Glenodinium sanguineum March. and the reddening phenomenon of Lake Tovel: biological and environmental aspects

Glenodinium sanguineum March. is known to be responsible of reddening in alpine Lake Tovel (Trento, Italy) in Brenta's Dolomites. The dinoflagellate has no longer significantly bloomed since 1964 AD, failing to give red color to the lake's water. Nowadays this is an oligotrophic lake, but very few physical and chemical data are available for the period pre-1964 because many studies focussed on the taxonomic position of the algae and on the reddening mechanisms. Several hypothesis have been formulated over the years to explain the ending of the blooms, among which lower surface water temperatures due to modifications in the hydraulic regime and changes in nutrient status are the most accredited. Recently, short-term enclosure experiments demonstrated that phosphorus is a key factor in regulating the G. sanguineum blooming. In this review, we outline all the hypotheses formulated but not yet demonstrated over the years, in an effort to better understand the cause of the lack of the algal reddening phenomenon on Lake Tovel. Finally, new avenues for future studies are suggested with special reference to the elucidation of possible impact of environmental conditions on Glenodinium cycle and carotenogenesis.