Abandoned WWII Shipwreck Has Altered The Ocean's Microbiology For 80 Years

NATURE18 October 2022

ByDAVID NIELD

Torn deck plating of the V-1302 John Mahn shipwreck. (VLIZ)

There's a certain romance and mystique associated with shipwrecks when seen as ancient artifacts hiding in the gloom. Where we might imagine untold treasures locked behind their rusting hulls, in reality it's often a mess of old fuel, corroded bombs, and toxic waste.

A new study analyzing the World War II shipwreck V-1302 John Mahn, in the Belgian part of the North Sea, has found substances leaking from the old wreck are still influencing the surrounding microbiology and geochemistry some 80 years after the ship sank to the sea floor.

Considering there are thousands of similar wrecks in the North Sea alone, the cumulative impact on marine life is potentially huge – especially considering the munitions and hazardous materials that are often stored on military vessels.

"We wanted to see if old shipwrecks in our part of the sea were still shaping the local microbial communities and if they were still affecting the surrounding sediment," says microbial ecologist Josefien Van Landuyt, from Ghent University in Belgium. "This microbial analysis is unique within the project."

The V-1302 John Mahn started out as a German fishing trawler before being converted into a patrol boat during the war. It was sunk close to the Belgian coast in 1942 by the British Royal Air Force, as part of the Channel Dash operation.

Researchers took samples of the steel hull and the sediment at twelve different points close to the wreck and at increasing distances away from it, to see how far any possible contamination might be spreading.

The concentration of toxic pollutants around the vessel varied depending on distance: there was evidence of heavy metals (like nickel and copper), arsenic, explosive compounds, and polycyclic aromatic hydrocarbons or PAHs (chemicals that occur naturally in coal, crude oil and gasoline).

As might be expected, concentrations of these pollutants increased with proximity to the ship. The highest metal concentrations were found in the sample closest to the ship's coal bunker, for example.

These concentrations impact the surrounding microbial life, the researchers found. Microbes such as Rhodobacteraceae and Chromatiaceae, known to degrade PAHs, were found in the samples that had the highest concentrations of pollutants. Sulfate-reducing bacteria was found on the hull, most likely corroding it.

"Although we don't see these old shipwrecks, and many of us don't know where they are, they can still be polluting our marine ecosystem," says Van Landuyt.

"In fact, their advancing age might increase the environmental risk due to corrosion, which is opening up previously enclosed spaces. As such, their environmental impact is still evolving."

The researchers suggest that there's much more to discover in terms of the influence of shipwrecks on underwater ecosystems – yet another example of how human activity is changing the natural world around us.

Work continues to discover what shipwrecks can teach us about the past and how they're affecting the oceans in the present – and the team behind the current study is keen to use the same techniques on other shipwrecks in the area.

"The general public is often quite interested in shipwrecks because of their historical value, but the potential environmental impact of these wrecks is often overlooked," says Van Landuyt.

"We only investigated one ship, at one depth, in one location. To get a better overview of the total impact of shipwrecks on our North Sea, a large number of shipwrecks in various locations would have to be sampled."

The research has been published in Frontiers in Marine Science.

 

Scientists Track Eels to Their Ocean Breeding Grounds in World-First

NATURE19 October 2022

ByCLARE WATSON

A European eel emerges from sand.

After generations of speculation, scientists have finally managed to track European eels the entire way back to their breeding grounds in the Sargasso Sea – following their movements thousands of kilometers along what is considered one of the most impressive animal migrations in nature.

Scientists are gushing with excitement because this is the first direct evidence of a long-suspected part of the eels' life cycle that was proposed almost 100 years ago.

Until now, no eggs or eels had been found in the North Atlantic Ocean's Sargasso Sea confirming this truly is where eels gather to breed.

"Eels have piqued the curiosity of scientists for millennia," study author and fish biologist Kim Aarestrup of the Technical University of Denmark said on Twitter.

"For the first time ever, we followed eels to their spawning grounds."

Way back in the early 1920s, Danish biologist Johannes Schmidt discovered eel larvae in the Sargasso Sea, far from their freshwater, estuarine, and coastal habitats in Europe and Africa.

Publishing his results in 1923, Schmidt foreshadowed the next century of research to understand how eels reproduce, describing his efforts as "disappointment alternating with encouraging discoveries and periods of rapid progress with others during which the solution of the problem seemed wrapped in deeper darkness than ever."

In the decades since, scientists have been trying to trace the line back to where eels go to breed – a task made harder by the many obstacles in the eels' way: dams, weirs, pollution, habitat loss and overfishing. A sharp decline in European eel (Anguilla anguilla) numbers since the 1980s has only made the task all that much harder, and more urgent.

But don't underestimate these enigmatic creatures. European eels migrate between 5,000 and 10,000 kilometers (3,100 to 6,210 miles) to spawn at sea, after which their larvae drift back towards land and the relative safety of rivers.

Using satellite tags, the researchers behind this latest discovery obtained tracking data from 21 female European eels as they navigated the last leg of their epic journey, southwest from the Azores, a volcanic archipelago in the North Atlantic Ocean, far west of Portugal.

Past research tracking eel migrations had shown eels from all over Europe converge around the Azores islands before departing for the Sargasso Sea, an ocean region bounded by four swirling ocean currents and named for its vast forests of Sargassum seaweed.

The eels were captured, tagged with detachable satellite trackers, swabbed for DNA testing, and released back into the Atlantic Ocean from the Azores islands back in 2018 and 2019.

Six eels reached the Sargasso breeding grounds months later with their satellite trackers still attached; data from 15 other eels were collected along the way. The longest recorded straight-line distance was 2,275 kilometers (1,410 miles).

"Their journey will reveal information about eel migration that has never been known before," says fisheries biologist Ros Wright of the UK Environment Agency, who led the study.

It's still unclear how the eels find their way to the Sargasso Sea or even how long their spawning season extends.

The swimming speed of the eels in this study, which averaged 6.8 kilometers (4.2 miles) a day, and the length of their marathon journey – which takes more than a year – suggests these long-haulers need to make a very calculated migration.

"Rather than make a rapid migration to spawn at the earliest opportunity, European eels may instead make a long, slow spawning migration at depth that conserves their energy and reduces mortality risk," Wright and team write in their published paper.

"This timing would enable the completion of their reproductive maturation before they arrive at the spawning area."

"It's also incredible to know they go way deeper than 1,000 meters on the way!" James Maclaine, a senior fish curator at the UK National History Museum, tweeted. That's plunging more than 3,280 feet down into darkness.

But questions remain over the eels' timing and navigation across thousands of kilometers in open ocean to reach the Sargasso Sea.

It could be that they sense Earth's magnetic fields like Chinook salmon (Oncorhynchus tshawytscha), which return to the exact stream where they hatched. Sniffing out olfactory cues or following ocean currents or temperature fronts are other possibilities, too.

While it might be a while yet before we untangle those threads, for now, this new study completes the map of eel migrations, placing the Azores at the center of conservation efforts to combat the eels' decline.

"This discovery emphasizes the role of the Azores in the life cycle of eels," says study author and fish ecologist José Manuel N. Azevedo from the University of the Azores.

"It will help scientists and conservationists to push for measures to restore eel habitats across the archipelago."

The research was published in Scientific Reports.