Composite image, or orthomosaic, of the wreck of Benzonia lying partially on top of the wreck of Caribou, in the “Ghost Fleet” of World War 1 shipwrecks in Mallows Bay, USA. Credit: Duke Marine Robotics and Remote Sensing Lab
Two recently published studies showcase how underwater human structures can become essential habitats for marine life, with discarded munitions and ships from the World Wars now home to vibrant ecological communities.
The first study found that more marine life lives on World War II munitions on the Baltic Sea floor than on the surrounding sediment. Some of the marine organisms can tolerate the high levels of toxic compounds leaking from the unexploded bombs, as long as there is a hard surface for them to live on.
In a separate study, published in Scientific Data, researchers from Duke University’s Marine Robotics and Remote Sensing lab mapped a “Ghost Fleet” of World War I shipwrecks which have become habitat for a variety of wildlife, such as ospreys.
“For the first time, the composition and structure of epifauna on the surface of marine munitions are described,” write the authors of the first study, which has recently been published in Communications Earth & Environment. Epifauna refers to sea creatures that live on the seafloor.
Unused explosive munitions were often disposed of by dumping them at sea prior to the signing of the 1972 London Convention on the Prevention of Marine Pollution. The team used a remotely controlled submersible to examine a dumpsite in Lübeck Bay in the Baltic Sea to investigate the impact the munitions have had on marine environments.
The remotely controlled submersible Käpt’n Blaubär being inspected on the deck of RV Alkor during the research cruise AL628, March 2025. Credit: Ilka Thomsen, GEOMAR
Only 2 of the 9 objects examined were intact. The other 7 were in varying stages of degradation, which meant the explosive chemicals were exposed.
They identified the munitions as being from discarded warheads from V-1 flying bombs which were used by Nazi Germany in the late stages of World War II. Concentrations of the explosive compounds, mainly TNT and RDX, were found to vary between 30 nanograms and 2.7 milligrams per litre in the surrounding water.
Despite this, an average of about 43,000 organisms per square metre (m2) were found living on the munitions, with only 8,200 organisms per m2 on natural sediment nearby.
“On the individual objects,” write the authors, “the majority of epifauna was found on metal carcasses, while the exposed explosive was usually free of visible overgrowth.”
These results suggest the advantages of living on the surfaces of munitions outweigh the potential exposure to explosive and toxic chemicals for many marine organisms.
“This suggests that the high measured explosive chemical concentrations are not sustained long-term, or that they, in fact, do not have a major negative effect on nearby organisms,” the authors write.
“Overall, the epifaunal community on the dumped munition in the study area reaches a high density, with the elevated metal structures providing a suitable habitat for benthic organisms.”
While the munitions seem to be an important habitat for this local ecosystem, the researchers suggest replacing them with a safer artificial surface that does not contain explosives to further benefit marine life.
Composite image of the entire “Ghost Fleet” of Mallows Bay, with individual wrecks labelled. Credit: Duke Marine Robotics and Remote Sensing Lab
In the second study, a team of researchers conducted aerial surveys to capture images of 147 abandoned World War I steamships at Mallows Bay on the Potomac River in Maryland, USA. It is the largest known shipwreck in the Western Hemisphere.
“Since their arrival, the ships have become an integral part of the ecology at Mallows Bay,” write the authors.
“However, sea level rise, sediment infill, plant colonisation, and physical deterioration are changing the nature of these shipwrecks over time.”
Like the previous study, the researchers found a variety of creatures have made the shipwreck their home. One of the species includes the endangered Atlantic sturgeon, which uses the ship as its nursery.
As the “Ghost Fleet” shipwrecks become islands, they are shaping both the coastal and aquatic habitats of Mallows Bay. The “Three Sisters” are pictured in the bottom right. Credit: Duke Marine Robotics and Remote Sensing Lab
The authors are hopeful their map will be an insightful resource for future ecological and archaeological research into the area.
“These data and products will enable researchers to monitor and study the changing terrestrial and aquatic ecosystems,” write the authors.
“The use of unoccupied aircraft systems allows for the creation of detailed orthomosaics and digital surface models, which provide valuable baseline data for archaeological, geological, and ecological assessments.”