Rising Salinity in Don River Unlikely to Bring Jellyfish to Rostov
The increase in salt concentration in the water of the Don River delta is unlikely to reach levels that would allow jellyfish from the Sea of Azov to enter the river, according to experts.
Jellyfish reproduction in the Sea of Azov directly depends on water salinity. At average levels below 10 parts per thousand, their development practically stops. When salinity rises to 13 ppt, intensive population growth is observed.
“The scenario of water salinity increasing to 10 ppt in the Don River up to the first major water intakes is unlikely,” note experts at the Azov Scientific Research Institute of Fisheries (AzNIIRKH).
The reduction in the volume of fresh water coming from the Don has already led to the penetration of mineralized salt water into the water supply systems of Rostov-on-Don, Azov, and Taganrog. As explained by Klim Grigorenko, a researcher at the Southern Scientific Center of the Russian Academy of Sciences (RAS), scientists have repeatedly recorded cases where salty water flowed from taps in these cities.
The situation could worsen after the commissioning of the Bagayevsky hydro unit, as this will stop the discharge of fresh water from the Tsimlyansk Reservoir and potentially increase salinity in the delta.
The salinity of the Taganrog Bay and the Sea of Azov has already reached maximum values in the past 70 years. This has triggered a massive spread of jellyfish, which reduces the level of dissolved oxygen in the water and the intensity of phytoplankton blooms — the main food base for fish.
Autumn cooling compensates for this effect, as jellyfish begin to die off, releasing biogenic substances into the water. “Considering that the process of natural jellyfish die-off in the autumn period stretches over 2–3 months, no negative consequences for the Sea of Azov ecosystem have been noted from this,” reported AzNIIRKH.
In 2025, the cooling of the Sea of Azov occurred particularly slowly, so the die-off of jellyfish began only at the end of autumn.
