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Summary
Morrumbene is a tropical estuary which opens into Inhambane Bay at 23°S on the coast of Moçambique. It is 193 km2 in area and 20 km long with well-developed mangrove swamps draining into a broad lagoon. Temperature, salinity and substrate conditions are described and it is shown that water temperatures in the upper reaches vary from 18,8°C in winter to 28,2°C in summer. The vegetation is described briefly. The fauna was sampled by dredging, netting and intertidal transects along the estuary. It is very diverse. An annotated list shows the distribution of 404 macroinvertebrates and 114 species of fish. The estuary is not highly productive.
The bulk of the fauna is confined to the lagoon and the mangrove swamps in the upper reaches have a restricted and monotonous fauna. All shores are dominated by crabs. Vertical distribution on the shore is controlled by many factors and the depth of the water-table and shade appear to be more important than tidal level.
The fauna includes 70% tropical species, 13% subtropical endemics and 6% Cape endemics. The estuarine fauna of Morrumbene has only 15% similarity to the fauna of an exposed seashore nearby, but 60% similarity to the fauna of the sheltered seashores of Inhaca Island 400 km to the south. The Morrumbene fauna is much richer in species than all the estuaries in Natal or the southern Cape; it is six times richer than all the estuaries on the cold Atlantic coast. Evidence is presented that at the mouths of Atlantic coast estuaries there is a marked temperature barrier in summer and it is suggested that this may limit the estuarine fauna.
