Turkish waters have been battling a critical mucilage issue for more than 20 years now. Though its occurrence changes from region to region and from time to time, the mucilage in the Marmara Sea has returned, becoming visible on the surface due to coastal accumulation in December 2024. Experts are alerting governments and citizens to act on this crucial issue, leading to irremediable damage to aquatic ecosystems and further human maritime activities.
To get to the root of the mucilage problem in the Marmara Sea and reflect on what should be done on both an individual and collective extent, the Head of the Department of Basic Sciences at the Faculty of Marine Sciences and Technology and the Dean of the Faculty of Applied Sciences at Çanakkale Onsekiz Mart University Prof. Dr. Yeşim Büyükateş gave an interview to The Istanbul Chronicle.
Mucilage, a sea snot or marine slime occurring when microscopic organisms found in marine systems proliferate under suitable environmental conditions, has become an alarming threat to marine life in Istanbul.
Formation of Mucilage
Büyükateş explained in our interview the scientific formation process behind mucilage, “It is generally formed by an increase in the number of phytoplanktonic organisms, particularly diatoms and dinoflagellates. Photosynthetic activity in phytoplanktonic organisms increases due to rising seawater temperatures, the increased angle of sunlight in spring, and longer daylight hours, leading to their rapid growth. When these organisms experience various forms of stress or when the levels of nutrients like nitrogen and phosphorus in the system fluctuate, they secrete various organic substances.” As a result of this combination, the mucilage, a gelatinous and sticky substance, forms.
Professor Büyükateş elaborated that the microscopic marine plants phytoplankton along with zooplankton, animal organisms that feed on them, bacteria that decompose organic matter, decayed particles, and mucilage merge and form an “organic soup.”
She defined mucilage as an organic formation, meaning it can be decomposed and broken down by bacteria in both the water column and sediment and return to inorganic matter in the long run. Multiple conditions base the ground for its formation. Climate change and shifting seasons are among the fundamental causes of the problem. For instance, climatic and seasonal alterations or incomplete seasons, such as an extended spring or similar temperatures between winter and spring, can induce mucilage formation. Another reason behind the problem is the water column stagnation due to the absence of the wind affecting the water movement. Therefore, the mucilage gets suspended in the same region and can not scatter around.
Furthermore, nutrient runoff ”primarily nitrogen and phosphorus” from agricultural fields and residential areas enters marine systems through periodic rainfall, significantly contributing to mucilage formation. Nutrient balance also plays a crucial role; when the nitrogen-to-phosphate ratio exceeds 60, dinoflagellates, which promote mucilage growth, outcompete diatoms. Additionally, diatoms require at least 30 µg/L of silica (SiO) to proliferate, making silica availability another key factor in ecosystem stability.
“Ideally, seasonal temperatures should occur at the expected times. Rising sea temperatures in summer are natural and do not create adverse effects, as they contribute to the elimination of mucilage-forming organisms from the system. With increasing water temperatures and a decrease in nutrient levels (such as nitrogen and phosphorus), the growth rate of mucilage-forming organisms slows, preventing the formation of thick mucilage layers,” Büyükateş stated.
“Additionally, changes in wind direction and intensity impact current speeds, affecting the accumulation of mucilage. Previously formed mucilage that sinks to the seafloor is broken down by sediment bacteria, leading to a reduction or disappearance in some regions. Zooplanktonic organisms, fish, and their larvae can also feed on mucilage, potentially leading to an increase in certain species following mucilage events,” she further explained.
Unfortunately, Turkish waters are not unfamiliar with the conception of mucilage. Its first occurrence in Turkey was recorded in the Çanakkale Strait and the Sea of Marmara in 1994. During 2007-2008, the phenomenon was intense lasting for a longer period. However, the Sea of Marmara experienced its most severe mucilage event between March and late June 2021. It disrupted the marine ecosystem and the economic resources of the area until it was eventually alleviated.
Nevertheless, its formation started again in September 2024. First appeared in Erdek Bay and spread to İzmit Bay within 45 days, the mucilage formation has been detected to be between 5 to 25 meters deep. Due to coastal deposition, stagnant water conditions, lack of wind, and above-average sea temperatures, the visibility of mucilage on the sea surface is observed as of late December 2024 and January 2025.
Mucilage formation in the Sea of Marmara is driven by marine pollution, climate change, ecosystem disruptions, excessive nutrients, and weak water circulation. The household, industrial, and agricultural waste discharge generates the accumulation of organic matter and nutrients like nitrogen and phosphorus, creating an environment favoring excessive plankton growth. Rising sea temperatures due to global warming accelerate plankton production while simultaneously reducing oxygen levels, which further fuels mucilage.
The delicate natural balance of the Marmara Sea has been shaped by its connection to the Black Sea and the Mediterranean. Nonetheless, it is being disrupted which contributes to lower oxygen levels at the seabed. This lack of oxygen hinders organic matter from breaking down naturally. Furthermore, the water stagnation combined with reduced natural currents results in mucilage not being carried away. Instead, it particularly lingers along the coast and worsens the problem.
Looking ahead: Will mucilage remain a threat to the Marmara Sea?
According to Büyükateş, climate change, global warming, and shifting seasons should be considered as the new normal. “Research on the potential effects of climate change on Mediterranean marine systems, particularly on mucilage and microbial pathogens, has shown a correlation between mucilage spread and rising surface water temperatures. As long as climate-related impacts persist and sources of pollution (household, industrial, and agricultural wastewater) are not controlled and reduced, the mucilage problem is likely to continue and reoccur in the future,” she stated. However, Büyükateş also remarked that marine systems are dynamic, meaning that if stress factors and threats are removed, the ecosystem can recover and regenerate itself.
