Factors Regulating Zooplankton Biomass, Abundance, and Community Structure in a Southcentral Texas Reservoir
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This study focused on zooplankton dynamics in a shallow hard water reservoir during summer months and the influence of reservoir water residence time and off-channel areas on zooplankton dynamics. Thirteen crustacean and eight rotifer taxa were observed. Net zooplankton abundance and biomass, cladoceran abundance and biomass, copepod abundance and biomass, and rotifer abundance and biomass were all significantly related to water residence time and sampling station location (off-channel versus pelagic). I hypothesized that net zooplankton biomass and abundance would be greater in slower flow velocity off-channel areas compared to upstream pelagic sites and that rotifer biomass and abundance would dominate that of crustaceous zooplankton in upstream lotic-like areas. My results showed that net zooplankton abundance and biomass were greater in the off-channel areas and that rotifer abundance was much greater than copepod and cladoceran abundance at the upstream sites. However, rotifer biomass was much lower than that of cladocerans and copepods at these same lotic-like areas. Most of the crustacean zooplankton observed at these upstream areas were large copepods. I suggest that zooplankton abundance and biomass were directly related to water residence time, but that rotifer biomass was also influenced by competition for food with much larger crustaceans. I also suggest that the off-channel areas were used as refuge areas especially when water residence time was below 1 day. During the summer of 2004, Lake Dunlap was highly influenced by heavy rains and high releases from the upstream Canyon Reservoir.