Temperature-Driven Biochemical and Physiological Responses in the Arctic Diatom species Melosira arctica and Thalassiosira nordenskioeldii
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Abstract:
Authors: Carla Marlene Pein (GEOMAR), Alexandra Kraberg (AWI), Kevin Becker (University of Bremen), Anja Engel (GEOMAR)
Increasing temperatures in the Arctic Ocean represent one of the most pronounced manifestations of ongoing climate change, imposing substantial stress on marine ecosystems. Diatoms contribute approximately 40% of global marine primary productivity and form the foundation of marine food webs, thereby playing a critical role in nutrient cycling and carbon sequestration. Phytoplankton productivity is strongly influenced by the abiotic environment, particularly temperature, which is controlling physiological processes and rates, biochemical composition, and, in consequence, community structure. The objective of this study is to investigate the relationship between thermal performance and the biochemical composition of diatoms. Specifically, we aim to identify biochemical responses to warming that may serve as indicators of biodiversity shifts.
We investigated the effects of temperature on the physiology and biochemical composition of the Arctic diatom species Melosira arctica and Thalassiosira nordenskioeldii, using batch culture experiments. Cultures were grown at five temperature treatments (0°C, 3°C, 6°C, 9°C, and 12°C), representing ambient conditions and projected warming scenarios. Samples were collected during both the exponential and stationary growth phases. Cell abundance was determined by microscopic counts, while photosynthetic performance was evaluated using single-turnover active fluorometry. To characterize changes in biochemical composition, we measured particulate organic carbon (POC) and quantified the concentration and composition of carbohydrates, amino acids, and lipids.
Our results reveal pronounced species-specific responses to temperature, with both species exhibiting maximum growth rates at approximately 11°C, indicating they naturally grow below their thermal optimum. However, increases in growth rates were accompanied by substantial shifts in biochemical composition. A pronounced decline in glucose content was observed in T. nordenskioeldii with increasing temperature, whereas M. arctica exhibited only minor biochemical changes in POC composition. Glucose represented the dominant carbohydrate at lower temperatures, but its concentration decreased progressively with warming in T. nordenskioeldii, becoming undetectable at 12°C. This indicates a warming-induced reallocation of carbon within the cell, suggesting that the maintenance of high growth rates under warming conditions may occur at the expense of key biochemical traits linked to nutritional quality. This may alter the transfer efficiency and availability of energy and nutrients to higher trophic levels, as well as carbon cycling.
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