Coping with the “Racovitzan impediment” in caves: unexpected discoveries open new horizons to the knowledge of groundwater copepods in southern Italy

The stygobitic copepods of southern Italy are known in spots, and species’ records are limited to a few caves and some wells sampled in the past decades. Nevertheless, the groundwater biodiversity of the Apulia region is probably the most well-known in the Italian peninsula. From a biogeographic perspective, the Apulia region constitutes the Apulian Stygoprovince, and its groundwater fauna differs from those of the Apennines and Alpine area. The Apulia Region is the main karstic area of southern Italy. The complex geodynamic history of the area accounts for its litho-stratigraphic succession, the overall geomorphology, and karst evolution. More than 2000 natural caves are present, many of which are along the seashore. This composite paleogeographic scenario may have determined differences in groundwater assemblages, mainly, in terms of species composition. The present study aims at analysing the copepod assemblages of three caves belonging to distinct Apulian hydrogeological districts and characterised by different salinity ranges. Rotolo Cave is a freshgroundwater cave located about 12 km from the Adriatic coastline; Grotta Puntore is a brackish system opening about 500 m far from the Adriatic Sea, and Zinzulusa Cave is an anchialine cave located in the southernmost part of the Salento peninsula. Our investigations confirmed the presence of 7 out of the 17 stygobitic species already known for the Apulian region extending the distribution patterns of the harpacticoids Nitocrella stammeri, Stammericaris orcina, Elaphoidella elaphoides, Troglophonte spelaea, and of the cyclopoids Halicyclops dalmatinus, Metacyclops stammeri and Diacyclops lindae. Remarkably, three new stygobitic species were discovered: a new species of the rare ectinosomatid harpacticoid Pseudectinosoma and a new species of the ameirid harpacticoid Nitokra from Grotta Puntore. Surprisingly, a new species of the cyclopoid genus Hesperocyclops was collected from a single subhabitat in the unsaturated karst of Grotta Rotolo, thus expanding the distribution of this genus in the Palaearctic region. Zinzulusa Cave hosts the highest copepod species richness, 80% composed of stygobites mostly of direct marine origin, followed by Grotta Puntore, where thalassoid species overrule limnicoid ones. The endemicity score of Grotta Puntore was the highest among the three caves in the present study. Grotta Rotolo showed the lowest stygobitic species richness and endemicity score. The three caves showed sharp differences in stygobitic species assemblages, likely reflecting the different paleogeographic events of the three karst areas and, consequently, the different colonisation pathways followed by the epigean ancestral populations to enter groundwaters.