C and P in aquatic food chain: A review on C:P stoichiometry and PUFA regulation

Abstract

Key-words:aquatic ecosystem, grazing food chain, microbial loop, PUFA, stoichiometry, homeostasis Carbon (C) and phosphorous (P) regulation in aquatic food chains are transferred from lower to upper trophic levels primarily as polyunsaturated fatty acids (PUFAs) and C:P stoichiometry. The majority of C is transferred through algal based pathway. Microbial loop, though optionally contributes to C transfer, highly constrained by P limitation and bacterial predator type. Lack of essential PUFAs in bacteria is also responsible for its low trophic transfer of C. The seston size and algal taxonomic variations directly affect herbivore through P-dependent food quality and de novo synthesis of PUFAs. Change in algal community over a gradient could therefore determine C transfer. Feeding nature (herbivorous or carnivorous) and predator sizes also regulate transfer efficiency of C and P to upper trophic levels. As trophic levels move up, P-limitation becomes higher compared to autotrophs. For Daphnia, as mostly studied aquatic herbivore member, P limitation becomes critical at C:P > 300 indicating excess C is not always invited under P-deficient situations. However, as a part of homeostasis mechanism for trophic upgrading, conversion of algal-zooplankton interface from qualitative to quantitative could minimize such critical C:P regulation at higher trophic levels. Protists, in turn, with high clearance rate by zooplankton predator could also compensate qualitative effect. RÉSUMÉC et P dans les chaînes alimentaires aquatiques : une revue sur la stoechimétrie C:P et la régulation par les PUFA Les régulations par carbone (C) et phosphore (P) dans les chaînes trophiques aquatiques sont transférées des niveaux trophiques inférieurs vers les supérieurs au travers des acides gras polyinsaturés (PUFAs) et du rapport stoechiométrique C:P. La majorité du C est transférée par la voie reposant sur les algues. La boucle microbienne, bien que contribuant au transfert du C, est très contrainte par la limitation en P et la prédation. Un manque de PUFAs essentiels est également responsable de ce faible transfert du C. La taille du seston et les variations taxonomiques des algues affectent directement les herbivores au travers de la qualité nutritionnelle dépendante du P et de la synthèse de novo de PUFAs. Le type de nourriture (herbivorie ou carnivorie) et les tailles de prédateurs régulent aussi l'efficacité du transfert de C et P vers les niveaux trophiques supérieurs. La limitation par P devient plus importante dans les niveaux trophiques supérieurs. Pour Daphnia, comme pour beaucoup d'organismes herbivores étudiés, la limitation par P devient cruciale quand C:P > 300, indiquant un excès de C pas toujours dû à des situations de déficience en P. Toutefois, comme part du mécanisme d'homéo-stasie pour le « trophic upgrading », le passage de l'interface algue-zooplancton de qualitatif à quantitatif peut atténuer la régulation critique C:P aux niveaux trophiques supérieurs. Les protistes, avec un taux de prédation par le zooplanct...

The potential of periphyton-based cage culture of Nile tilapia in a Brazilian reservoir

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When is an herbivore not an herbivore? Detritivory facilitates herbivory in a freshwater system

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Impacts of inorganic nutrients on the physiology of a mixoplanktonic ciliate and its cryptophyte prey

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