The closure of the North Crimean Canal led to an increase in the salinity of the Sivash Bay, as a result of which the species diversity of benthic microalgae decreased. At the same time, the total productivity of those species that can exist in new more severe conditions even increased, which indicates a high bioresource potential of the reservoir. This conclusion was made by Russian scientists after studying the state of the ecosystem of the Sivash Bay.
The results of the work, supported by a grant from the Russian Science Foundation (RSF), are published in the journal Water. Sivash Bay, the largest lagoon in Europe, is located on the eastern coast of the Crimean Peninsula and is connected to the Sea of Azov by a narrow strait. As a result of human activity, the salinity in it changed dramatically twice.
Initially, the Sivash was a hypersaline reservoir: the salt concentration reached 140 ppm, which is seven times higher than the values for the Black Sea. To supply the Crimea with fresh water in the 1970s, the North Crimean Canal was built, through which the Dnieper water began to flow to the peninsula. Irrigated agriculture began to develop, drainage water from the fields began to be discharged into the lagoon, and the salinity in it decreased to 20-25 ppm.
In 2014, Ukraine cut off the supply of fresh water to the canal, and Sivash again became hypersaline. At present, the salinity in the bay varies from 100 ppm in the south to just over 30 ppm in the north, where it is connected to the Sea of Azov.
Scientists from the A. O. Kovalevsky Institute of Biology of the Southern Seas of the Russian Academy of Sciences (Sevastopol) investigated how the increase in the salinity of the Sivash Bay after the closure of the North Crimean Canal influenced the diversity and abundance of microalgae in the water area. Microscopic algae and cyanobacteria (the so-called microphytobenthos) that live on the bottom and on other larger macroalgae play a huge role in the life of all aquatic ecosystems.
They enrich the water with oxygen, and also serve as food for various aquatic animals. Therefore, changes in the diversity and abundance of microalgae in the bay significantly affect the food chains and habitats of other species.
Biologists analyzed the species composition and abundance of microphytobenthos in water samples from different parts of the Sivash Bay and found 40 species of microalgae and cyanobacteria. Comparison with earlier studies conducted before the closure of the North Crimean Canal showed that the diversity of microscopic vegetation in the lagoon decreased by 36 percent after salinity increased.
In addition, most (69 percent) of the algal species previously inhabited in the Sivash are no longer found there, and they have been replaced by others, more adapted to hypersaline conditions. Changes in the species composition of microphytobenthos caused rearrangements in the entire ecosystem of the bay.
For example, fish practically disappeared in the lagoon, but other valuable species of animals used as food began to develop intensively - gill-legged crustaceans of brine shrimp and larvae of bell mosquitoes (bloodworms), in the productivity of which microalgae play a significant role.
Another interesting observation was that in parts of the bay with very high salinity, microalgae grow in abundance. This can be explained by the fact that few animals can live in hypersaline waters, and therefore there is no one to control the amount of algae. However, it is unlikely that only salinity contributes to the rapid growth of microphytobenthos, since the values of many other important factors have changed in the bay: temperature, oxygen content in the water, and the amount of organic matter.
“The results of our work clearly indicate that a sharp increase in water salinity in the Sivash Bay after the closure of the North Crimean Canal led to a change in the ecosystem of the lagoon and a difficult socio-economic situation in the region: due to an increase in salinity in the bay, fishing became impossible, the possibilities of irrigated agriculture. However, focusing on negative consequences is counterproductive.
The transition of Sivash and its surrounding ecosystems to new alternative states closes the existing opportunities for nature management, but opens up new ones, you just need to see them. Huge populations of brine shrimp and bloodworms have formed in the bay, their intelligent exploitation can give even more income than fishing provided,”says Elena Anufrieva, project manager for a grant from the Russian Science Foundation, Ph. D.