Restoration of the annual flood pulse in Breton Sound, Louisiana, USA: Habitat change and nekton community response

Abstract

Riverine pulse events are hypothesized to benefit estuarine nekton resources by making high-quality habitat available for exploitation; however, few studies focus on the actual nekton use of this ephemerally flooded habitat during the flood pulse event. We evaluated the effects of pulsed freshwater flow on nekton density, biomass, diversity and community assembly through 2 winter/spring (February and March) experimental high-flow riverine discharge events in the upper reaches of the Breton Sound estuary, Louisiana, USA in 2005. Nekton were caught with a 1 m 2 drop sampler at flooded vegetated marsh sites in areas both receiving (inflow) and not receiving (reference) pulsed freshwater flow. Inflow marsh sites had significantly greater water depth and were flooded for over twice as long as reference marshes. Significantly higher nekton density and biomass were found at flooded inflow marsh sites than reference marsh sites. Nekton communities were similar and dominated by estuarine resident species (Palaemonetes paludosus, Heterandria formosa, Gambusia affinis, Lucania parva, Poecilia latipinna, Cyprinodon variegatus). The C-score metric (EcoSim) indicated that while initial colonization (1 to 3 d) of flooded sites was random, species assembly following longer-term flooding (7 to 10 d) suggested non-random colonization (p < 0.0001; EcoSim) and supported the coexistence principle. Despite significant coexistence, subtle differences in community assembly were seen among the resident guild, with evidence of segregation driven by water depth (p = 0.002; canonical correspondence analysis). © Inter-Research 2007.