Ocean acidification impairs seagrass performance under thermal stress in shallow and deep water

Highlights

• Shallow and deep plants were exposed to ocean acidification and thermal stress;
• Plants were unaffected by ocean acidification when not exposed to thermal stress;
• Ocean acidification reduced plant performance under thermal stress;
• Deep plants showed higher levels of heat stress at genetic and physiological levels;
• Warming may play a key role in structuring future seagrass meadows.

Abstract

Despite the effects of ocean acidification (OA) on seagrasses have been widely investigated, predictions of seagrass performance under future climates need to consider multiple environmental factors. Here, we performed a mesocosm study to assess the effects of OA on shallow and deep Posidonia oceanica plants. The experiment was run in 2021 and repeated in 2022, a year characterized by a prolonged warm water event, to test how the effects of OA on plants are modulated by thermal stress. The response of P. oceanica to experimental conditions was investigated at different levels of biological organization. Under average seawater temperature, there were no effects of OA in both shallow and deep plants, indicating that P. oceanica is not limited by current inorganic carbon concentration, regardless of light availability. In contrast, under thermal stress, exposure of plants to OA increased lipid peroxidation and decreased photosynthetic performance, with deep plants displaying higher levels of heat stress, as indicated by the over-expression of stress-related genes and the activation of antioxidant systems. In addition, warming reduced plant growth, regardless of seawater CO₂ and light levels, suggesting that thermal stress may play a fundamental role in the future development of seagrass meadows. Our results suggest that OA may exacerbate the negative effects of future warming on seagrasses.

Ravaglioli C., De Marchi L., Anselmi S., Dattolo E., Fontanini D., Pretti C., Procaccini G., Rilov G., Renzi M., Silverman J. & Bulleri F., 2024. Ocean acidification impairs seagrass performance under thermal stress in shallow and deep water. Environmental Research 241: 117629. doi: 10.1016/j.envres.2023.117629. Article.

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