Fronds to forests: Individual-based and whole-forest models of kelp

Harvesting of seaweeds for biofuel, fertiliser, and extraction of chemicals for human and animal food products, and pharmaceuticals, is a significant industry in some countries especially the Far East1. In the northeast Atlantic region, significant harvesting involving dedicated vessels occurs only in France and Norway. The annual Norwegian harvest is more than 100,000 tonnes. The biomass of kelp (mainly Laminaria hyperborea) in Scottish waters is estimated to be in excess of 20 million tonnes2, and a 10,000-15,000 tonne per annum harvesting industry developed in the Western Isles during the 1970's-1990's. However, the current harvesting is confined to a small number of hand-harvesting businesses producing speciality products, and recent proposals for mechanical harvesting have been rejected by the Scottish Government pending a thorough review.
Opposition to mechanical harvesting of kelp at sites in Scotland appears to be motivated more by a precautionary approach, and not based on any specific scientific evidence of large scale adverse consequences, at least from the scale of harvesting that is envisaged. In fact, although there is ample experience-based knowledge on effective harvesting strategies from French and Norwegian experiences, scientific understanding of kelp forest dynamics is markedly lacking. Kelp are relatively long-lived (up to 10 years depending on species) physiologically complex plants, able to store significant reserves of nitrogen, and excrete quantities of polysaccharides into the environment. Forests provide a dense habitat for a wide range of invertebrate and vertebrate species, and forest dynamics depend on a range of environmental factors such as turbidity, temperature and wave exposure, and density-dependent regulatory process such as inter-generational competition for space (settling spores require a secure surface for holdfast development), and self-shading competition for light. These density dependent processes are exactly the ones that may mitigate or accentuate any effects of harvesting on the forests.
In this project we will develop mathematical models of kelp forest dynamics appropriate to Scottish waters that can then be used to explore the consequences of natural variability and harvesting on forest biomass and regeneration. We will approach the problem from two directions - using models of whole-forest biomass and properties, and individual-based models of interacting plants. The few models of kelp dynamics that exist in the literature3,4 generally model the development (growth and survival ) of individual plants, and then assume that this is synonymous with forest development. However, this is not necessarily the case.
The task of the PhD project will be to:
-Develop, test and parameterise both the forest and individual-based models for a range of well studies sites around Scotland, starting with the legacy of historical data from Loch Creran5.
-Conduct model experiments to determine the extent, and under what conditions and parameter values, the whole-forest model is able to simulate the behaviour of the individual-based models.
-Conduct experiments with the models to determine the optimum harvesting strategy to ensure sustainable forest biomass and structure into the future
1Capuzzo, E. and McKie, T. (2016). Seaweed in the UK and abroad - status, products, limitations, gaps and Cefas role. Cefas contract report FC002I. 78pp.
2Burrows et al. (2018) Wild Seaweed Harvesting as a Diversification Opportunity for Fishermen. A report by SRSL for HIE, pp. 171
3Aldridge, J., van de Molen, J. and Forster, R. (2012). Wider ecological implications of Macroalgae cultivation. The Crown Estate, 95 pp.
4Broch, O.J. and Slagstad, D. (2012). Modelling seasonal growth and composition of the kelp Saccharina latissimi. J. Appl. Phycol. 24, 759-776.
5Johnston, C.S., Jones, R.G. and Hunt, R.D. (1977). A seasonal carbon budget for a laminarian population in a Scottish sea-loch. Helgolander Wiss.