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How it all began: diatoms

 

The periphyton, algae growing on tufts of moss and on rocky surfaces, consists of diatomaceous algae, also called diatoms

The presence of algae and mosses is an important requirement for the creation of travertine, especially in determining the form it will take. The periphyton, algae growing on tufts of moss and on rocky surfaces, consists of diatomaceous algae, also called diatoms. A total of 276 taxa of diatoms, belonging to 69 families, have been recorded at studied sites in the Krka River. Due to their sensitivity and rapid response to the physicochemical and biological changes in the river, they are excellent biological indicators. The types of microhabitats found in the Krka River are in fact a hotspot of diversity for freshwater algae.

Diatoms are single-celled, autotrophic organisms characterised by their cell walls that contain silica. Diatoms make up to 70% of the total autotrophic components in periphyton communities, and play an important role in carbon fixation. They can be found in virtually every aquatic environment, and they are the dominant form of plant life in ice ecosystems. With 12,000 described species, this is the largest group of algae, though it has been assumed that there may be up to 100,000 different species. Diatoms create deposits called diatomaceous earth. These species are often used in monitoring water quality and monitoring toxic and invasive species, in climate change studies, and in studies on speciation and evolution. Diatoms are algae that have a transparent cell wall made of silicon dioxide. Silica is the main component of glass, and the hydrated form creates opaline glass, so diatoms are often described as living in a glass or opaline house.

The most common diatom genera in the Krka River are the NaviculaGomphonema and Cymbella. At the Krka source, 25 diatom taxa have been found, 52 species in the upper course, 105 species in the lake-like expansion under the Krka monastery, 150 at Roški slap, 126 in Visovac Lake, 93 along the transect from Lozovac to Visovac Lake, and 147 at Skradinski buk. The highest diversity of species (81) and genera (40) was found at the marshy lake-like expansion near Roški slap and in the Marasovića Lake near Skradinski buk.

The project Diatoms of the Krka River – from the source to the mouth aims to compile a systematic list of the diatoms present in the Krka River, and create permanent slides of these species. This in turn led to the idea of establishing the Croatian National Diatom Collection. This is a collection of permanent slides of diatom samples collected in Croatia, and is the first institutional collection of diatomaceous algae in Croatia. The collection currently includes more than 6000 slides, which are in the process of being categorised, with ongoing collections of new slides. Among them are the type materials for species new to science, that are being described by the scientists at the Faculty of Science, University of Zagreb, and now they are no longer being sent to other European collections, but remaining in Croatia, as a national treasure of our species diversity. Collections such as these are a priceless treasure, as in addition to providing information about biological research, they provide insight into the diversity of diatom species, the biodiversity of a certain area, the distribution of diversity, and changes in time and space. This makes it possible to implement effective project of the priceless treasures of Croatia’s biodiversity.