The Size Structure of the Zooplankton Community Reflects Better the Trophic Status of Mediterranean Ponds Than the Taxonomic Structure

Abstract

1. Ponds are key habitats for regional freshwater biodiversity and play a fundamental role in enhancing connectivity between aquatic ecosystems. Despite their importance, ponds are one of the most neglected water ecosystems due to their small size and are particularly affected by climate change and anthropogenic activities. Zooplankton communities serve as sensitive indicators of environmental stressors, such as changes in trophic state, hydroperiod variability, and habitat degradation. Therefore, understanding the drivers of biodiversity and the size structure of the zooplankton community in Mediterranean ponds is important, as it provides valuable insights into how different stressors may impact this community and ecosystems, and provides valuable insights for making appropriate decisions for its conservation. 2. Here, we evaluated the taxonomic and size structure of the zooplankton community and its relationship with trophic status, the presence of fish, macrophyte abundance, morphometry, hydroperiod variability, and land use by conducting a comprehensive ecological characterisation of 30 Mediterranean freshwater ponds. 3. Our results suggest that size metrics are affected by factors related to the trophic status of ponds. Eutrophic ponds, with the highest chlorophyll-a concentration, oxygen supersaturation, presence of fish, and low habitat complexity (i.e., fewer macrophytes), were dominated by small-size zooplankton, and the community was less size diverse (i.e., steeper slope of the size spectra and lower size diversity values). Also, ponds with a high habitat complexity and lower surface area had higher zooplankton biomass (i.e., higher intercept of the size spectra). In contrast, zooplankton richness was only positively influenced by pond surface area. 4. Our results showed that size metrics reflected changes in the zooplankton community along the trophic status and biotic gradients, whereas the taxonomic metrics were more related to the morphometry of ponds. 5. Size-related variables can be effective tools to evaluate the drivers of change of pond communities in the Mediterranean region and possibly others, particularly when taxonomic metrics do not show a significant response. From a management perspective, the results demonstrate the potential of size-based metrics for assessing the ecological status of Mediterranean ponds.