Wetland edges as peak refugia from an introduced piscivore

1. Wetlands in the Lake Victoria basin serve as structural and hypoxic refugia for some native fishes against predation by introduced Nile perch (Lates niloticus); however, little is known about the fine-scale patterns of distribution and abundance of these refuge inhabitants. 2. This study sought to quantify wetland ecological gradients and determine where peaks in native fish abundance and richness (‘peak refugia’) occurred using Lake Nabugabo, Uganda as a model system. 3. Extensive wetland transects were sampled between June and August, 2011 to measure ecological variation over distance from the lake–wetland edge. 4. Wetlands were characterized by strong clines in water temperature, pH, dissolved oxygen (DO), depth and vegetation density, and narrow peak refugia were found precisely at the lake–wetland edge. Community richness and diversity tended to be greater in areas with higher DO and lower temperature, pH, and vegetation density. It is interesting that areas encroached upon by a native emergent macrophyte (hippo grass, Vossia cuspidata) had more extreme physico-chemical conditions and supported fewer native fish species. 5. These results demonstrate the importance of wetland edges in the maintenance of native fish fauna in the Lake Victoria basin, and suggest that the continued expansion of hippo grassmay reduce the accessibility of wetlands as refugia. 6. We recommend that the use of spatially explicit management approaches such as the development of secure buffer zones surrounding wetland edges to protect peak refugia, and the need for hippo grass control to minimize its effects on this important refuge