Abstract
ABSTRACTZooplankton communities in riverine systems are typically thought to be driven by abiotic forces. However, recent studies have shown that biological controls are capable of structuring these communities in large rivers and may become more influential as a river system becomes more lentic during low discharge. This study uses a long-term data set to examine several environmental variables as potential drivers of zooplankton community structure in a natural riverine lake. We hypothesized that water residence time would be the most important variable influencing zooplankton community structure. To test this, we used non-metric multidimensional scaling and correlation analysis to examine spatial and temporal patterns in zooplankton community structure. Analysis revealed that water residence time was the single most important environmental variable driving zooplankton abundance and community structure. The relationship between water residence time and taxa groups varied indicating that other taxa specific drivers had some influence on zooplankton community structure as well. Continued insight into the mechanisms driving zooplankton community structure will provide a basis for understanding zooplankton dynamics in large river ecosystems.
Highlights
Zooplankton dynamics in lakes are generally considered to be predictable and driven biologically (Sommer et al 1986), whereas zooplankton dynamics in rivers are largely assumed to be driven by physical processes dictated by hydrological variables (Lair 2006)
Spatial and temporal patterns in the zooplankton community were best explained by water residence time while other environmental variables such as water temperature, chlorophyll a and suspended solids did not help to explain the observed patterns
Copepod abundance correlated well with residence time while cladoceran abundance did not always increase with longer water residence time suggesting that biotic controls such as fish predation or food availability may have at times influenced cladoceran dynamics
Summary
Zooplankton dynamics in lakes are generally considered to be predictable and driven biologically (Sommer et al 1986), whereas zooplankton dynamics in rivers are largely assumed to be driven by physical processes dictated by hydrological variables (Lair 2006). While abiotic factors have historically been considered drivers of lotic zooplankton (Hynes 1970), more recent research in large river systems has shown that biological controls are capable of controlling population growth and structuring crustacean zooplankton communities. These studies demonstrated that both top-down and bottom-up trophic interactions are capable of influencing zooplankton community dynamics in river systems through fish predation (Jack & Thorp 2002; Thorp & Casper 2003) and limited algal food resources (Guelda et al 2005). Baranyi et al (2002) found that as water residence time increased on the Danube River system, biological interactions became more important in structuring the zooplankton community
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