Droop models of nutrient–plankton interaction with intratrophic predation

Droop models of nutrient–phytoplankton–zooplankton interaction with intratrophic predation of zooplankton are introduced and investigated. The models proposed in this study are open ecosystems which include both a constant and a periodic input nutrient models. A simple stochastic model mimics a randomly varying nutrient input is also presented. For the deterministic models it is shown analytically that intratrophic predation has no effect on the global asymptotic dynamics of the systems if either one of the populations has a negative growth rate. Numerical simulations are also used to investigate the effects of intratrophic predation. Unlike the deterministic models for which both populations can coexist with each other if populations’ net growth rates are positive, plankton populations can become extinct if the input nutrient concentration is varied randomly

Model based analysis of plankton responses to variations in nutrient stoichiometry in oxygen minimum zones

The present study aims to investigate the effect of nitrogen (N) and phosphorus (P) cycling on elemental stoichiometry of marine plankton across different trophic ecosystem levels in the Eastern Tropical South Pacific boundary system of Peru. The Peruvian upwelling region is one of the most productive upwelling systems of the world. However, the upwelling area is accompanied by oxygen deficient water masses, known as the Peruvian oxygen minimum zone (OMZs). Oxygen deficient water masses influence marine N and P inventories, may lead to shifts in the community composition (e.g., fish) and affect marine environments and humans. The present study suggests that microbial processes can contribute significantly to the food web dynamics and the N and P cycles in the Peruvian Upwelling region. Furthermore, this modeling study will permit to investigate the intimate interplay of marine biogeochemical cycles by observing changes of the N and P stoichiometry, at the organisms’ level throughout the planktonic food web. Moreover, the sixth chapter suggests the implementation of the planktonic lipid metabolism in physiological process models as a next step, in order to investigate more closely the effects of environmental changes on food quality for consumers of the planktonic food web

Model basierte Analyse von planktischen Reaktionen auf Variationen der Nährstoffstöchiometrie in Sauerstoffminimumzonen

The present study aims to investigate the effect of nitrogen (N) and phosphorus (P) cycling on elemental stoichiometry of marine plankton across different trophic ecosystem levels in the Eastern Tropical South Pacific boundary system of Peru. The Peruvian upwelling region is one of the most productive upwelling systems of the world. However, the upwelling area is accompanied by oxygen deficient water masses, known as the Peruvian oxygen minimum zone (OMZs). Oxygen deficient water masses influence marine N and P inventories, may lead to shifts in the community composition (e.g., fish) and affect marine environments and humans. The present study suggests that microbial processes can contribute significantly to the food web dynamics and the N and P cycles in the Peruvian Upwelling region. Furthermore, this modeling study will permit to investigate the intimate interplay of marine biogeochemical cycles by observing changes of the N and P stoichiometry, at the organisms’ level throughout the planktonic food web. Moreover, the sixth chapter suggests the implementation of the planktonic lipid metabolism in physiological process models as a next step, in order to investigate more closely the effects of environmental changes on food quality for consumers of the planktonic food web.Die hier vorgelegte Studie untersucht Auswirkungen von Stickstoff (N) und Phosphor (P) auf die Nährstoffstöchiometrie von marinem Plankton über mehrere trophische Ökosystemebenen in den Küstenauftriebsgebieten des östlichen tropischen Südpazifiks vor Peru. Das Auftriebsgebiet vor Peru ist eine der produktivsten Auftriebzonen der Erde. Jedoch ist diese Auftriebszone von sauerstoffarmen Wassermassen begleitet, welche auch als Sauerstoff-Minimum-Zone bezeichnet werden (SMZ). Wassermassen mit geringer Sauerstoffsättigung beeinflussen Nährstoffspeicher und können möglicherweise zu Verschiebungen der Gemeinschaftsstruktur (z. Bsp., von Fischen) führen und somit die marinen Lebensräume und den Menschen beeinflussen. Die vorgelegte Studie besagt, dass mikrobiologische Prozesse ausschlaggebend an der Nahrungsnetzdynamik und dem Stickstoff- und Phosphatkreislauf des Peruvianischen Auftriebssystems beteiligt sind. Die Modellierung ermöglicht die sukzessive Beobachtung von Wechselwirkungen zwischen den marinbiogeochemischen Kreisläufen und den Veränderungen der N- und P-Stöchiometrie auf Organismusebene über das planktische Nahrungsnetz. Des Weiteren weist diese Studie als nächsten Schritt im sechsten Kapitel auf die Einführung des planktischen Fettstoffwechsels in physiologischen Prozessmodellen hin, um die Auswirkungen von Umweltveränderungen auf Nahrungsqualität der Konsumenten im planktischen Nahrungsnetz näher zu untersuchen