The late summer crustacean zooplankton in western U.S.A reservoirs reflects ecoregion, temperature and latitude

Abstract

Summary We tested whether the crustacean zooplankton species composition and size structure (which are important determinants of energy flow in plankton food webs) during late summer in reservoirs would be related to ecoregional designations, catchment land use, temperature and latitude. We also examined whether the predictions of decreasing cladoceran body size with decreasing latitude (as observed for natural lakes) would be valid for reservoirs. Zooplankton samples were collected in late summer 2010 from 102 western U.S. reservoirs distributed over three major ecoregions from 32.5 to 48.6°N latitude. Large‐bodied cladocerans (Daphnia pulex complex) and cyclopoid copepods (Diacyclops thomasi) were found in deeper, cooler reservoirs with forested catchments (Northwestern Forested Mountains). Small‐bodied cladocerans (Daphnia retrocurva, Diaphanosoma spp. and Chydorus sphaericus) and cyclopoid copepods (Tropocyclops prasinus) were more common in productive reservoirs in catchments influenced by agriculture (Great Plains). Small‐bodied cladocerans (Bosmina longirostris) dominated the otherwise modest crustacean zooplankton in reservoirs located in catchments dominated by evergreen shrub vegetation with limited forestation (Western Xeric). Calanoid copepods also displayed clear distribution by ecoregion. Increasing water temperature and decreasing latitude were associated with smaller mean Daphnia and cladoceran body lengths and lower absolute biomass of daphniids. Daphniids were rare or absent in warm waters (i.e. below 36o N latitude and/or from sites located <500 m altitude). Species composition and mean body size of the cladoceran zooplankton were consistent with the feeding habits of the common planktivorous fish – salmon (Oncorhynchus spp.) and lake trout (Salvelinus spp.) in the Northwestern Forested Mountains, gizzard shad (Dorosoma cepedianum) in the Great Plains and threadfin shad (Dorosoma petenense) in the Western Xeric ecoregion. Our study indicates that the taxonomic composition and size structure of the cladoceran zooplankton in reservoirs are highly connected to ecoregional attributes such as catchment land use, temperature and latitude as has been observed for natural lakes.

The freshwater biome gradient framework: predicting macroscale properties based on latitude, altitude, and precipitation

“…Beaver et al. () also found more small bodied species in warmer waters when they assessed 102 western U.S. reservoirs across three ecoregions.…”

Distribution of six taxa in the family Bosminidae Baird (Crustacea: Branchiopoda: Anomopoda) in the plankton of lakes and reservoirs within the continental United States, including expanded range of the invasive cladoceran Bosmina (Eubosmina) coregoni Baird

“…Gizzard shad (Dorosoma cepedianum), an omnivorous pump filter feeder, are widely distributed throughout lakes of the Temperate Plains and Southern Plains (Fuller & Neilson 2017a) and are known to depress the size of crustacean zooplankton communities through predation impacts (Havens & Beaver 2011;Beaver et al 2014). Similarly, threadfin shad (Dorosoma petenense) has been widely stocked in reservoirs of the Western Xeric ecoregion (Fuller & Neilson 2017b) and are highly effective size-selective predators on large-bodied zooplankton crustaceans (Loomis et al 2011;Beaver et al 2014). Distributions of Bosminidae in lakes of the continental U.S. from this study are consistent with the notion that trophic level interactions can favor these small-bodied taxa in the plankton of eutrophic lakes.…”

Echoes of a flood pulse: short-term effects of record flooding of the Illinois River on floodplain lakes under ecological restoration

“…Due to time constraints related to processing time, six samples were randomly selected from each sampling date from Emiquon Preserve (n = 2 per habitat) for analysis. Samples were analyzed using the Utermohl sedimentation technique with a minimum count of 200 organisms (Lund et al, 1958;Beaver et al, 2014). Counts were conducted at 9100 magnification and densities were estimated as numbers l -1 based on the volumes of water that were sampled.…”