Zooplankton eat what they need: copepod selective feeding and potential consequences for marine systems

Abstract

Herbivores are generally faced with a plethora of resources which differ in quality. Therefore, they should be able to select foods which most closely match their metabolic needs. Here, we tested the hypothesis that copepods of the species Acartia tonsa select prey cells based on quality differences within prey species. We assessed age‐specific variation in feeding behaviour and evaluated the potential consequences of such variation for nutrient cycles. Nauplii (young) stages characterized by a low nitrogen to phosphorus (N:P) ratio in their body tissue selected for phosphorus‐rich food, while older copepodite stages with higher body N:P selected for nitrogen‐rich food. Further, the analysis of a 35‐year data set in the southern North Sea revealed a positive correlation between the abundance of nauplii and the ratio of dissolved inorganic N:P, thus suggesting that P‐availability for primary producers declines with the population densities of nauplii. Our findings demonstrate that a combination of stage‐specific selective feeding and body stoichiometry has the potential to affect cycling of limiting nutrients when consumer populations change in composition.

From Elements to Function: Toward Unifying Ecological Stoichiometry and Trait-Based Ecology

“…For instance, experiments in lakes provided evidence that the replacement of the high body N:P copepods with low N:P Daphnia caused a transition from N to P limitation for primary producers (Sterner, 1990;Elser et al, 1996), likely driven by the higher N:P ratio of recycled material (Elser et al, 1988). In addition, intraspecific variation in nutrient recycling traits during copepod ontogeny has been suggested to influence biogeochemical cycling within marine systems (Meunier et al, 2016a). Like zooplankton, aquatic vertebrates such as fish and amphibians can also have important stoichiometric impacts on nutrient cycling and trophic dynamics .…”

“…This has been confirmed in experiments showing that consumers release P at a substantial rate, even when fed high C:P food (Demott et al, 1998;Shimizu and Urabe, 2008). Despite these limitations associated with P losses, e.g., through molting (Shimizu and Urabe, 2008), a large body of literature points toward a negative relationship between Body size Higher mass-specific nutrient recycling by organisms of smaller body size Allgeier et al, 2015;Vanni and McIntyre, 2016 Phylogeny Taxonomic identity affects size scaling and rates of N and P excretion Allgeier et al, 2015 growth rate and body C:P or N:P (e.g., Carrillo et al, 2001;Meunier et al, 2016a). Interestingly, organisms' size and growth rate are usually negatively correlated (Table 1), which implies that, based on the growth rate hypothesis, smaller heterotrophic organisms might generally have lower N:P ratios (Figure 2).…”

“…Grazers however possess a large range of adaptations that allow them to minimize the consequences of these nutrient imbalances. Besides selective feeding (e.g., Kagata and Ohgushi, 2011;Meunier et al, 2012Meunier et al, , 2016a and habitat choice (Winder et al, 2004;Reichwaldt, 2008), consumers may handle poor food quality by selectively retaining and excreting nutrients (Elser and Urabe, 1999;Knoll et al, 2009). These physiological adjustments are tightly linked with the stoichiometry of traits such as elemental ratios of recycled materials and body stoichiometric homeostasis.…”

“…The recognition of the importance of stoichiometric constraints between consumer needs and prey nutrient content has substantially increased our understanding of trophic interactions. For example, high C:P food is often of low-quality for a variety of organisms including molluscs (Stelzer and Lamberti, 2002;Fink and Elert, 2006), crustaceans (Boersma and Kreutzer, 2002;Meunier et al, 2012Meunier et al, , 2016a, insects (Perkins et al, 2004), fish (Borlongan and Satoh, 2001;Vrede et al, 2011), and birds (Grone et al, 1995). ES has therefore proven to be a highly suitable framework in community ecology, explaining consumer responses to prey food quality (food intake, growth, as well as competition between consumer species, and consumer effects on prey nutrient composition (Sterner, 1990;Sterner et al, 1992;Sterner and Hessen, 1994).…”

An Operational Framework for the Advancement of a Molecule-to-Biosphere Stoichiometry Theory

“…There are different ways to measure variability within a population: according to ontogenetic stages (Main et al, 1997;Meunier et al, 2016), driven by a master trait such as body size or reproductive status (Mendez and Karlsson, 2005), controlled by genotypes, environmentally driven (DeMott et al, 2004), or as stochastic inter-individual variability. Teasing apart all these sources of variation is anything but straightforward and only a few attempts have been made so far, revealing a surprisingly large effect of abiotic conditions on supposedly homeostatic organisms (e.g., El-Sabaawi et al, 2012).…”