The Role of Climate Warming and Thermal Stratification in the Ecological Success of Diaphanosoma brachyurum in Lake Maggiore

Deep temperate lakes are increasingly reported to suffer consequences of climate warming, affecting thermal stratification and plankton seasonality. Long-term studies offer a unique opportunity for detecting changes in the zooplankton taxa composition related to climate change. Sampling zooplankton organisms alongside abiotic variables, such as water column temperature, enables the linking of changes in plankton communities with variations in the stratification regime. This provides evidence of direct and indirect warming effects. Our study in Lake Maggiore investigated variations in the population density and persistence of Diaphanosoma brachyurum, a thermophile species that is a member of the original zooplankton community of the lake, along with the increase in water temperature and the duration of the thermal stratification during the period 2013–2023. Our results highlighted an increase in the abundance and persistence of Diaphanosoma during the study period, along with an increase in the mean water temperature of the layer 0–10 m and of the length of the thermal stratification. Such changes, affecting the population dynamics of predators and competitors and their food sources (i.e., small algae), might lead to a rearrangement of the structure of the pelagic food chain.