Silent survivors: diatom resilience in Mediterranean Temporary Ponds

Mediterranean Temporary Ponds (MTPs) are ephemeral freshwater habitats hosting a large number of aquatic and terrestrial organisms. Among these, diatoms represent the bioindicators that contribute mostly to Earth's global primary production. Herein, we focused our attention on the role of seasonality and hydroperiod on benthic diatoms of MTPs. We analyzed the diatom community turnover along one year in two MTPs in the Latium region, Italy. The two MTPs showed different levels of anthropogenic pressures. Our results demonstrated that hydroperiod length and seasonality showed a moderate influence on diatom richness of MTPs; in particular, although the highest number of species was found during spring, taxonomic diversity remained stable at seasonal and inter-annual level despite strong changes in community composition and hydroperiod length. Overall, sampling sites showed different ecological conditions and chemical drivers: protected site was dominated by species occurring in minimally impacted oligo- to mesotrophic waters; unprotected site with high EC and ORP was dominated by species occurring in euryhaline brackish waters. Moreover, physicochemical parameters showed a low influence on diatom assemblages in the protected site and a strong influence in the unprotected site. No significant correlation between diatom ecological guilds and physicochemical parameters emerged. While for all the seasons the dominant guild was the motile guild, no inter-season variations emerged: diatom communities and ecological guilds in MTPs are resilient to seasonal variations. To provide novel insights, future research should focus on additional environmental drivers such as nutrient availability, sediment composition, and hydrological variability, including long-term monitoring plans.