Longitudinal variation in community structure of floodplain fishes along two rivers of the southeastern USA

Abstract

Many studies have examined whether longitudinal variation exists in fish communities within stream channels. Yet despite the acknowledged importance of adjacent floodplain ecosystems, no study has investigated longitudinal variation in fish communities in floodplain wetlands. We conducted a study to determine if distinct fish communities exist between upper and lower river floodplains. We predicted that floodplains in the upper portions of a watershed will be dominated by opportunistic riverine fish. In contrast, floodplains farther downstream in the watershed will primarily consist of obligate floodplain fishes. We sampled fishes at 21 floodplain sites along the lengths of the Oconee–Altamaha and Broad–Savannah river systems of Georgia, USA, during the 2008 and 2009 flood seasons. A modified mark–recapture method was utilized to estimate probabilities of species detection and occupancy. Ordination and analysis of similarity using species site occupancy estimates identified two unique communities related to floodplain position, and indicator species analysis supported our hypothesis of community distinction based on life history traits. Water resource managers should consider how flood pulse character influences fish communities when regulating flow regimes.