The role of cost–benefit analysis in models of phytoplankton growth and acclimation

Background: A key current issue in pelagic ecosystem modelling is obtaining better representations of the growth of phytoplankton so as to increase our understanding of the links between climate change and ocean biogeochemistry. Aims: Here we explore the use of cost-benefit analysis within the context of assessing the optimal distribution of resources for maximizing phytoplankton growth. Methods: We focus on capital and running costs by revisiting some of John Raven's cost-benefit analyses of chloroplast structure/function relations. Then, we describe a general framework for application of cost-benefit considerations in models of phytoplankton growth. Conclusions: Key to applying optimality criteria to phytoplankton growth models is quantifying the costs and benefits of alternative acclimation strategies. Costs include (1) capital costs of the structural and functional components of the cell, (2) running costs of CO2 fixation, nutrient acquisition, biosynthesis and repair, (3) opportunity costs for exploiting variability in the environment, and (4) taxes imposed by losses associated with transport to unfavourable environments, grazers and parasites. On short timescales of phytoplankton blooms, benefits can be assessed through influences on net growth rate, which can be increased by maximising resource gain (r-strategy) or minimizing losses (K-strategy). On longer timescales from years to millennia, the benefit is survival.