Differential effects of nutrient-limited primary production on primary, secondary or tertiary consumers

Abstract

Nutritional imbalances between predator and prey are the rule rather than the exception at the lower end of food webs. We investigated the role of different grazers in the propagation of nutritionally imbalanced primary production by using the same primary producers in a threetrophic-level food chain and a four-trophic-level food chain experimental setup. The three-trophic-level food chain consisted of a classic single-cell primary producer (Rhodomonas salina), a metazoan grazer (the copepod Acartia tonsa) and a top predator (the jellyfish Gonionemus vertens), while we added a protozoan grazer (Oxyrrhis marina) as primary consumer to the food chain to establish the four-trophic-level food chain. This setup allowed us to investigate how nutrient-limitation effects change from one trophic level to another, and to investigate the performance of two components of our experimental food chains in different trophic positions. Stoichiometry and fatty acid profiles of the algae showed significant differences between the nutrient-depleted [no N and no P addition (-P), respectively] and the nutrient-replete (f/2) treatments. The differences in stoichiometry could be traced when O. marina was the first consumer. Copepods feeding on these flagellates were not affected by the nutritional imbalance of their prey in their stoichiometry, their respiration rates nor in their developmental rates. In contrast, when copepods were the primary consumer, those reared on the -P algae showed significantly higher respiration rates along with significantly lower developmental rates. In neither of our two experimental food chains did the signals from the base of the food chains travel up to jelly fish, our top predator.

Increased carbon dioxide availability alters phytoplankton stoichiometry and affects carbon cycling and growth of a marine planktonic herbivore

“…The copepodites investigated in this present study showed increasing respiration rates with an increase of carbon in their food. Higher body-specific respiration rates in juvenile stages suggest that juvenile copepods use respiration to dispose of excess C as CO 2 and regulate their homoeostasis (He and Wang 2008;Laspoumaderes et al 2010;Darchambeau et al 2003), a pattern which has been reported from other juvenile zooplankton species (Jensen and Hessen 2007;Malzahn et al 2010). Because larval and juvenile stages need high amounts of P to build the P-rich RNA necessary for high somatic growth (Sterner and Elser 2002;Malzahn and Boersma 2012), they are more likely to be P-limited and face an excess of carbon than the fully grown adult stages.…”

“…Both of these pathways have been proposed as stoichiometric regulation mechanisms in herbivorous consumers fed on algae with high carbon-tonutrient ratios (e.g. Darchambeau et al 2003;Jensen and Hessen 2007;Malzahn et al 2010;Saba et al 2009). Disposing of surplus C by respiration is a common mechanism, reported from a range of aquatic consumers including Daphnia, the copepod A. tonsa and the flagellate Oxyrrhis marina (Hantzsche and Boersma 2010; Malzahn Jensen and Hessen 2007).…”

“…In addition, several post-absorptive regulation mechanisms exist. Surplus carbon can be excreted through different mechanisms, ranging from increased activity (Plath and Boersma 2001) and respiration (Darchambeau et al 2003;Malzahn et al 2010) through changes in the digestion efficiency of carbon (DeMott and Tessier 2002). Whatever the mechanisms used, keeping homoeostasis and thus getting rid of excess carbon often comes at a cost to the herbivore and hence results in decreased growth and reproduction (Boersma 2000;Malzahn et al 2007).…”

“…These changes in carbon availability to the marine system are likely to have other potentially far-reaching impacts on the functioning of predator-prey interactions and may therefore affect the whole of the marine food web. Changes in food quality at the base of the food web affect primary consumers and thus propagate through the food web with potentially strong negative effects on the fitness and potentially the recruitment of higher trophic levels (Boersma et al 2009;Malzahn et al 2010;Schoo et al 2010Schoo et al , 2012. Higher availability of carbon and the subsequent changes in seawater nutrient composition, caused by the relatively lower availability of mineral nutrients compared to C, may also cause shifts in competitive interactions between algae (e.g.…”

Possible nutrient limiting factor in long term operation of closed aquatic ecosystem

“…In ecological research, the issue of nutrition quality and its effect on consumers has been the focus of attention for many years (Elser et al, 2000;Boersma et al, 2008;Malzahn et al, 2010). However, because most systems have been operated in an open condition, few studies have focused on closed ecological systems.…”