Effect of main-stem dams on zooplankton communities of the Missouri River (USA)

Abstract

The persistence of plankton in flowing water presents an enigma, i.e., how can populations be sustained while constantly losing individuals downriver? We examined the distribution and abundance of zooplankton from 146 sites on the Missouri River (USA) and found large shifts in the dominance of major taxa between management zones of this regulated river. Crustacean zooplankton were dominant in the inter-reservoir zone of the river, and their taxonomic composition was similar to regional lakes and reservoirs. The exponential decline of cladocerans and copepods with distance from main-stem dams suggests that conditions within the river are adverse to population growth and that reservoirs are the main source of these crustaceans in the river. Rotifers dominated in the channelized zone of the river. High algal biomass and rapid population growth rates likely allow persistence of rotifers in segments of the river that do not receive direct reservoir inputs. Rotifers were less abundant in the inter-reservoir zone, suggesting that their numbers are limited by internal processes, such as food or predators. Since zooplankton are known to be an important food for larval fishes in rivers, this shift of major taxa in regulated rivers has implications for river food webs.

Phytoplankton abundance and contributions to suspended particulate matter in the Ohio, Upper Mississippi and Missouri Rivers

“…Inferred grazing rates for the three rivers largely reflect the high abundance of rotifers obtained from microzooplankton (20 lm) samples. The prevalence of rotifers and other small-bodied zooplankton in rivers has been attributed to faster growth rates that allow populations to attain higher density during transport along the river course (Lair 2006;Havel et al 2009). Recent work also suggests that rotifers may be less sensitive to detrimental effects associated with turbulence (Sluss et al 2008).…”

“…Sampling methods for benthic (dreissenid mussels) and pelagic (zooplankton) grazers are described in detail elsewhere (Grigorovich et al 2008;Havel et al 2009) and summarized here. Micro-and macro-zooplankton samples were collected by pumping water from three depths at each of three cross-channel locations (as for CHLa, TSS and POC).…”

Seasonal zooplankton dynamics in main channel and backwater habitats of the Upper Mississippi River

“…Although fish diversity has been extensively studied in large river habitats, the ecology of crustacean and rotifer zooplankton in large river ecosystems has received less attention and community information for these taxa in the UMR is lacking. Recent studies in rivers have shown that zooplankton can achieve substantial densities despite the advective forces inherent in rivers (May & Bass, 1998;Reckendorfer et al, 1999;Kim & Joo, 2000;Dettmers et al, 2001;Havel et al, 2009). While large river zooplankton studies have focused primarily on the main channel, only a few more recent studies have simultaneously examined adjacent backwater communities (Wahl et al, 2008;Sampson et al, 2009).…”

Net autotrophy in a fluvial lake: the relative role of phytoplankton and floating-leaved macrophytes

“…The resulting environment is composed of hybrid features, with both lotic and lentic characteristics (Friedl and Wüest 2002). A limited number of studies have analyzed the effect of river damming on zooplankton and algal communities (Blinn et al 1998;Havel et al 2009), and on primary productivity, and carbon, nitrogen and phosphorus budgets (Nowlin et al 2005;Teodoru and Wehrli 2005). Friedl and Wüest (2002) noted that the ecological consequences of constructed reservoirs may become evident and after long periods (many years).…”