Although marine systems are dynamic, the Professor expressed that if the mucilage remains unaddressed, its accumulation on the seabed is long-term, exerting significant pressure on sediment-dwelling organisms. “For example, it can cover bivalve mollusks such as mussels and oysters, as well as sponges, corals, and seagrasses, negatively affecting both oxygen exchange and photosynthesis, ultimately leading to their deaths. Organisms that consume these species and rely on seagrasses for feeding, breeding, and shelter may also disappear from the marine ecosystem as a result. Therefore, in the long term, mucilage can have detrimental effects on the food chain and biodiversity,” Büyükateş said.
However, this is not the only long-term effect of the mucilage. Professor Büyükateş added that the high concentration of solid particles in the water reduces light penetration, negatively affecting photosynthesis. Consequently, suspended particles on the water's surface lead to disruptions in the marine food web, further impacting biodiversity adversely.
Büyükateş also touched upon the rapid microbial breakdown in the water. “Intensive bacterial decomposition occurs, which lowers the amount of dissolved oxygen in the aquatic system below the critical threshold of 5 mg/L-a level below which we do not want oxygen levels to drop. As a result, organisms struggling to survive in this system face mass mortality. Species that can tolerate low oxygen levels and high pollution loads may replace more sensitive species, leading to a decline in biodiversity and ecosystem productivity,” she remarked.
Necessary Measures to Prevent Mucilage
Once the formation process and the effects of the mucilage are understood, long-term solutions to stop and prevent the issue must be considered and hastily implemented. Büyükateş recounted several measures to combat the mucilage. Firstly, she mentioned that the ecosystem must be protected by conserving wetlands, preventing overfishing, controlling coastal erosion, and protecting the habitats. Sustainable agriculture and fisheries are the two critical points in tackling mucilage. Fertilizer and pesticide runoff into marine environments must be reduced alongside encouraging environmentally friendly aquaculture activities.
Though these solutions frame an ideal case, in reality, they might not be immediately fulfilled. Initially, short-term measures such as expanding advanced biological wastewater treatment plants can be implemented to prevent untreated discharges. Regular monitoring of biological, hydrological, and ecological parameters is yet another important step. Finally, like any other problem of society, informing, educating, and raising the awareness of the public on waste management and environmental conservation is essential.
Macro and Micro Attempts to Be Taken
While Büyükateş counted the long-term measures, she also touched upon the critical importance of government authorities’ help in overcoming mucilage. “Government agencies such as municipalities, the Ministry of Environment, Urbanisation and Climate Change the Ministry of Agriculture and Forestry, and the State Hydraulic Works (DSİ) must collaborate on waste treatment, pollution control, and early warning systems,” she remarked.
The esteemed professor highlighted the pressing need for individual responsibility while combating mucilage, emphasizing that alongside the government, citizens must take action. Büyükateş mentioned reducing the use of phosphorus-based synthetic detergents and choosing detergents that dissolve in hot water instead of those that dissolve in cold water are essential. In addition, she highlighted minimizing household and workplace waste, adopting recycling, and raising awareness in our social circles as the key individual steps. She emphasized that the small efforts in contributing to collective change should not be underestimated and that every step either small or large does matter.
Büyükateş referred to the short-term mucilage cleaning methods and long-term prevention strategies that are employed in Türkiye, particularly in the Sea of Marmara. She clarified that both scientists and local authorities are working to make these efforts sustainable. Among the efforts are mechanical cleaning methods including surface cleaning vehicles, nets, and pumping systems to remove mucilage from the sea, and biological methods. Particularly, these biological methods introduce bacteria and enzymes to accelerate natural degradation and restore phytoplankton balance, and chemical methods involving coagulation, sedimentation, and oxygen supplementation to help break down the mucilage. She explained the strengthening wastewater treatment plants as “Advanced biological treatment systems are being implemented to prevent the direct discharge of household and industrial waste into the sea.” Büyükateş further said that projects are being developed to increase underwater currents and movement to prevent mucilage accumulation and spread.
Professor Büyükateş discussed the scientific studies being conducted in Türkiye as part of the fight against mucilage. “One of the most significant initiatives is the Marmara Sea Action Plan Scientific and Technical Committee, established in 2021. Additionally, the Grand National Assembly of Türkiye (TBMM) formed a Research Commission to investigate the causes of the 2021 mucilage outbreak in the Sea of Marmara and to develop solutions. This commission conducted comprehensive studies to examine the causes of mucilage and identify necessary measures,” she said. The commission’s detailed proceedings and reports are published on the official TBMM website to make recommendations publicly available as a guideline for relevant institutions and organizations.
TÜBİTAK Marmara Research Center and various universities are also conducting studies on the pollution load in the Marmara Sea basin, biodiversity impacts, and long-term solutions aiming to provide science-based remedies to protect the marine ecosystem and prevent future mucilage outbreaks.
Though Türkiye has been facing a critical mucilage problem in the Marmara Sea, efforts to mitigate mucilage formation continue. By listening to what experts say about the issue and taking the right science-based steps both individually and collectively, the situation can improved, and the Sea of Marmara can recover to its healthy form.
Edited by: Derya Selin Yener