Italian Volcanic lakes: a diversity hotspot and refuge for European charophytes

Macrophytes are one of the most important components of primary producers in lacustrine environments. Charophytes represent the most threatened group of macrophytes and are included in many European Red-Lists. Thus, finding and preserving charophyte diversity hotspots is important for European macrophyte conservation strategies. Within the framework of a general project aimed at investigating aquatic plant diversity of Italian volcanic lakes (IVL), a field survey carried out in 2009-2010 recognized high charophyte diversity. Overall, 17 species of charophytes, which correspond to 50% of Italian stoneworts and 30% of the European species, were recorded. Nevertheless, only four IVL out of the nine lakes investigated can be considered Chara-dominated lakes. Three Chara-vegetation belts characterized the Chara dominated IVL, as in other pristine deep calcareous European lakes. A Chara aspera belt grew at a lower depth, followed by a Chara polyacantha belt at a medium depth and a Chara globularis dominated belt at a higher depth, up to the maximum growing depth. The most common species was Chara globularis, whereas seven species were rare. Sixteen of the 17 species found belong to the IUCN threatened categories throughout Europe. The most interesting taxa are Nitella hyalina, Nitella gracilis and Lychnothamnus barbatus. Nitella hyalina is extinct in Switzerland and Great Britain, critically endangered in the Balkans and in Germany. Nitella gracilis is extinct in Denmark and endangered in the Balkans, Sweden and Switzerland. The Lychnothamnus barbatus population found in Martignano is the only one known in Italy. Lakes Vico, Martignano, Bolsena and Bracciano host from 18% to 44% of European charophytes. The high number of species in each lake allows the selection of these lakes as European hotspots of charophyte diversity. Therefore, the IVL can be a reference system for the conservation of aquatic species that are typical of Italian and European deep lakes.