Rings of Power: How Key Biomolecules Could Tame Nutrient Cycles in Aquatic Food Webs

Global nutrient cycles are running dangerously hot. Humanity has already pushed nitrogen and phosphorus flows beyond the safe operating space of Earth’s planetary boundaries, and the consequences are visible in every eutrophic lake and algae-choked pond. A new conceptual paper published in Web Ecology by Koushik Roy and Jan Mraz of the University of South Bohemia argues that the scientific community has been tackling this crisis with the wrong toolkit. The problem, they contend, is not simply how much carbon, nitrogen, and phosphorus circulate through ecosystems, but in which biomolecular packages those elements arrive at the animals that sit above the primary producers. Their provocative answer borrows a metaphor from fantasy fiction: certain nutrient forms act like rings of power, orchestrating the fate of entire nutrient cycles in aquatic food webs.

For decades, ecologists have understood food webs through the lens of elemental ratios. Ecological stoichiometry, built on the famous Redfield ratio, treats carbon, nitrogen, and phosphorus as the fundamental currencies of life, tracking how these elements flow from algae to zooplankton to fish. Roy and Mraz acknowledge that this framework works reasonably well up to the level of primary producers. Plants, fungi, and protists genuinely do grow on free forms of elements, and the more nitrogen or phosphorus is fertilized into their environment, the more they grow. But the moment you move above the producers, the logic breaks down, and this is where the authors believe ecology has gone astray.

Animals, unlike plants, do not grow on free elemental nitrogen or phosphorus. They require biomolecules: proteins, lipids, carbohydrates, phospholipids, and specific amino acids. The evidence for this disconnect is striking. In fish, a meta-analysis of diet manipulation studies and field surveys found that the mean effect of dietary nitrogen-to-phosphorus ratios on excretion ratios was not significantly different from zero. This led researchers to hypothesize that future work must consider not just the ratios of nutrients in the diet but the molecular forms in which they are delivered. Roy and Mraz take this hypothesis to its logical conclusion: total nitrogen in seston or algae may be essentially meaningless for a zooplankter or a fish. What matters is the nitrogen bound in essential amino acids such as lysine and methionine, the carbon carried in digestible non-protein fractions like starch, and the phosphorus packaged in phospholipids rather than in apatite or phytate forms.

The authors illustrate this with concrete examples from fish nutrition. Supply the same amount of nitrogen to fish mainly through non-essential amino acids, and growth is modest; supply it through essential amino acids, and growth improves markedly. Deliver carbon through a high-protein diet versus non-protein energy fractions on an isoenergetic basis, and the non-protein route yields better growth. Phosphorus storage in fish remains low whenever key biomolecular packages are in short supply, regardless of how much total phosphorus the diet contains. These interactions, well documented in animal nutrition literature, are systematically overlooked in food web ecology, where carbon, nitrogen, and phosphorus are mathematically treated as if every atom were equivalent.

Why does this matter so much for animals? The answer lies in evolutionary physiology. Consumers above the primary producers have lost roughly half of their amino acid synthesis capabilities, including the ability to make essential amino acids. Unlike plants, animals cannot use photonic energy to synthesize biomass from absorbed elements; they must first catabolize energy-rich molecules to fuel the synthesis and storage of new matter. Their bodies are governed by homeostatic control, meaning they cannot simply mirror the elemental composition of their food. The fates of carbon, nitrogen, and phosphorus inside an animal, whether retained in biomass or excreted back into the environment, are dictated by a handful of key biomolecules whose required proportions shift relative to the energy available from non-key molecules.

This is where the rings of power concept acquires its practical teeth. When surplus energy comes from dietary non-key biomolecules such as starch, glycogen, saturated fats, or non-essential amino acids, the animal’s requirement for expensive key biomolecules drops, and more dietary nitrogen and phosphorus remain locked in body tissue. When energy from non-key biomolecules is inadequate, the animal is forced to burn its own key biomolecules for fuel, destroying them and releasing their nitrogen and phosphorus back into the water. In the authors’ framing, sufficient rings of power abolish the nutrient-energy transfer barriers between food and body and suppress nutrient leakage from consumers. When the rings are missing, ecosystems degrade into a soup of free nutrients: primary productivity overshoots, secondary and tertiary productivity stall, and the chain of trophic transfer efficiency breaks down entirely.

