Seasonal kelp primary production at a rocky shore site: Integrating physiology and biochemistry into ecological modelling

• Applicant: Professor Dr. Ulf Karsten, since 4/2019
• Subject Area: Ecology and Biodiversity of Plants and Ecosystems ; Plant Physiology
• Term: from 2018 to 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 407670545

• Final Report Year: 2024

Final Report Abstract

The project represents a first seasonal photophysiological study of the kelp Laminaria hyperborea. We successfully applied a method to measure oxygen production in macroalgae and measured the photosynthesis curves as a function of light in L. hyperborea under continuous conditions. With the proven setup we measured oxygen production in algae from different depths, along the thallus gradient and in different temperature scenarios (ambient and Δ+4°C) during all four seasons. The results revealed a high photoacclimation potential along the depth gradient, e.g. less light was required to saturate photosynthesis in algae from deeper depth. Along the thallus gradient, oxygen production only showed differences when normalized to fresh mass and not when normalized to surface area. We therefore strongly recommend normalization to surface area in order to exclude differences due to the mass of the middle, photosynthetically inactive cell layers. We investigated photosynthetic performance in terms of O2 release and C-fixation and determined seasonal photosynthetic quotients (PQs). While oxygen production was significantly higher in high-light seasons of spring and summer, only a slight seasonal dependence was observed for C-fixation with the same tendency as for oxygen. PQ values were highest in summer. In addition to the seasonal measurements, cover-biomass relationships were also recorded during the summer campaign. The correlation made it possible to convert previous cover data into biomass information. The leaf area index data was used for our net primary production (NPP) modelling. The warming scenario, in which all measurements were carried out in comparison to the ambient temperature, had a stimulating effect and intensified the seasonal pattern. In winter and summer, NPP rates were comparable between the warming scenario and ambient temperature, but in spring, the increased temperature significantly stimulated the NPP rates, while in autumn, the NPP rates were negatively influenced under warming conditions. This once again emphasises the importance of seasonal studies, as the effects of rising water temperatures can be completely different from season to season. We also calculated a yearround carbon budget to gain a better understanding of the distribution of fixed carbon in the different cellular processes. The typical seasonality was also evident here, with growth maxima in spring and winter, while the storage of reserve substances tended to take place in spring and summer. Finally, we started to develop a dynamic primary production model. Since L. hyperborea does not grow in all seasons, the existing growth-based model cannot adequately represent the data adequately in all seasons, and further adjustments are needed for this implementation, which will be carried out beyond this project.

Publications

• Model simulation of seasonal growth of Fucus vesiculosus in its benthic community. Limnology and Oceanography: Methods, 18(3), 89-115.
  Graiff, Angelika; Karsten, Ulf; Radtke, Hagen; Wahl, Martin & Eggert, Anja
  
• 12th International Phycological Congress; First step to a dynamic physiological kelp primary production model Mar. 22-26, 2021, Chile, virtual Oral Poster Presentation
  Kiara Franke, Angelika Graiff & Inka Bartsch
  
• Antioxidative Properties of Baltic Sea Keystone Macroalgae (Fucus vesiculosus, Phaeophyceae) under Ocean Warming and Acidification in a Seasonally Varying Environment. Biology, 10(12), 1330.
  Graiff, Angelika & Karsten, Ulf
  
• Looks can be deceiving: contrasting temperature characteristics of two morphologically similar kelp species co-occurring in the Arctic. Botanica Marina, 64(3), 163-175.
  Franke, Kiara; Liesner, Daniel; Heesch, Svenja & Bartsch, Inka
  
• Seasonal Photophysiological Performance of Adult Western Baltic Fucus vesiculosus (Phaeophyceae) Under Ocean Warming and Acidification. Frontiers in Marine Science, 8.
  Graiff, Angelika; Bartsch, Inka; Glaser, Karin & Karsten, Ulf
  
• ICYMARE - International Conference for Young Marine Researcher; The Helgoland kelp forest - First estimation of summer productivity Sep. 13-16, 2022, Bremerhaven, Germany Oral Presentation
  Kiara Franke, Lisa Matthes, Angelika Graiff, Ulf Karsten & Inka Bartsch
  
• Photosynthetic performance, growth, pigment content, and photoprotective compounds of the mangrove macroalgae Bostrychia calliptera and Bostrychia montagnei (Rhodophyta) under light stress. Frontiers in Marine Science, 9.
  Borburema, Henrique D. S.; Graiff, Angelika; Marinho-Soriano, Eliane & Karsten, Ulf
  
• 20th Scientific Conference of the Section Phycology; Seasonal variability in the photosynthetic performance of a kelp species in the face of ocean warming Mar. 12-15, 2023, Jena, Germany Oral Presentation
  Kiara Franke, Angelika Graiff, Inka Bartsch & Ulf Karsten
  
• 8th European Phycological Congress; Seasonal varying photosynthetic quotients and the consequences for the annual net primary production of a kelp species Aug. 20-26, 2023, Brest, France Oral Presentation
  Kiara Franke, Inka Bartsch, Ulf Karsten & Angelika Graiff
  
• The challenge of estimating kelp production in a turbid marine environment. Journal of Phycology, 59(3), 518-537.
  Franke, Kiara; Matthes, Lisa C.; Graiff, Angelika; Karsten, Ulf & Bartsch, Inka
  
• Seasonality influences the effect of warming on kelp photosynthesis. Marine Ecology Progress Series, 739, 15-29.
  Franke, K.; Bartsch, I.; Karsten, U. & Graiff, A.