Zooplankton-mediated nutrient limitation patterns in marine phytoplankton: an experimental approach with natural communities

Abstract

Zooplankton nutrient recycling has been shown to substantially affect nutrient availability for phytoplankton . However, investigations are required to determine whether zooplankton also influence nutrient limitation in marine phytoplankton communities, and whether grazing by different zooplankton groups results in different patterns of phytoplankton nutrient limitation. We performed laboratory experiments under different nutrient supply conditions on a variety of phytoplankton communities with natural densities of copepods and rotifers, and tested phytoplankton nutrient limitation in bioassays for nitrogen, phosphorus, and the combination of the two. After 5 d incubation with zooplankton, we observed a significant increase in phytoplankton biomass in the zooplankton treatments. We relate this largely to nutrient recycling effects, which are amplified through possible trophic cascade effects. In copepod treatments, the highest phytoplankton biomass was reached under Redfield and nitrogen excess nutrient supply conditions, while the highest biomass in rotifer treatments was registered under phosphorus excess conditions. In most cases, nutrient limitation assays revealed a co-limitation of phytoplankton by nitrogen and phosphorus. With increasing nitrogen supply, we observed an increase in phosphorus limitation in the copepod treatments and a decrease in nitrogen limitation in the rotifer treatments. The phytoplankton community was driven into phosphorus limitation under nitrogen excess conditions in copepod treatments. Our results indicate that natural densities of zooplankton are able to promote nitrogen and phosphorus co-limitation in phytoplankton communities. KEY WORDS: Nutrient limitation · Marine plankton · Zooplankton-driven nutrient recycling · StoichiometryResale or republication not permitted without written consent of the publisher OPEN PEN ACCESS CCESS

Grazers and Phytoplankton Growth in the Oceans: an Experimental and Evolutionary Perspective

“…Our results in experiments involving eukaryotic phytoplankton and copepod grazers are consistent with the report of Trommer et al [24]. We find that protistan grazers also result in increased growth rates for eukaryotic phytoplankton, with the effect of ciliate grazing on our diatom population being significantly stronger than that of copepods.…”

“…In previous research, Trommer et al [24] grew a mixed assemblage of phytoplankton (dominated by diatoms and dinoflagellates) in the absence of grazers and in the presence of either A. tonsa or the rotifer Brachionus plicatilis , finding that phytoplankton biomass increased in the presence of micrometazoan grazers, (although results varied as a function of nutrient availability). Our results in experiments involving eukaryotic phytoplankton and copepod grazers are consistent with the report of Trommer et al [24].…”

Paleobiological Perspectives on Early Eukaryotic Evolution

“…Indeed, Stanley's (1973) early formulation of the predation hypothesis can be applied at least as well to eukaryophagy in protists as it has been to carnivory in animals. Experiments indicate that protistan and micrometazoan grazers both result in increased growth rates and biomass for eukaryotic phytoplankton, but not cyanobacteria (Trommer et al 2012;Ratti et al 2013); thus, eukaryophagy could, in principle, have facilitated the rise of eukaryotic phytoplankton to ecological prominence. Porter (2011) was the first to propose that protistan predation might have driven the observed Neoproterozoic expansion of eukaryotic fossils.…”

Biotic regulation of non-limiting nutrient pools and coupling of biogeochemical cycles

“…For example, zooplankton can affect the availability of nutrients in surface and deep waters through vertical migrations and excretion of part of the nutrients ingested (Elser and Urabe, 1999;Palmer and Totterdell, 2001;Thingstad et al, 2005). This can result in a shift from P or N limitation of autotroph growth to colimitation by the two nutrients simultaneously in freshwater and marine ecosystems (Moegenburg and Vanni, 1991;Trommer et al, 2012). However, consumer-driven nutrient recycling does not necessarily have a positive effect on the growth of autotrophs (Daufresne and Loreau, 2001), and thus on biotic regulation of biogeochemical cycles.…”