Essential Biomolecules in Food Webs

Abstract

We here review the ecological role of essential nutritional biomolecules [fatty acids (FA), amino acids (AA), sterols, vitamins] in aquatic and terrestrial food webs, encompassing the forces behind their environmental distribution. Across ecosystems, mutualistic relationships frequently ensure exchanges of vitamins between producer and demander, especially between B 12 and other B vitamins as well as the AA methionine. In contrast, FA, sterols and most AA are transferred up the food chain via classical predatorprey interactions, and therefore have good biomarker potential for trophic interactions. As biomass-flow depends on the absolute amounts of potential limiting resources, considering solely the relative share in the respective biochemical group may underor overestimate the availability to consumers. Moreover, if not accounted for, "hidden" trophic channels, such as gut symbionts as well as metabolic conversion of precursor molecules, can hamper food web analyses. Fundamental differences exist between aquatic and terrestrial ecosystems: Vitamin B 12 produced by ammonium oxidizing Archaea is essential to many aquatic algae, whereas terrestrial plants escaped this dependency by using B 12 independent enzymes. Long-chain ω3 polyunsaturated FA (LC-ω3PUFA) in aquatic systems mainly originate from planktonic algae, while in terrestrial systems, belowground invertebrates can well be a source, also supporting aboveground biota. Interlinks from terrestrial to aquatic ecosystems are of a biochemically totally different nature than vice versa. While biomass rich in proteins and LC-ω3PUFA is transferred to land, e.g., by trophic relationships, the link from terrestrial to aquatic ecosystems provides recalcitrant plant carbon, mainly devoid of essential nutrients, fuelling detrital food chains. Recent global changes influence food webs via altered input and transfer of essential biomolecules, but separating the effects of nutrients, CO 2 , and warming is not trivial. Current evolutionary concepts (e.g., Black Queen, relaxed selection) considering the costs of metabolic production partly explain food web dynamics, especially for vitamins, whereas adaptations to potential oxidative stress seem to be more important for LC-PUFA. Overall, the provision with essential biomolecules is precious for both heterotrophs and auxotrophs. These nutritional valuable molecules often are kept unaltered in consumer metabolism, including their stable isotope composition, offering a great advantage for their use as trophic markers.

Ocean-related global change alters lipid biomarker production in common marine phytoplankton

“…Alkenones were only observed in E. huxleyi in our study, consistent with previous results showing that these compounds were only synthesized by a few haptophytes including E. huxleyi (Volkman et al, 1980b;Volkman et al, 1998). The alkenone composition of E. huxleyi was characterized by the presence of four pairs of isomers, including eight alkenone compounds (Table S4) (Marlowe et al, 1984;Sachs et al, 2016;Riebesell et al, 2000). Moreover, higher abundance of several alkenone components have been also observed in some E. huxleyi strains under certain culture conditions, e.g., C37:4…”

“…Some of phytoplankton-produced biomolecules (biomarkers), functioning as indicators of nutritional food quality (Müller-Navarra, 2008) and tracers of organic matter sources (Volkman et al, 1998), have provided crucial insight into the trajectory of ecological responses to changing environment along food webs in the present-day ocean (Ruess and Müller-Navarra, 2019), and over geological time (Brocks et al, 2017).…”

“…Of all biomarkers, fatty acids (FAs), the basic constituents of most algal lipids, have received the most intense attention. Polyunsaturated fatty acids (PUFAs) are essential for many animals and have been applied as nutritional components to study trophic interactions (Kelly and Scheibling, 2012;Dalsgaard et al, 2003;Ruess and Müller-Navarra, 2019;Müller-Navarra et al, 2000;Brett and Müller-Navarra, 1997). The impact of environmental changes on phytoplankton FAs has been well studied, mostly with a focus on the effects of temperature and nutrient changes (reviewed by Guschina and Harwood, 2009;Hixson and Arts, 2016;Galloway and Winder, 2015), while the interplay between different environmental drivers has been recently tested (Bi et al, 2017(Bi et al, , 2018Bermúdez et al, 2015).…”

Increasing picocyanobacteria success in shelf waters contributes to long‐term food web degradation

“…Even though Synechococcus can reach near‐bloom concentrations in subsurface layers (Chl a ~ 1 mg/m 3 , Figure 3b), this biomass is of limited use for copepods as they cannot capture cells <5 µm efficiently (Kiørboe, 2008). Moreover, like all cyanobacteria, Synechococcus lack biomolecules such as omega‐3 polyunsaturated fatty acids and sterols (Jónasdóttir, 2019; Patil, Källqvist, Olsen, Vogt, & Gislrød, 2007; Ruess & Müller‐Navarra, 2019). These compounds are essential for both copepods and fish to acquire from their diet in order to sustain egg production and growth.…”

Global changes may be promoting a rise in select cyanobacteria in nutrient‐poor northern lakes

“…In freshwater ecosystems, cyanobacteria blooms are known to reduce resource quality of the food base (cf. Ruess & Müller-Navarra, 2019) Therefore, the increase in these genera could potentially be a short-lived artefact of the legacy effects of previous atmospheric changes. Conversely, future global changes promoting longer lake water retention times, higher pH and N limitation are anticipated to promote Dolichospermum (Sharma et al, 2019).…”