Tim M. Szewczyk1, Pippa J. Moore2, Dan A. Smale3, Thomas Adams4, and Michael T. Burrows1
1The Scottish Association for Marine Science, SAMS, Dunbeg, Oban, Argyll, PA37 1QA, UK
2Dove Marine Laboratory, School of Natural and Environmental Sciences, Newcastle University, Newcastle upon Tyne NE1 7RU, UK
3Marine Biological Association of the United Kingdom, The Laboratory, Citadel Hill, Plymouth PL1 2PB, UK
4Scottish Sea Farms, Stirling FK7 9JQ, UK
Laminaria hyperborea is a forest-forming kelp species in the North Atlantic that provides physical structure for diverse, productive ecosystems, with populations strongly affected by light availability, temperature, and storm-related disturbance. We constructed a stage-based, two-season model of L. hyperborea along the coast of the United Kingdom and Ireland to predict biomass across a range of depths, drawing on extensive surveys and data from the literature. Population dynamics were driven by wave exposure, historic winter storm intensity, and simulated interannual variation in temperature and depth-attenuated light intensity, with density-dependent competition for light and space. High biomass was predicted in shallow depths across the domain on suitable substrate, with populations extending deeper in the north and west. Interannual variability increased with wave exposure and decreased with mean biomass. Annual fluctuations in light and storm intensity produced opposing 3-year population oscillations persisting for up to a decade but diminishing sharply with depth. The largest environmental effects were from storms in shallow northwestern populations. Annual variation in temperature had minimal impact. Biomass was most sensitive to settlement and survival rates, with moderate sensitivity to the lamina erosion rate and form of density dependence, and negligible sensitivity to stipe and lamina growth rates. This model reproduced observed geographic patterns of L. hyperborea and highlights the need for a better understanding of mortality, particularly in the subcanopy, as well as recruitment and competition. While the most dramatic impacts of interannual environmental variability come from storms in the northwest of Scotland, populations recover quickly following major disturbances.