As Germany demilitarized after World War II, it dumped massive amounts of its leftover munitions into the Baltic Sea. A recent study has found that some of those submerged weapons, which are still releasing toxic compounds, now host more marine organisms than the sediments around them.
In October 2024, researchers used a remotely operated vehicle (ROV) equipped with two camera systems to investigate a munition dumpsite located in the northern part of Lübeck Bay, in the southwest of the Baltic Sea. On the seafloor, scattered across the fine mud sediment, they found large metal cylinders that they identified as discarded warheads from Fieseler Fi103 cruise missiles used by Nazi Germany during the war.
To see what organisms lived at the site, the researchers recorded videos using the ROV, and collected biological and sediment samples from both the military debris and the surrounding sediment.
They identified eight species in the ROV videos, including snails, sea anemones, worms, starfishes, crabs, and fish including Atlantic cod, black goby and flounder. The most abundant species were Polydora ciliata worms and Metridium dianthus sea anemones.
The missile debris supported more organisms overall — 43,184 individuals per square meter (4,013 individuals per square foot) — compared to the surrounding sediment that had 8,213 individuals/m2 (763 individuals/ft2).
“We were prepared to see significantly lower numbers of all kinds of animals. But it turned out the opposite,” study author Andrey Vedenin, from the Senckenberg Research Institute in Germany, told ABC news.
The researchers also found that the waters around the munitions contained highly toxic explosive compounds, mainly TNT and RDX, sometimes at levels known to be hazardous to marine life. This suggests the high concentrations of explosive compounds “are not sustained long-term, or that they, in fact, do not have a major negative effect on nearby organisms,” the authors write.
Additionally, the study found that most organisms were concentrated on the metal parts, while the bare explosive filling was largely barren, indicating that the animals avoid colonizing the heavily contaminated surfaces, the authors note.
The findings suggest that despite the toxic risks that munitions can pose to marine life, the metal surfaces have created a valuable hard substrate habitat in a largely soft-bottomed sea.
Glacial stones and boulders were once common at the bottom of the German Baltic Sea, the researchers add, but the historical practice of “stone-fishing” for construction and commercial use largely removed them. Stone-fishing became illegal in 1976, but by then much of the original habitat had been lost.
The researchers suggest that in the future, hazardous munitions on the seafloor should be replaced with safe hard objects to recreate natural conditions for native wildlife.
Banner image: Starfish on sunken World War II munitions in the Baltic Sea. Image courtesy of Vedenin et al., 2025 (CC BY 4.0).
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