Optimality-based modelling of marine plankton processes.

Pahlow, Markus (2016) Optimality-based modelling of marine plankton processes. (Professorial dissertation), Christian-Albrechts-Universität Kiel, Kiel, Germany, 192 pp.

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Abstract

This thesis describes optimality-based modelling approaches from plankton organisms to communities. Physiological process descriptions of phytoplankton optimal growth regulation and zooplankton optimal foraging behaviour have been derived from energetic and allocation trade-offs representing physiological and biochemical limits of growth.
Optimality-based models have been shown to offer a large potential for generalisation and reduce the number of free parameters compared to more mechanistic modelling approaches. This is achieved by replacing specifically parametrised relations with closures obtained from generic trade-offs restricting the possibilities to maximise a goal function, normally taken to be net relative growth rate. Energy and cellular resource requirements of inorganic nutrient and carbon acquisition govern trade-offs involved in phytoplankton growth. The optimality-based phytoplankton growth models introduced here demonstrate the potential for upscaling and generalisation. This approach started by combining light-acclimation with dynamic nitrogen:carbon quotas and was subsequently extended to cover phosphorus and nitrogen fixation. The resulting formulations are currently among the most general descriptions of dynamic and steady-state phytoplankton growth and require very little parameter tuning to achieve this generality. Optimal resource allocation can also explain the shape to Droop’s famous cell-quota phytoplankton growth model. The energy balance of ingestion, respiration, and excretion determines foraging activity in an optimal current-feeding model. This model can be viewed as a generalisation of previous optimal-foraging descriptions. A major departure from other optimal-foraging formulations is the use of a linear relation between the cost of foraging and foraging activity. The previously prevailing assumption of a quadratic relation was based on the relation between intensity of the feeding current and energy dissipation, which, however, was later shown to be an insignificant contribution to the overall cost of foraging. The linear relation is in line with observations and, in contrast to the quadratic relation, implies significant feeding thresholds. Similar to the optimal phytoplankton growth models, the optimal current-feeding model has demonstrated potential for generalisation and was successfully applied to a wide range of organisms, from protozoans to mussels. In spite of its name, it can as well be applied to other foraging strategies, e.g., cruise- and filter-feeding. Optimality-based formulations of phytoplankton, bacteria, and zooplankton growth were combined with adaptive switching in zooplankton to construct a plankton ecosystem model for the North Atlantic. With the help of a simplified version replacing the adaptive switching dynamics with a steady-state approximation, it was shown that adaptive dynamics did improve the portability of the model: With a single parameter set applied to three locations from the subtropical to the subpolar North Atlantic, the adaptive dynamics resulted in a much better model performance than the simplified model. Their potential for generalisation across species and even larger taxonomic levels makes optimality-based approaches appear as promising candidates for upscaling from the behaviour of individuals to communities. A preliminary example demonstrating the existence of an optimal level of intraspecific diversity implies that optimality-based models might shed new light on the generation of diversity.

Document Type: Thesis (Professorial dissertation)
Research affiliation: OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-BM Biogeochemical Modeling
Date Deposited: 10 Apr 2017 11:14
Last Modified: 02 Nov 2022 09:46
URI: https://oceanrep.geomar.de/id/eprint/37504

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