Variation in Invertebrate and Fish Communities Across Floodplain Ecotones of the Altamaha and Savannah Rivers

Abstract

In floodplains of large rivers, different ecotones—zones of transition between adjacent ecological systems—develop where the river and uplands interact with the floodplain. Unique communities of invertebrates and fish may develop in each of these ecotones and in the floodplain interior. In our study, we sampled the river-floodplain ecotone, the upland-floodplain ecotone, and the interior of floodplains of the Altamaha and Savannah Rivers, Georgia, USA to assess how water quality, invertebrate community structure, total invertebrate abundance and biomass, and fish abundance and species richness varied across floodplains. In terms of water quality, electrical conductivity was greatest in the river-floodplain ecotone, while pH and temperature did not vary among sites. Nonmetric multidimensional scaling ordination indicated that overall invertebrate community composition across the floodplain was similar, and was dominated by wetland organisms that likely reside permanently on the floodplain. Total abundance and biomass of invertebrates was greater in the river-floodplain ecotone than the upland-floodplain ecotone, with levels in the floodplain interior being intermediary. Fish abundance and species richness was greater in the river-floodplain ecotone than other sites. Managers should consider lateral variation in invertebrate and fish assemblages across floodplains when planning management of river-floodplain ecosystems.