steinke 1992, studies have been conducted on the role of fungi and bacteria on the breakdown of mangrove leaf litter. However, little work has assessed the role of leaf-burying mangrove crabs in leaf-processing in southern Africa, although this has received attention in the east Indo-Pacific regions (Malley 1978, Nakasone and Agena 1984, Leh and Sasekumar 1985, Robertson 1986, Lee 1989.Sesarma meinerti de Man, the red mangrove crab, is the largest and most striking sesarmid crab in southern African mangrove swamps. Although it is said to be common from the Mbashe Estuary to Inhambane (Day 1974), it also occurs commonly in several estuaries south of Transkei (TDS, pers. obs.). These crabs feed on fallen mangrove leaves and other plant material, although they are generally recognized as being omnivorous scavengers (Macnae 1968, Day 1974, Berjak et al. 1977).
STUDY AREAThe main field study was conducted in the Beachwood mangroves at the mouth of the Mgeni River (29°48'S, 31 0 03'E). The mangrove communities of the Beachwood area have been described by Raiman (1986). The main mangrove species are Bruguiera gymnorrhiza (L.) Lam. and Avicennia marina (Forssk.) Vierh., although Rhizophora mucronata Lam. is also present. For most of the fieldwork of this study a stand dominated by B. gymnorrhiza was chosen near the mouth. The stand, which decreases in height from 7 m near the water's edge to 3 m at the landward margin, experiences tidal coverage only at spring tides. Running through the stand is a creek which occurs as a narrow, shallowsided depression, dry except at high tides. Work in a stand of A. marina was restricted to determinations of the density of crab holes in a well-developed stand (9 m) which lines the streambanks and is inundated at most high tides.At St Lucia Estuary (28°22'S, 32°25'E), density of
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