Petola

Cultivation of petola

The spatial and technological development of salt marshes on the Slovenian coast has been marked by a number of important turning points. In the 14th century, the crystallisation beds of the salt fields began to be used for the cultivation of “petola”, an artificially cultivated crust composed of cyanobacteria (Microcoleus chthonoplastes and other species), gypsum, carbonate minerals and, to a lesser extent, clay.

The role of the heel is twofold: firstly, it prevents the salt from mixing with the marine mud at the bottom of the crystallisation bed, but it also acts as a biological filter, as it prevents the incorporation of individual ions, e.g. iron and manganese ions, into the halite. After the preparation of the base of the crystallisation beds, algae and cyanobacteria colonise the surface of the sludge within a few weeks.

The salt pans of Tejo and Sado in Portugal had a similar method of extracting salt. There it was also known as casco, an artificially grown carpet. Production on this basis has recently been abandoned.

A petola is a cross-section of a few mm thick, firmly adherent gelatinous carpet of cyanobacteria. It is black in colour and is impregnated with gypsum, carbonate minerals and clay. Algal growth on the sediment stabilises its surface.

The surface of the petola provides an environment suitable for the growth of photoautotrophs (cyanophytes, algae - chlorophytes and diatoms), which form an oxygen-rich layer. The amount of oxygen produced by a petal on the same surface area is equivalent to the amount of oxygen produced by a tropical rainforest of 30 to 40 m in height. The upper layer is brown and dominated by cyanophytes such as Enthopysalis and Lyngbya. The lower layer is dominated by Microcoleus chthonoplastes, one of the hardiest species of cyanobacteria, able to withstand up to ten times the concentration of seawater.

The surface of the petola provides an environment suitable for the growth of photoautotrophs (cyanophytes, algae - chlorophytes and diatoms), which form an oxygen-rich layer. The amount of oxygen produced by a petal on the same surface area is equivalent to the amount of oxygen produced by a tropical rainforest of 30 to 40 m in height. The upper layer is brown and dominated by cyanophytes such as Enthopysalis and Lyngbya. The lower layer is dominated by Microcoleus chthonoplastes, one of the hardiest species of cyanobacteria, able to withstand up to ten times the concentration of seawater.