Cladoceran assemblages, seasonal succession and the importance of a hypolimnetic refuge

Abstract

I. We investigate the importance of a refuge from fish predation to the abundance, species composition and seasonal succession of zooplankton. Thirty lakes representing a range of depths were sampled twice in summer for physical/chemical parameters and zooplankton community structure.2. We deHne the refuge from centrarchid predators to be that space between the thentKKline and the zone of anoxia. As lakes vary in rate of oxygen depletion from the hypt»limnion. the refuge size and lake depth are independent: refuge size decreases during the summer period.3. Lake depth and refuge size independently explain variation among lakes in zooplankton species composition, but seasonal community change within lakes is best predicted by loss of refuge size.4. Refuge size also explains the substantial variation in the relative dominance of the two major daphnid species. Lakes possessing a large refuge are dominated by D. ptUicaria: those with a small refuge are dominated by the smaller. D. lialeata mcndotac. We suggest that lakes of intermediate refuge size, which arc characterized by high species diversity, represent a more equitable balance of predation and competition.

Toward a more comprehensive theory of zooplankton diel vertical migration: Integrating ultraviolet radiation and water transparency into the biotic paradigm

“…In these lakes, warm-water fish species dominate and are constrained to feeding in the surface waters. The hypoxic deeper waters may actually act as an important refuge for zooplankton from fish predation (Hanazato et al 1989;Wright and Shapiro 1990;Tessier and Welser 1991) as well as visually feeding invertebrate predators, such as Bythotrephes (Manca et al 2007;Manca and DeMott 2009). In oceans, the more transparent systems are generally associated with warmer, open-ocean, low-latitude habitats, such as subtropical gyres, and therefore, in contrast to freshwater systems, are usually populated by warm-water fish species.…”

“…Evidence for the importance of visual predation in driving DVM also comes from the fact that visual predators are size selective and that smaller, less conspicuous zooplankton often migrate less than large zooplankton (Bollens and Frost 1991b;Gonzalez and Tessier 1997;Thys and Hoffmann 2005). Similarly, there is no question about the effectiveness of DVM in reducing predation risk in more productive, less transparent lakes where fish are abundant and a refuge from visual predators exists between an upper (shallow depth) boundary of low temperature or moderate hypoxia (3 mg L 21 ) that excludes or at least minimizes the abundance of visual predators and a deep boundary of low oxygen (1 mg L 21 ) that constrains zooplankton (Wright and Shapiro 1990;Tessier and Welser 1991;Klumb et al 2004). Seasonally, as this refuge disappears, Daphnia populations decline even though food resources and reproductive rates are sustained.…”

Vertical distribution of pelagial zooplankton in a middle-sized dimictic valley reservoir

“…The hypolimnic refuge of cladocerans against fish is very important for their abundance, species composition and seasonal succession (Tessier & Welser, 1991). In Dubník II, as a consequence of unsuitable conditions in the hypolimnion, daytime refuge for cladocerans is during summer stagnation restricted only to thermocline depth or a layer closely beneath it, as observed in other reservoirs (Lampert, 1989;Jiliberto & Zuniga, 2001;Rautio et al, 2003;Boeing et al, 2004).…”

“…larvae (Horpila et al, 2000). As cladocerans refuge size determines the ratio of large and small cladocerans (Tessier & Welser, 1991), we suggest that the high zooplanktivorous fish stock in Dubník II supports small species of cladocerans not only directly by predation (Hudcovicová & Vranovský, 2000) but also indirectly by a reduction in cladocerans refuges, as unsuitable fish stock contributes to low oxygen content and to the presence of Chaoborus larvae near the bottom. Improvements, also relating to water quality, could be carried out by enhancement of pike-perch Sander lucioperca (L., 1758) and pike Esox lucius (L., 1758) stocks, as recommended in our previous study (Hudcovicová & Vranovský, 2000).…”

Testing zooplankton food limitation across gradients of depth and productivity in small stratified lakes

“…In such systems, Daphnia avoid fish predation by living in the deep-water refuge, or by migrating between surface waters and the deep refuge under cover of darkness. The strong grazing exerted by large-bodied Daphnia is well documented (Carpenter and Kitchell 1993;Tessier et al 2001). However, we have little understanding of how food conditions for grazers vary with depth or trophic state in stratified lakes inhabited by large-bodied Daphnia.…”