The concept has immediate relevance for one of the most stubborn water quality problems on the planet. Nutrients from human settlements, agricultural runoff, and farming accumulate in standing water bodies like the drain of a shower sink, driving harmful algal blooms and hypoxic dead zones. Roy and Mraz point out that specific rings of power, such as the amino acid lysine, saturated fatty acids, and the carbohydrate starch, go missing from pond plankton over the vegetative season or are absent throughout it. Their absence impedes the assimilation of nutrients into the bodies of aquatic consumers, leaving nitrogen and phosphorus freely available in the water column. Fish excretion alone can support a significant proportion of lake primary productivity, so the nutritional state of fish stocks directly modulates how much phosphorus recycles versus how much stays locked in biomass.

The proposed solution is audacious: design stoichiometrically corrective seasonal feeds spiked with the rings of power and deploy them in hypertrophic inland water bodies to convert pollution into harvestable biomass. In spring and autumn, digestible non-protein energy feeds would tip the balance; in summer, feeds balanced in essential amino acids and non-protein energy would sustain it. Well-fed fish with high metabolic satiety and gut fullness would graze less actively on zooplankton, allowing the planktonic food web to keep carbon, nitrogen, and phosphorus sequestered. Fish would additionally absorb orthophosphate directly from the water through their integuments, adding a second pathway for nutrient removal. Periodic stocking and harvesting of fish stocks would then physically crop the anthropogenic nutrients out of the ecosystem, transforming eutrophic ponds from points of pollution into regenerative solutions.

This approach deliberately exploits what the authors call a natural flaw. Natural food webs help digest nutrients, but metabolic assimilation is poorly constrained by stoichiometric errors and consumer homeostasis when diets are imbalanced. In nature, this is a deliberate error that keeps primary productivity running on the free nutrients leaked by consumers. Animal nutritionists have spent decades correcting precisely these flaws in commercial production systems, achieving far higher nutrient use efficiencies in poultry, pigs, and fish than were possible in the past. Roy and Mraz argue that this expertise, honed by commercial interest and physiological understanding, is exactly what ecology has been missing, and they call for the establishment of nutritional ecology as a formal field within educational and research organizations, with animal nutritionists trained and tasked to work on ecological applications.

The rings of power concept is, at this stage, a conceptual framework rather than a proven remedy, and the authors are candid about its speculative nature. Yet it arrives at a moment when conventional remediation, chemical treatments, and algae- or microbe-based biotechnologies struggle against the sheer scale of global eutrophication. If even a fraction of the framework holds under field testing, the implications ripple outward: pond aquaculture could become a nutrient-capture industry, fishponds across temperate Europe could double as water purification infrastructure, and the stubborn boundary between the science of what animals eat and the science of how ecosystems work might finally be bridged. Sometimes, the authors suggest, the most powerful tool for saving an ecosystem is not a new chemical or a new organism, but a better understanding of the molecular packages in which nature’s elements already travel.

Subject of Research: Biomolecular control of nutrient cycling in aquatic food webs and regenerative aquaculture

Article Title: The Rings of Power: managing nutrient cycles in aquatic food webs above and beyond primary producers

Article References: Roy, K., & Mraz, J. (2026). The Rings of Power: managing nutrient cycles in aquatic food webs above and beyond primary producers. Web Ecology, 26(1), 27-33. https://doi.org/10.5194/we-26-27-2026

Image Credits: AI Generated

DOI: 10.5194/we-26-27-2026

Keywords: nutrient cycles, aquatic food webs, ecological stoichiometry, eutrophication, fish nutrition, essential amino acids, phosphorus, nitrogen, zooplankton, aquaculture, biomolecules, water quality