Influence of zooplankton stoichiometry on nutrient sedimentation in a lake system

Abstract

We explored rates and stoichiometry (C : N : P ratios) of sinking particles in a temperate reservoir during a 2-yr period. Plankton was sampled weekly, and a sediment trap placed below the metalimnion collected sinking particles. There were no significant relationships between the stoichiometry of entrapped material and seston or zooplankton stoichiometry. However the differences in the entrapped C : P and N : P ratios between consecutive trap samplings were negatively correlated with the time variations of the zooplankton C : P and N : P ratios. Zooplankton C : P and N : P ratios were positively correlated with the percentage of copepod biomass in total zooplankton biomass Ͼ250 m and negatively correlated with the percentage of cladocerans. Zooplankton biomass Ͼ250 m reduced the fraction of N and P primary production lost to sinking (export ratio). The residuals of the N export ratio versus zooplankton biomass relationship were negatively correlated with the zooplankton N : P ratio, whereas there was a positive relationship with the residuals of the P export ratio relationship. These observations support the hypothesis that the regulation of elemental homeostasis in the herbivorous zooplankton consumers occurs at least partly at the assimilation/egestion level. Elements ingested in excess-P for the herbivorous copepods and N for many cladocerans-are concentrated into sinking feces, whereas the deficient elements are captured into biomass.In lakes, the vertical flux of small particulate matter essentially comprises two components: the sinking of ungrazed phytoplankton cells (e.g., Reynolds et al. 1982) and the sinking of the feces or fecal pellets of planktonic primary consumers (Sarnelle 1999). Both types of particles will settle from the upper layer below the thermocline if their sinking rates are higher than their mineralization rates. A simple heuristic model (Elser et al. 1995) explicitly represents the processes involved (Eq.

Ecological stoichiometry of indirect grazer effects on periphyton nutrient content

“…Some elements are supplied at higher relative rates than they are needed, and consumers excrete these excess nutrients or-in the case of excess carbon -increase their respiration (Darchambeau et al 2003;Anderson et al 2005;Frost et al 2005a). Such consumerdriven nutrient cycling is stoichiometrically constrained (Elser and Urabe 1999) and has been shown to aVect available nutrient ratios in terrestrial (Carline et al 2005) and aquatic (Vanni et al 2002;Frost et al 2004;Darchambeau et al 2005) ecosystems. Models have indicated that herbivore-driven nutrient cycling can alter plant nutrient limitation (Daufresne and Loreau 2001) and plant competition (Grover 2002).…”

“…It has played a special role in community ecology in order to explain consumer responses to prey quality (food intake, growth) (Cross et al 2003;Fagan and Denno 2004;DeMott and Pape 2005), competition between consumer species (Hall 2004;Loladze et al 2004) and consumer eVects on prey nutrient composition (Daufresne and Loreau 2001;Hessen et al 2002;Urabe et al 2002). In addition, ES has provided new and comprehensive explanations for wholeecosystem patterns in nutrient Xuxes and food web structure (Elser 2000;Elser et al 2000b;Darchambeau et al 2005).…”

Influence of food web structure on the biochemical composition of seston, zooplankton and recently deposited sediment in experimental freshwater mesocosms

“…Changes in food web structure by fish manipulations might have an important impact on the biochemical composition of the zooplankton compartment. As suggested by the studies of Elser and Foster (1998), Darchambeau et al (2005), and Danger (2007), changes in the quantity and nature of seston and zooplankton might in turn influence the chemical composition of sinking organic matter and deposited organic matter quality.…”

Plant coexistence depends on ecosystem nutrient cycles: Extension of the resource-ratio theory

“…For example, the activity of grazers can cause nutrients to be lost across system boundaries by means of plant-unavailable pathways. Examples include sedimentation of nutrient-rich particles from pelagic ecosystems due to selective assimilation processes (28,29), vertical migration of zooplankton causing spatially decoupled assimilation and excretion of key nutrients (cf. ref.…”