Abstract:

Rich, diverse assemblages comprising a total (live + dead) of twenty-one ostracod species belonging to fifteen genera were recovered from phreatic waters of the hypogenic Frasassi Cave system and the adjacent Frasassi sulfidic spring and Sentino River in the Marche region of the northeastern Apennines of Italy. Specimens were recovered from ten sites, eight of which were in the phreatic waters of the cave system and sampled at different times of the year over a period of five years. Approximately 6900 specimens were recovered, the vast majority of which were disarticulated valves; live ostracods were also collected. The most abundant species in the sulfidic spring and Sentino River were Prionocypris zenkeri, Herpetocypris chevreuxi, and Cypridopsis vidua, while the phreatic waters of the cave system were dominated by two putatively new stygobitic species of Mixtacandona and Pseudolimnocythere and a species that was also abundant in the sulfidic spring, Fabaeformiscandona ex gr. F. fabaeformis.
Pseudocandona ex gr. P. eremita, likely another new stygobitic species, is recorded for
the first time in Italy. The relatively high diversity of the ostracod assemblages at Frasassi
could be attributed to the heterogeneity of groundwater and associated habitats or to
niche partitioning promoted by the creation of a chemoautotrophic ecosystem based on
sulfur-oxidizing bacteria. Other possible factors are the geologic age and hydrologic
conditions of the cave and karst aquifer system that possibly originated in the early–
middle Pleistocene when topographic uplift and incision enabled deep sulfidic waters to
reach the local carbonate aquifer. Flooding or active migration would have introduced
the invertebrates that now inhabit the Frasassi Cave system