Littoral substrates and nest properties of Coptodon rendalli vary with distance from the shoreline in a tropical impoundment, southeast Zimbabwe

Abstract

The change in littoral substrates and Coptodon rendalli nest properties along the inshore–offshore gradient of Mushandike Dam in southeast Zimbabwe, impacted by long-term water-level fluctuations, were studied in March 2016. Substrate and nest properties were measured in four contiguous 25 m² plots along the inshore–offshore gradient at five sampling stations. We used one-way ANOVA to test for differences between treatments, and multiple linear regression to determine the substrate variables significantly influencing nest characteristics. Percentage sand, pebble/gravel/boulder, coarse organic matter and vegetation significantly declined but clay/silt increased with increasing shoreline displacement. Nest density and diameter significantly decreased with increasing distance from the shore. While vegetation had a positive relationship with nest density and diameter, clay/silt negatively influenced nest diameter indicating that vegetation and substrate properties play an important role in nest establishment by C. rendalli. In conclusion, water-level fluctuations causing large-scale shoreline displacement through changes in littoral substrate properties can, potentially, significantly impact the reproduction of C. rendalli and other such littoral biota, impairing the structure, productivity and composition of littoral communities. Further, these assessment methods are transferrable, efficient and cost effective, enabling the assessment of potential impacts of changing water levels on littoral biota to better inform water management decisions.