Rotifer–crustacean interactions in a pseudokarstic lake: influence of hydrology Ulrike Obertegger Æ Andrea Borsato Æ Giovanna Flaim Received: 14 December 2008 / Accepted: 5 August 2009 Ó Springer Science+Business Media B.V. 2009 Abstract Zooplankton abundance was related to hydrological and environmental variables in a hydro- logically dynamic lake fed by a pseudokarstic aquifer. The study period (2002–2006) in Lake Tovel covered different hydrological situations with water residence time (WRT) having the lowest values in 2002 and the highest values in 2003. WRT was negatively corre- lated with silica concentrations and algal biovolume. Furthermore, the biovolume of small algae was highest in spring and summer, while large algae did not show any pattern. In multivariate analysis, high abundance of crustacean species in autumn and winter was positively related to WRT and negatively to algal biovolume, while high abundance of rotifer species in spring and summer was negatively related to WRT and positively to algal biovolume. With the exception of Keratella cochlearis and Gastropus stylifer, rotifers showed a pattern of crustacean avoidance, and three groups were distinguished: (i) Ascomorpha ecaudis and Polyarthra dolichoptera, (ii) Asplanchna prio- donta and Synchaeta spp., and (iii) Filinia terminalis and Keratella quadrata. These groups were associated with different food sources and depths. We suggest that WRT influenced the rotifer–crustacean relation- ship by wash-out effects and competition for food resources. The dynamics of single rotifer species were attributable to specific feeding requirements and adaptations. In summary, WRT determined the plat- form for abiotic and biotic interactions that influenced population dynamics of crustaceans and rotifers. Keywords Water residence time Á Zooplankton Á Algal food Á Competition Á Depth preference Introduction Limnology has moved forward from treating lakes as isolated basins to studying them as complex ecosys- tems influenced by their catchments and surroundings. Exterior factors such as solar irradiance, allochtho- nous nutrient input, water inflow and anthropogenic impacts affect the dynamics of organisms living within an ecosystem (Wetzel 2001). Much is known about the influence of several internal factors such as temperature (Gillooly et al. 2002), oxygen (Mikschi 1989), food availability (Pourriot 1977), predation (Brooks and Dodson 1965) and competition (Declerck et al. 2003) on zooplankton dynamics. In the last decade, however, many studies in reservoirs, ponds and rivers have shown that different aspects of water U. Obertegger (&) Á G. Flaim IASMA Research and Innovation Centre, Fondazione Edmund Mach, Environment and Natural Resources Area, Via E. Mach 2, 38010 San Michele all’Adige, TN, Italy e-mail: ulrike.obertegger@iasma.it A. Borsato Museo Tridentino di Scienze Naturali, Via Calepina 14, 38100 Trento, TN, Italy 123 Aquat Ecol DOI 10.1007/s10452-009-9285-0