There are still blank areas on the map of distribution of silica-scaled chrysophytes in Europe, the subtropical regions are especially understudied. Here, a survey of species from nine sampling sites from the Istrian Peninsula is provided.
In total, only 17 mostly cosmopolitan or widely distributed species were recorded. A relatively low number of species per locality (3.7 on average) might be a consequence of low connectivity of freshwater bodies in the Istrian Peninsula, and higher levels of conductivity and pH, caused by carbonate and flysch bedrock.
Species known to prefer or tolerate higher levels of those factors were especially prevalent in the investigated sites (e.g. Mallomonas heterospina and M. alata).
Resistant silica scales make silica-scaled chrysophytes a flagship group of organisms to study the biogeography of protists. Records of species from European humid subtropical climate regions have not been published to date, and the current paper may help to fill in the missing information.