Willim, Jana (2023) Long-term acclimation and metabolic responses of eelgrass (Zostera marina) clones to a summer heat wave. (Master thesis), Christian-Albrechts-Universität zu Kiel, Kiel, Germany, 37 pp.

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Abstract

Ongoing ocean warming driven by climate change is increasing stress on many coastal ecosystems, including seagrass meadows. Like other seagrass species, Zostera marina has been shown to be vulnerable to rising sea temperatures, resulting in growth reduction, reduced photosynthesis as well as die-offs of shoots during periods of summer heat waves. For northern temperate populations, a critical threshold temperature has been identified at approximately 25°C. The underlying physiological processes are largely unresolved. While assessments of photosynthesis, growth, and survival provide useful information about plant performance, metabolomics offers a complementary approach to understanding the physiological states of plants under abiotic stress. Here, I used a long-term heat wave experiment with Zostera marina kept in large indoor wave tanks (Zosteratron) over 3 consecutive years. Half of the treatments received three summer heat waves of 26°C, while a second treatment group was only challenged once in the third year. The experiment included three wild-collected clones and was fully crossed. I examined both the primary response of the metabolome of three different clones to an acute heat wave, as well as potential acclimation from the two preceding years. I found a small but detectable impact of the heat treatment on the metabolome three weeks after the heat wave. However, no evidence of an acclimation process was observed. The metabolome of Zostera marina leaves was found to be mainly affected by clone affiliation. Notably, one clone exhibited significantly higher quantities of targeted metabolites and the most robust growth rates compared to the red and yellow clones. Metabolomics provided a detailed insight into the phenotypic response of Zostera marina leaves to heat wave treatment and clone affiliation. The results suggest responses to environmental stressors in terms of their metabolomic reactions may be very clone-specific in Zostera marina. This finding emphasizes the importance of genotype selection in the restoration process. Assisted evolution strategies are already discussed in order to enhance the thermal resilience of coral reefs and could also be implemented in seagrass meadow restoration in the future.

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