Meduse e bivalvi d’acqua dolce

Olindiid freshwater jellyfishes of the genus Craspedacusta Lankester, 1880 are native to eastern Asia; however, some species within the genus have been introduced worldwide and are nowadays present in all continents except Antarctica. To date, there is no consensus regarding the taxonomy within the genus Craspedacusta due to the morphological plasticity of the medusa stages. The species Craspedacusta sowerbii Lankester, 1880 was first recorded in Italy in 1946, and until 2017, sightings of the jellyfish Craspedacusta were reported for 40 water bodies. Here, we shed new light on the presence of the freshwater jellyfishes belonging to the genus Craspedacusta across the Italian peninsula, Sardinia, and Sicily. First, we report 21 new observations of this non-native taxon, of which eighteen refer to medusae sightings, two to environmental DNA sequencing, and one to the finding of polyps. Then, we investigate the molecular diversity of collected Craspedacusta specimens, using a Bayesian analysis of sequences of the mitochondrial gene encoding for Cytochrome c Oxidase Subunit I (mtDNA COI). Our molecular analysis shows the presence of two distinctive genetic lineages: (i) a group that comprises sequences obtained from populations ranging from central to northern Italy; (ii) a group that comprises three populations from northern Italy—i.e., those from the Lake Levico, the Lake Santo of Monte Terlago, and the Lake Endine—and the single known Sicilian population. We also report for the first time a mtDNA COI sequence obtained from a Craspedacusta medusa collected in Spain.

In September 2019, thousands of colonies of the freshwater bryozoan Cristatella mucedo Cuvier, 1798 (Phylactolaemata: Cristatellidae) were discovered during dives in the Large and Small Lake of Monticolo / Montiggl (Province of Bolzano / Bozen, Italy) between 3 and 5 m of depth. They were attached on large stones and submerged branches. The colonies ranged from about 1 cm to over 10 cm in length. Within the framework of a study carried out in the years 2019 – 2020 in the two lakes aiming at documenting the colonies, also free statoblasts (spinoblasts), resistant dormant stages with diameters between 700 and 750 μm, were found. This is the first confirmed record of C. mucedo in South Tyrol.

Nel settembre 2019 nel Lago Grande e nel Lago Piccolo di Monticolo (Provincia di Bolzano) durante immersioni subacquee sono state avvistate per la prima volta migliaia di colonie del briozoo d’acqua dolce Cristatella mucedo Cuvier, 1798 (Phylactolaemata: Cristatellidae), su grandi pietre e rami sommersi tra i 3 e i 5 m di profondità. Le colonie erano lunghe da circa 1 cm a oltre 10 cm. Nei due laghi di Monticolo colonie di C. mucedo sono state trovate negli anni 2019 – 2020 da giugno a ottobre e nel mese di ottobre sono stati raccolti statoblasti, stadi dormienti resistenti, con diametro tra 700 e 750 μm. Si tratta della prima segnalazione di C. mucedo in Alto Adige.

The freshwater bivalves Unionidae are in dramatic decline globally. Due to wide shell variability, only the genus can be determined by traditional morphological methods, with genetic analyses being required for species identification. From November 2018 to October 2020 four freshwater bodies in the Province of Bolzano/Bozen (Italy) (Small Lake and Large Lake of Monticolo/Montiggl, Lake Caldaro/ Kaltern, and its main emissary Fossa Grande di Caldaro/Großer Kalterer Graben) have been explored to collect unionid bivalves by hand and scuba diving. Unionid presence, bathymetric distribution, biometric characteristics, and attachment of invasive allochthonous zebra mussel (Dreissena polymorpha) were detected.
Molecular barcoding analyses (COI) on foot snips from 25 specimens (19 Anodonta and 6 Unio) confirmed the presence of four native species: Anodonta anatina, A. cygnea, A. exulcerata, and Unio elongatulus. Most Anodonta specimens from both Small (78 %) and Large Lake of Monticolo (60 %) were parasitized by Dreissena polymorpha in numbers ranging from 1 to 81 per individual. The biomass of D. polymorpha amounted up to 41 % of Anodonta’s weight. D. polymorpha was not found in Lake Caldaro/Kaltern and its emissary Fossa Grande di Caldaro/Großer Kalterer Graben.

The freshwater jellyfish Craspedacusta sowerbii Lankester 1880 is a cryptic cosmopolitan invasive species, which occurs in all continents except Antarctica. Recent molecular studies suggest the existence of at least three very different genetic lineages of Craspedacusta: the “sowerbii”, the “kiatingi”, and the “sinensis” lineages. We report the presence of both medusae and polyps of this alien taxon in the Large Lake of Monticolo / Montiggl, a meso-eutrophic natural lake in the Province of Bolzano / Bozen in Northern Italy. Molecular analyses of mitochondrial 16S sequences showed that this population belongs to a different lineage than that recently described for Sicily (Southern Italy). Therefore, there are two different genetic lineages of C. sowerbii in Italy. In the Large Lake of Monticolo / Montiggl medusae were observed in 6 consecutive summers (2015–2020), from July to September. All the examined medusae were males. The stomach content analyses showed that zooplanktonic copepods and cladocerans with size range between 0.3 and 0.8 mm were the preferred prey of medusae. Polyps of C. sowerbii were recorded in the lake on the zebra mussel Dreissena polymorpha in shallow water and on the underside of artificial substrates. The analyses of zebra mussels would therefore be a simple method to check for the presence of the polyp stage of C. sowerbii in various aquatic environments.