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

Abstract

We examined the significance of vertical structure in lake plankton to grazer-resource coupling by quantifying how the intensity and mechanism of grazer food limitation varies with depth. We used Daphnia growth assays and also sampled resources (chlorophyll, particulate carbon, and phosphorus) and the day/night depth distributions of Daphnia spp. during summer in four depth strata of lakes that differ in trophic state. The growth assays included treatments with natural seston and seston supplemented with phosphate or Synechococcus, an energy-and P-rich cyanobacterium highly deficient in essential fatty acids and sterols. Results from growth assays and measurements of Daphnia P balance indicate strong energy limitation and weak and sporadic P limitation, despite seston C : P ratios in the upper depth strata above the predicted threshold for Daphnia P limitation. Growth improved with depth and was very high with resources collected from a deep layer of sulfur bacteria that was partially protected from grazing by low dissolved oxygen. Strong positive responses to Synechococcus supplements and high growth with resources from the sulfur bacteria layer are both contrary to limitation by essential lipids. The intensity of food limitation was independent of lake trophic state but was influenced by the quality of the deep-water refuge. Across depths and lakes, food limitation was dependent on Daphnia density; strong food limitation was associated with high Daphnia biomass (Ͼ100 g L Ϫ1) and Daphnia grazing Ͼ20% per day.The coexistence of planktivorous fish and large-bodied Daphnia during summer is dependent on the presence of a deep-water refuge (Wright and Shapiro 1990; Tessier and Welser 1991). 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.Zooplankton migration into surface waters has usually been thought to reflect a trade-off between improved food conditions and increased risk of fish predation (Gliwicz and Pijanowska 1988). However, Williamson et al. (1996) showed that resources from a metalimnetic peak in chlorophyll supported better zooplankton reproduction than resources from surface waters. They also pointed out that subsurface maxima in algal abundance are common, especially in less productive waters. In contrast, Cole et al. (2002) found that resources from surface waters supported better Daphnia growth than resources from the metalimnetic chlorophyll maxima of two oligotrophic lakes. Accumulating evidence shows that food quality is often more important than 1 Corresponding author (demott@ipfw.edu). AcknowledgmentsWe thank Pam Woodruff for technical support and the Albert, Burdick, and Champion families for ac...

Recent blooms of the dinoflagellate <i>Ceratium</i> in Albert Falls Dam (KZN): History, causes, spatial features and impacts on a reservoir ecosystem and its zooplankton

“…Food resources are well known to exert profound effects on zooplankton abundance and composition through one or more major avenues of influence (e.g. Sterner and Schulz, 1998;DeMott et al, 2004;Becker, 2004):…”

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

“…Two important consequences of this are that more transparent lakes have lower food quality (higher carbon : phosphorus [C : P]) in the surface waters (Sterner et al 1997) and that the food in the DCM is likely to be of higher nutritional quality than that in the surface waters (Rothhaupt 1991). A comparison of food quality across lakes of differing transparency showed that both oligotrophic and eutrophic lakes have lower seston C : P ratios (higher food quality) in deeper waters, and that the pattern is stronger in more oligotrophic lakes (DeMott et al 2004). This same study also showed higher particulate carbon concentrations in the deeper waters of both types of lakes, higher edible chlorophyll in the deeper waters of the eutrophic lake, and similar edible chlorophyll across all depths in the oligotrophic lake.…”

“…Studies that have fed zooplankton with seston collected from epilimnetic and deeper waters in controlled experiments frequently reveal equal or higher growth and reproductive rates on the food from deeper waters (Williamson et al 1996a;Winder et al 2003a;DeMott et al 2004). In some cases, the depth of optimal food quality may vary seasonally (Hoenicke and Goldman 1987), and in others, food quality may actually be better in the surface waters (Cole et al 2002).…”

“…The demographic advantage for zooplankton that spend more time in the warmer surface waters of stratified systems has long been recognized: warmer temperatures in the surface waters induce higher growth and reproduction (Orcutt and Porter 1983;Stich and Lampert 1984;Leibold 1989). A combination of this demographic advantage and the fact that food quality is often suboptimal in the surface waters in fact makes temperature likely to be more important than food in creating a vertical habitat structure that leads zooplankton to migrate into the surface waters at night in some systems (Williamson et al 1996a;Winder et al 2003a;DeMott et al 2004). The importance of temperature is apparent from experiments with experimental in situ columns incubated at three depths in a transparent lake.…”

Contrasting patterns of cadmium bioaccumulation in freshwater cladocerans

“…The S f values in the three cladoceran species were estimated for two food concentrations (i.e., 10 4 and 5 3 10 4 cell mL 21 ), both of which are environmentally realistic (DeMott et al 2004). The AE values at the 5 3 10 4 cells mL 21 food level (24.5%, 32.0%, and 57.4% in C. dubia, D. galeata, and M. macrocopa, respectively) were estimated by fitting an exponential decay model with food concentration to the quantified Cd AE (Tan and Wang 2009).…”