ECO-PHYSIOLOGICAL, TAXONOMICAL AND PALEOLIMNOLOGICAL STUDY OF DINOFLAGELLATES OF LAKE NERO DI CORNISELLO (ADAMELLO BRENTA NATURAL PARK, TRENTINO, ITALY)

The Subphylum Dinoflagellata belongs to the Phylum Alveolata. Dinoflagellates are among the most important primary producers in aquatic environments. The low alkalinity high mountain Lake Nero di Cornisello (2233 m a.s.l., Adamello-Brenta Natural Park, Trentino, NE Italy) has been selected as case-study, in the frame of this Ph.D. thesis, to evaluate the potential of dinoflagellates in paleolimnology as biological proxies. Studies on the taxonomy, eco-physiology of living dinoflagellates and quali-quantitative analyses of their organic-walled cysts in sediments were performed. A multidisciplinary approach has been applied, with seasonal monitoring of the physical-chemical characteristics of the lake, in situ study of the seasonal dynamics of phytoplankton, in vitro study of the eco-physiology, morphology and taxonomy of the dominant dinoflagellate species and a quali-quantitative sediment core study of the preserved organic-walled dinocysts. Two dinoflagellate species, Peridinium umbonatum var. umbonatum (P.u.) and Peridinium cinctum (P.c.) are the main primary producers of Lake Nero di Cornisello during spring and summer. The dominance of P.u. over P.c. during the period of proliferation could be caused by the precocity in encystment and excystment. The cyst of P.u. in possession of an original hypocystal archeopyle. P.u. has maximum germination percentage at pH 6 and at 4°C, but it also excysts at pH from 4 to around 9. This species doesn’t need prolonged exposure to light to germinate and grow. P.u. is a species obligated to oligotrophic conditions needing low amounts of nutrients for germination and growth. Three peridinioid organic-walled cyst morphotypes have been found in Holocene sediments of Lake Nero di Cornisello. A detailed observation of the dinocysts and comparison with P.u. cysts suggests that the peridinioid dinocyst morphotype 1 belongs to the dominant species living at present in the lake. Detailed observations on morphotype 2 show that also this dinocyst belongs to the species P. umbonatum, but it differs from morphotype 1 in size and general morphology. Morphotype 2 is usually bigger. The third morphotype, more rounded, probably belongs to the genus Peridinium as well. The analyses of the trends of the three dinocyst morphotypes in the sediment core and their comparison with other proxies permitt to postulate an historical description of environmental and climate changes occurred in Lake Nero di Cornisello. On the basis of my experience it is possible to postulate that the study and use of dinoflatellates as biological proxies in paleolimnology is possible, potentially providing important information on climate and environmental changes.