More marine life is living on some World War II munitions disposed of on the Baltic Sea's seabed than on the sediment surrounding it. The findings, reported in a paper in Communications Earth & Environment, show that some marine organisms can tolerate high levels of toxic compounds if there is a hard surface for them to inhabit. The results also demonstrate how detritus from human conflict can provide habitats for wildlife, which is similarly shown in a Scientific Data study mapping a fleet of World War I shipwrecks in Maryland, USA.
Prior to the signing of the 1972 London Convention on the Prevention of Marine Pollution, explosive munitions were frequently disposed of by dumping them unused at sea. These munitions typically contain chemicals which are highly toxic to marine life, although the hard metal casings may provide a suitable surface for marine life to live on.
Andrey Vedenin and colleagues used a remotely controlled submersible to investigate a newly-discovered munitions dumpsite in Lübeck Bay in the Baltic Sea in October 2024. They filmed the munitions and analysed water samples collected from the site, and also investigated two areas of the surrounding sediment for comparison.
The authors identified the discarded munitions as warheads from V-1 flying bombs, a type of early cruise missile used by Nazi Germany in late World War II. They found that there was significantly more marine life present on the munitions than the sediment — an average of around 43,000 organisms per square metre compared to around 8,200 organisms per square metre. Similar magnitudes of marine life abundance have been recorded on natural hard surfaces in the bay in other studies. The concentrations of explosive compounds (mostly TNT and RDX) in the water varied widely, from as little as 30 nanograms per litre to as much as 2.7 milligrams per litre — a level estimated to be potentially fatally toxic to marine life.
The authors suggest that, compared to the surrounding sediment, the advantages of living on the hard surfaces of the munitions outweigh the disadvantages of the chemical exposure. They note that organisms were mainly observed on the casings rather than uncovered explosive material, and speculate that this may have reflected lifeforms trying to limit their chemical exposure. However, the authors conclude that although the munitions are currently an important habitat in the bay, replacing them with a safe artificial surface would further benefit the local ecosystem.
In a separate study, published in Scientific Data, David Johnston and colleagues present a high-resolution photographic map of all 147 wrecks currently in the so-called "Ghost Fleet" of Mallows Bay, on the Potomac River, Maryland, USA. These ships were built during World War I but were deliberately burnt and sunk in the late 1920s, and their wrecks are now known as a habitat for a wide variety of wildlife, such as ospreys (Pandion haliaetus) and Atlantic sturgeon (Acipenser oxyrinchus). The authors created the map by combining high-resolution photographs (an average of 3.5 centimetres per pixel) of the entire fleet, taken using aerial drones in 2016. They suggest that the map may be useful for future archaeological, ecological, and cultural research into the fleet.
