Coupling Fish Community Structure with Instream Flow and Habitat Connectivity between Two Hydrologically Extreme Years

Abstract

AbstractHydrologic variability and instream habitat connectivity play fundamental roles in structuring fish communities in lotic ecosystems. We collected fish assemblage and physical habitat data from 28 central Texas streams during the summers of 2006 (a drought year with minimal summer precipitation and low stream flow) and 2007 (an exceptionally wet year with periodic flooding in spring and sustained high flows throughout summer). We evaluated the correspondence between the magnitude of physical habitat and fish community composition change in stream reaches sampled in these two contrasting years using ordination, successional vector analysis, and indicator species analysis. In 2006, streams characterized by disconnected pools had different fish community structure and habitat characteristics than streams that had habitats connected by flowing water. The amount of interannual change in both fish community structure and habitat characteristics was greatest between streams that had disconnected pools in 2006 and their paired samples in 2007. Indicator species analysis identified species that had affinities to disconnected habitats during 2006, which included opportunistic life history strategists typical of temporary waters (western mosquitofish Gambusia affinis and blackstripe topminnow Fundulus notatus) and equilibrium strategists that rely on stable pool habitats for nesting (longear sunfish Lepomis megalotis and largemouth bass Micropterus salmoides). Conversely, indicator species of connected riffle–pool habitat included fluvial specialists (central stoneroller Campostoma anomalum, spotted bass Micropterus punctulatus, and bullhead minnow Pimephales vigilax). In summer 2007, the numbers of most species of fish declined markedly compared with 2006. Community structure between previously disconnected and connected stream types was also highly variable in 2007. However, strong recruitment of juveniles following spring flooding and sustained high summer flow significantly increased the frequency and abundance of two periodical strategists, channel catfish Ictalurus punctatus and flathead catfish Pylodictus olivaris in both types of streams in 2007. These findings provide important insights into how individual species’ life history strategies influence the response of fish community structure to extreme hydrologic events, which are likely to increase in frequency in many parts of the world due to climate change.