Ecology of biotic communities of thermal springs: early studies on Cyanobacteria in Sardinia (Italy)

The ecology of thermal springs is still poorly studied compared to other types of freshwater ecosystems, despite their importance as hot-spots of biological diversity and their socio-economic value. The thermal springs communities are composed of a relatively small number of species with a cosmopolitical geographic distribution, genetically differentiated and isolated on the local scale. Eight thermal springs (Casteldoria, Caddas 1, Caddas 2, Oddini, San Saturnino, Abbarghente, S. Giovanni Su Anzu, San Martino), belonging to five hydrographic basins, were investigated, with the main aim of studying, for the first time in Sardinia, some aspects of the ecology of their living communities, considering in particular the Cyanobacteria, one of the main groups of microorganisms inhabiting these ecosystems. Water samples for chemical, physical and nutrients determination and Cyanobacteria were sampled in summer 2016 and winter 2017. Cyanobacteria were collected from different substrates: rock and pebbles (epilithic), macrophytes (epiphytic) and fine sediment (epipelic). The number of taxa varied from 8 (S. Giovanni su Anzu) to 15 (San Saturnino). The percent species composition revealed that the most important species were Leptolyngbya thermalis, Leptolyngbya laminosa and Oscillatoria sp. in San Saturnino; Oscillatoria sp., L. thermalis and Planktothrix sp. in Abbarghente; L. laminosa, L. thermalis and Lyngbya sp. in Fordongianus (Caddas 1 and 2); L. thermalis, Oscillatoria spp. and Lyngbya spp. in Casteldoria, San Martino and Oddini; L. termalis, Oscillatoria sp. and Synechococcus sp. in S. Giovanni su Anzu. The presence of species potentially toxic, such as Mastigocladus laminosus, Lyngbya nigra and Cyanosarcina sp., were found in Abbarghente, Caddas 1, S. Giovanni Su Anzu, San Martino and San Saturnino. Our preliminary results indicate an unexpected biodiversity of the investigated thermal springs and highlight the importance of further in deep studies to construct a robust ecological knowledge of these peculiar ecosystems for supporting their management and protection.