Zooplankton size structure reflects the trophic status of ponds along a latitudinal gradient

Abstract

Despite increasing research on warming and biodiversity, knowledge on how temperature shapes community size structure remains limited, which is one of the main challenges in assessing the consequences of climate change. This gap is evident in vulnerable ecosystems like ponds, crucial for aquatic biodiversity but highly sensitive to temperature increases due to their small size. This study assessed the main climatic and local drivers influencing zooplankton community size structure in 141 ponds across four European countries and Uruguay, covering a wide latitudinal and trophic gradient with standardized sampling. Using linear mixed models, results revealed that local factors, such as trophic status and morphometric pond characteristics, were more consistently associated with size-spectrum parameters than climatic variables. The normalized size spectrum slopes (ordinary least square regression, OLS) became steeper with higher chlorophyll a (Chl a) concentrations, reflecting dominance of small zooplankton, suggesting reduced energy transfer efficiency to higher trophic levels, and possibly weaker top-down phytoplankton control. Conversely, ponds with lower Chl a showed flatter slopes, indicating more large zooplankton and possibly greater top-down control. The overall intercept was higher in deeper ponds with abundant aquatic vegetation, suggesting greater overall abundance across size classes. Size spectrum metrics did not vary significantly along climatic gradients. These results suggest that zooplankton community size structure in ponds appears to be more closely related to local environmental conditions than large-scale climatic gradients. This highlights the key role of local habitat characteristics in shaping zooplankton size structure and energy transfer dynamics.