Temporary Ponds as Overlooked Refugia for Red List Diatom Species: Implications for Conservation

The proposed study addresses diatom Red List knowledge gap by offering new insights into the occurrence, elevational distribution and seasonal preferences of Red-Listed diatom species inhabiting temporary ponds. The study was conducted in central Italy, where a total of six temporary ponds, located along an elevational gradient (0, 400, 800, 1200, 1600 and 2000 m a.s.l.) were sampled for 1 year, one sample per month. Overall, 27 out of 234 species are classified within one or more threat categories (11.5%). Fifty-nine species were classified as Not Evaluated (NE) and 8 as Data Deficient (DD), while the majority of species (140) were assigned to the Least Concern (LC) category, indicating a predominance of widespread taxa. A smaller number of species were classified as Rare (RA; 7 species) and Near Threatened (NT; 10 species), while Vulnerable (VU) and Endangered (EN) categories accounted for 7 and 3 species, respectively. Most of the rare and threatened diatom species (RA, NT, VU and EN) were recorded in the lower to mid-elevation ponds, particularly between 0 and 1200 m. In contrast, ponds at mid elevations (TP800 and TP1200) supported the greatest diversity of LC and DD species. Summer season exhibited the highest overall richness across Red List categories, with particularly elevated numbers of LC (98 species) and NE taxa (36). This season also supported the greatest representation of threatened categories, including the highest values for NT (7 species), VU (4) and EN (3) taxa. From an ecological perspective, our results highlight that both Mediterranean and alpine ponds host, in the regional context investigated, conservation-relevant diatom assemblages, albeit expressed within narrow temporal windows, with important implications for the conservation and management of temporary ponds.