Trophic Transfer Efficiency in the Pelagic Food Chain: A Carbon Odyssey

Energy transfer in the ocean is the journey of energy through oceans food webs. Trophic transfer efficiency is the efficiency with which energy flows from one level in the food chain to the next through predation. Photosynthetic plankton are at the base of the marine food web and fuel with energy the entire marine ecosystem, by converting carbon dioxide to organic carbon and incorporating it to their bodies. Carbon is transferred to larger plankton through predation, following the paradigm that big eats small, before it reaches small fish. Trophic transfer efficiency regulates ecosystem services, such as fish production and carbon export, therefore estimating trophic efficiency can help us understand ecosystem services, and how they can be altered under climate change.

In this thesis, we introduce the NUM library, a computational framework of the NUM model that operates in three environments: a chemostat, a water column and the global ocean and can be utilized as a practical tool for marine ecology studies. The Nutrient-Unicellular-Multicellular plankton model is a trait-based model, that uses size as the master trait that shapes size structure of plankton community, the strategy acquisition of nutrition by unicellular plankton, and predator-prey interactions across unicellular and multicellular plankton.

In the first manuscript we develop an algorithm for downregulation, a process that optimizes the resource uptakes of a plankton organisms in response to environmental shifts. In the second manuscript, we present the NUM library enhanced with the inclusion of diatoms, and evaluate its performance, showing it can capture general global patterns. Last, in the third manuscript we define a novel metric of trophic transfer efficiency from phytoplankton to fish, and use the NUM library to map global trophic efficiency. We infer that the NUM library provides the infrastructure to estimate trophic transfer efficiency on a global scale and uncover the underlying mechanisms that form it.