Seebass, Katja (2023) Sea star at the limit: Short-term heat stress affects coelomocytes and cellular metabolism in the common sea star Asterias rubens. (Master thesis), Christian-Albrechts-Universität zu Kiel, Kiel, Germany, 52 pp.

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Abstract

This study investigated the upper thermal threshold of A. rubens from the western Baltic Sea, a key predator crucial in maintaining benthic ecosystem balance. Further, the objective was to assess the impact of intense thermal stress on the immune capacity and energy metabolism of A. rubens. Under controlled laboratory conditions, individuals were exposed to temperatures ranging from 19°C to 23.5°C, with temperatures above 22°C deemed stressful. The immune system response was quantified by analyzing immune cell abundance and activity through flow cytometry and an in- vitro phagocytosis assay. Energy metabolism was evaluated using ¹H-NMR spectroscopy. Exposure to 23.5°C led to mortalities in sea stars within 13.5 to 18.5 days. These findings suggest that 23.5°C might represent the thermal tolerance limit of A. rubens. At temperatures between 22-23.5°C, energy metabolism was com- promised, indicating highly stressed individuals. Significant inter-individual variability in immune cell counts and activity could either have masked treatment effects or suggest a stabilized
immune response in A. rubens under extreme thermal conditions. Further studies using refined methodologies are rec- ommended to confirm these findings especially as predictions of temperature rise suggest potential challenges for A. rubens in the future.

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