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  18.10.2019, 13:30h

The Diatoms of the Krka River

What are these puzzling single-cell organisms that live in virtually every aquatic environment on Earth and are responsible for half of the world's primary production?

These are the diatomaceous algae, also called diatoms. Their cells are covered with a layer of silicon dioxide, the main component in glass. When hydrated with a little water, it becomes the opalescent shell of the alga.

As part of the project The Diatoms of the Krka River – from the source to the mouth, conducted jointly by the Croatian Botanical Society; Department of Biology, Faculty of Science of the University of Science; Faculty of Science of the Sts. Ciril and Method University in Skopje, Macedonia; Ruđer Bošković Institute, and the Public Institute of Krka National Park, over the past two years research has been undertaken to gather the current knowledge and to systemise and revise lists and results of sampling from the source to the mouth of the Krka River. The main objective was to obtain a systematic list of diatoms in the Krka River, and to prepare permanent slides for archiving in the Croatian National Diatom Collection. The research results were presented at the Civitas Sacra Interpretation Centre of St. James' Cathedral in Šibenik on 18 October 2019.

“One of our long-term management objectives is to preserve the water quality of the Krka River and to protect the travertine formation process. These processes are unique and exceptionally sensitive, and therefore, this type of research is highly important, as it allows us to see that which cannot be seen by the human eye, and which is often times critical for maintaining biological balance and diversity. This project is one of the activities envisaged by the annual programme, which implements action plans listed in the ten-year Management Plan. These plans are a well-designed, carefully planned and responsibly implemented basis for managing protective areas,” said Nella Slavica, director of the Public Institute of Krka National Park.

At the research sites on the Krka River, a total of 276 diatom taxa were collected in different variations and forms, belonging to 69 genera. The most common species have a similar frequency of appearance in the research area, indicating that these species are characteristic for the Krka River. The most common frequencies in the Krka River are NaviculaGomphonema and Cymbella.

“The objectives of the Croatian Botanical Society, established in 2002, are the participation of its members in scientific and professional projects, designing and executing educational content, and promoting all botanical disciplines in the public. One of the important roles of the Society is promoting research based on field work and enlarging various collections. As a small country, though with a long tradition in algal research and world renowned scientists – algologists – the results of this project conducted in Krka National Park have given a significant contribution in obtaining knowledge, particularly in enlarging the National Diatom Collection of the Republic of Croatia,” stated Prof. Dr. Nenad Jasprica, president of the Croatian Botanical Society and project leader.

The presence of algae and mosses is an important requirement for travertine building, and in particular influences the shape of travertine. The vegetation of algae growing on moss and filamentous algae on rock surfaces comprise the diatomaceous algae. Due to their sensitivity and quick response to physico-chemical and biological changes in the water, they serve as excellent bioindicators. The microhabitats we find on the Krka make it a hotspot for freshwater algae diversity.

“The Conservation Service of the Public Institute of Krka National Park executes a wide range of projects aimed at protecting and conserving the park features, and implementing new knowledge and methodologies. The aquatic system is particularly sensitive and therefore, special attention is focused on it. We are exceptionally proud to be conducting this research in cooperation with the scientific community, to our mutual benefit. The park implements the results in its active protection measures, while the scientists publish the results in scientific articles. This project is the result of such cooperation. We are very proud of the diatom collection of the Krka River, which has initiated the formation of the national collection,” stated Gordana Goreta, head of the Department for the protection of water, travertine barriers and biological diversity.

Diatoms, or diatomaceous algae, are single-cell, autotrophic organisms characterised by a silicate shell called a frustula. They can make up to 70% of the total autotrophic components in overgrowth communities, and play an important role in carbon fixation. They can be found in virtually every aquatic environment, and they are the dominant life form in ice ecosystems. With 12,000 described species, this is the largest group of algae, though it has been supposed that the actual number of species could be up to 100,000. Diatoms create deposits that are called siliceous soil. They can be used to monitor water and monitor toxic and invasive species, in studying climate change, and studying speciation and evolution.

“The project Diatoms of the Krka River represents the initial idea and premise for the Croatian National Diatom Collection. This is a collection of permanent microscope slides of diatom species collected in Croatia, the first institutional collection of diatomaceous algae in Croatia. The collection is housed at the Department of Botany, Faculty of Science, University of Zagreb, and currently includes over 6000 slides. The collection is continuously being enlarged with new samples, and what is most important: type materials of new species to science, and so they are no longer going to other European countries, but instead are remaining in Croatia, as a national value of species diversity,” stated Dr. Marija Gligora Udovič, project leader.

As part of the project presentation, and exhibit was opened and can be viewed in the St. Nikola Tavelića Gallery at the entrance to the Civitas sacra Interpretation Centre until 26 October.