Reduced Light Increases Herbivore Production Due to Stoichiometric Effects of Light/Nutrient Balance

Abstract

Ecological common sense says that decreased solar energy should reduce herbivore production because of reduced energy flow through primary producers. However, a field experiment in a phosphorus-limited lake showed that production of zooplankton herbivores was increased by shading. This paradoxical outcome was caused by a decoupling of producer carbon fixation and nutrient uptake under high light that reduced food quality for herbivores. At low nutrient supplies, shading increased nutrient contents relative to carbon within algal food, outweighing effects of decreased primary production. Thus, light/ nutrient balance affects the degree of mismatch between primary producers and herbivores in nature, which in turn influences mass-transfer efficiencies along food chains. To predict how energy transfer efficiency and biological interactions will respond to perturbations, it is essential to take into account changes in light/nutrient balance and its effects on the stoichiometry of autotroph-herbivore interactions.

Light, nutrients, and food-chain length constrain planktonic energy transfer efficiency across multiple trophic levels

“…Production of each trophic level was measured in units of g of C L Ϫ1 ⅐d Ϫ1 to allow us to calculate FCE. We assessed primary production by using 14 C uptake, zooplankton production by using temporal dynamics in body size and egg production, and fish production by using initial and final biomass (see SI Text for details on sample collection and production methods). FCE was quantified as production of the top trophic level divided by PPr.…”

“…Algal cell carbon/nitrogen (C/N) and carbon/phosphorus (C/P) ratios decrease with increasing nutrients and decreasing light intensity (10,12,13), and the ecological efficiency of aquatic herbivores is often higher under low light and/or high nutrient conditions, when algal C/P is relatively low (14)(15)(16). However, other aspects of algal food quality may also covary with stoichiometry, such as morphological features (e.g., size, shape, presence of gelatinous sheaths) and biochemicals (e.g., essential fatty acid and sterol concentrations) (11,17).…”

Interactions between growth-dependent changes in cell size, nutrient supply and cellular elemental stoichiometry of marine Synechococcus

“…The elemental composition of marine phytoplankton is central to ocean biogeochemistry as it links the global carbon (C) cycle with the cycling of other elements, such as nitrogen (N) and phosphorus (P) (Sterner and Elser, 2002;Galbraith and Martiny, 2015). The ratio of elements within organisms is known to vary with energy and nutrient flow through ecosystems (Sterner et al, 1997;Sterner and Elser, 2002;Urabe et al, 2002) and is linked to growth rates and nutritional status. The elemental stoichiometry of biological organisms propagates through the food web to shape community structure and function and in turn, marine biota provides a flexible interface, linking global biogeochemical cycles together and can thereby have large effects on climate systems (Finkel et al, 2010;Galbraith and Martiny, 2015).…”

Seasonal dynamics and life histories of pelagic cladocerans (Crustacea; Cladocera) in an acid boreal lake

“…Due to the two sizeable incoming rivers, the circulating layer of Lake Gjerstadvann was situated at depths which probably exceeded the trophogenic layer (Fee et al 1996;Urabe et al 2002). The inlets transport large amounts of organic matter (both particulate and dissolved) into the lake, associated with heavy rainfalls.…”