A thick, jelly-like layer of marine mucilage has once again returned to Turkey’s Marmara Sea, posing a severe threat to coral colonies and marine biodiversity, marine scientists have warned. The alarming development was confirmed by İstanbul University marine biologist Assoc. Prof. Nur Eda Topçu Eryalçın, who called the phenomenon “a nightmare come back”, speaking to Anadolu Agency on Wednesday.
Although the outbreak is not as visible on the surface as during the infamous crisis of 2021, researchers have now documented heavy mucilage layers on the seabed, especially around the coral-rich regions near the Princes’ Islands, Marmara Island, and Avşa Island.
“We’re seeing large mucilage chunks in the water column, and now, unfortunately, it’s also densely covering the sea floor,” said Topçu Eryalçın, who leads a team that regularly monitors coral ecosystems in the area. “If this trend continues, we may soon witness a sea devoid of living organisms.”
Often called “sea snot” by the public, mucilage is a thick organic substance formed by the excessive growth of phytoplankton, stimulated by warmer sea temperatures, pollution, and stagnant waters. Once it settles on the sea floor, it reduces oxygen levels and light penetration, suffocating marine life and accelerating coral death.
Marmara Sea corals, most of which reside between 30 to 40 metres deep, are already showing signs of damage. “We observed necrotic degradation on delicate coral branches, especially in the southern parts of the sea,” Topçu Eryalçın reported, adding that some endangered species had also been affected.
The return of mucilage highlights the ongoing threat posed by untreated sewage discharge, industrial pollution, and the worsening impacts of climate change. Despite a government action plan announced after the 2021 outbreak, many of its measures remain unimplemented.
“The Marmara is a fast-responding sea,” Topçu Eryalçın said. “If we act decisively and sincerely—especially by stopping untreated wastewater—there is still hope. But the clock is ticking.”
Experts urge immediate upgrades to wastewater treatment, stricter pollution control, and broader climate action to prevent the sea’s ecosystem from spiralling into collapse.
