A simple growth model of Saccharina latissima cultivated in Scandinavia: Theoretical and practical implications

Our purpose was to construct the simplest possible, biologically-based model that could simulate the biomass growth from autumn to summer of Saccharina latissima cultivated on lines in Scandinavia. We developed the model based on a well-established framework for modelling terrestrial crops, using data from an experiment that we ran for one growing season with S. latissima cultivated on lines in Limfjorden, Denmark. The model was subsequently compared to two independent data sets obtained from previously published studies carried out in Denmark and Norway. Surprisingly, sea temperature was not needed as a driving variable to obtain a model as accurate as earlier models; global irradiation was the only environmental variable necessary to drive the model. Model outputs compared favourably to the independent Norwegian data set, less so to the independent Danish data set. In general, the predicted time trends of S. latissima biomass mimicked both the pattern and the magnitude of the observed biomass. Due to a lack of data, the model did not include the effects of sub-optimal levels of nutrients or salinity; however, thanks to the model's simplicity (it can be formulated in just one line) and its reliance upon basic biological principles, we expect that it can easily be re-calibrated to simulate growth also under sub-optimal conditions. Its plain formulation provides a readily available prediction of the biomass production to be expected from S. latissima cultivation. Moreover, the simplicity of the model makes it straightforward to incorporate as a component in more complex models of marine cropping systems. • Cultivated kelp can be modelled on the same principles as terrestrial crops. • Global irradiation, not temperature, was sufficient to model kelp growth. • A simple, one-line model was sufficient to provide an accurate model of kelp growth.