Jellyfish Population Rises in Marmara Sea

A research project titled "Causes and Consequences of Jellyfish Population Increases in the Sea of Marmara," initiated by Istanbul University's Faculty of Aquatic Sciences and the Ministry of Environment, Urbanism and Climate Change, was conducted in the Sea of Marmara using the R/V Yunus-S vessel. Underwater observations were carried out in the Sea of Marmara by divers, and samples were collected. Additionally, jellyfish samples were collected from different depths and examined. Prof. Dr. Melek İşinibilir Okyar, Dean of the University's Faculty of Aquatic Sciences, stated that serious jellyfish population increases have been experienced in recent years in Turkey's seas, as well as worldwide. Okyar noted that jellyfish have the ability to utilize their negative ecosystem changes to their advantage and are successful at survival, stating, "These are creatures that have sustained their existence on Earth for 500 million years, increasing their numbers and diversity." Prof. Dr. Okyar expressed that the Sea of Marmara is under intense human pressure from various causes, which creates favorable conditions for jellyfish population increases. Drawing attention to the fact that jellyfish are organisms that tolerate polluted areas, Okyar said, "Their reproductive capacity increases with temperature rise. Due to global warming, these temperature increases exist in all seas. In the Sea of Marmara, despite it being winter, the water temperature was measured at approximately 20 degrees Celsius. This temperature increase triggers jellyfish reproductive activities. In recent years, we are seeing intense jellyfish population increases across the entire Sea of Marmara, but particularly in the coastal areas of the Sea of Marmara and in gulfs, especially along Istanbul's coastline."

"We conducted the first phase of the project in Eastern Marmara"

Prof. Dr. Okyar stated that work was initiated by the Ministry of Environment, Urbanism and Climate Change and the Faculty of Aquatic Sciences to determine the causes of jellyfish population increases. Emphasizing that they implemented the first phase of the project in Eastern Marmara, Okyar noted, "When jellyfish overpopulate, they die after a certain period and begin to decompose. This causes deterioration of water quality and changes in ecosystem functioning."

Prof. Dr. Okyar continued his remarks, emphasizing that in studies using drones they detected jellyfish spreading over large surface areas:

"In addition, we conducted dives to identify specifically which water masses they accumulate in. We determined that jellyfish are more abundant particularly between 5 and 10 meters depth. While jellyfish appear sporadically on the water surface, they actually maintain massive stocks at 5 meters depth. In the second phase of the project, we will conduct scuba diving to track their life stages and follow the seasonal process of their reproduction in the ecosystem. Due to climate change, many new invasive jellyfish species are entering the Sea of Marmara. In our recent studies, we found many new species. These have begun increasing their abundance. With the entry of new species, the load of dissolved organic matter dependent on jellyfish in the marine ecosystem is increasing." Referring to the fact that organisms feeding on jellyfish are declining due to various pressures in the ecosystem, which removes predatory pressure on jellyfish and causes their numbers to increase, Okyar said, "Jellyfish population increases are now occurring in every season. Triggered by global warming, jellyfish have shown excessive increases over the last 20-30 years." Prof. Dr. Okyar noted that jellyfish transported by the Sea of Marmara's current system accumulate particularly in the eastern basin of the Gulf of Izmit, creating serious problems for this region. Mentioning that these organisms, which are harmful to the marine ecosystem, are consumed as food in the Far East, Okyar added that they are working to obtain products from jellyfish that would provide economic benefits. Source