Effects of an experimental heatwave on a plankton community from a Mediterranean artificial lake.

Global warming is profoundly altering aquatic ecosystems, with climate models predicting a significant increase in the frequency, duration, and intensity of heatwaves. These prolonged periods of unusually high temperatures are becoming more common globally, and especially in the Mediterranean, recognized as one of the most vulnerable areas. Artificial lakes, crucial for essential ecosystem services, are particularly sensitive to these changes. This scientific proposal investigates the impact of a simulated summer heatwave on a natural plankton community collected from Bidighinzu Lake, an artificial lake located in Sardinia (Western Mediterranean). In July 2024, we incubated a multi-trophic level plankton community (including picoplankton, nanoplankton, microplankton and mesoplankton) in laboratory for 15 days, applying two combined treatments in triplicates: a + 5°C water temperature increase and the presence/absence of mesozooplankton as apical predator. Water samples were collected every 3-4 days for analyses of algal nutrients, chlorophyll a, and the biological planktonic components. Studies on the heatwave effects on Mediterranean planktonic communities considering the entire planktonic trophic web are very limited, especially in freshwater environments. Projections suggest rising temperatures will lead to a decline in plankton biodiversity, favouring smaller species and causing energy, nutrient, and carbon losses across the food web. In addition, the affirmation of potentially harmful microalgae and pathogenic bacteria is expected to increase under warming. This is especially important to be detected in vulnerable environments such as Mediterranean artificial lakes, mainly used for producing potable water.