Off the Mississippi coast, under 1,200 meters of water, a yacht slowly disintegrates. Sea creatures pass, hang and crawl near the wrecked hull, undisturbed for 75 years.
But there is more than we can see in the case of this and other shipwrecks: distinct clusters of microbes inhabit the seafloor around these structures, helping to transform them into artificial reefs full of life.
Shipwrecks are invaders at the bottom of the ocean, but the invasion gradually becomes welcome as several forms of marine life seek refuge between steel and wood.
“Macroscopic animals that inhabit shipwrecks only exist thanks to much smaller life forms,” says Leila Hamdan, a marine microbial ecologist at the University of Southern Mississippi.
That's because microbes like bacteria and archaea line the surfaces in a sticky layer, a bio-film that acts as a chemical and physical attraction for larger creatures, such as barnacles and corals.
Hamdan's team researches how the presence of a shipwreck affects microbial communities. This is a niche study area that covers archeology, biology, ecology and marine sciences. "As far as we know, we are the only ones doing this today."
In September 2018, Hamdan and colleagues left aboard a research vessel and, 110 km offshore, downloaded a remotely operated vehicle to analyze Anona, a shipwreck discovered in the 1990s.
The 35-meter yacht, sumptuously covered in mahogany and teak, with a piano in the lounge, sank in 1944. (The nine-person crew boarded a raft and floated for two days before the rescue.)
The scientists' vehicle contained clear plastic tubes, the size of a water bottle, which plunged into the fine gray sediment of the seabed, at different distances from the hull, to collect material – on the bow, starboard and port side.
Last year, similar fieldwork was done at two other wreck sites in the Gulf of Mexico.
Back in the lab, the team extracted microbial DNA from the nuclei, sequenced the genetic material and found that the seabed microbiome varied according to Anona's distance.
This is something that has not been demonstrated before, according to Hamdan. "A shipwreck materially changes the biodiversity of the seabed."
Near wooden sailboats, scientists have discovered bacteria that degrade cellulose and hemicellulose, some of the main components of the material – perhaps they are feeding on the wreck, according to the team.
The microbiomes of different shipwrecks are also distinct from one another, which raises the question of whether the depth of water plays a role in the microbial community.
It is not known whether these microbes were transported to the bottom of the sea or whether they were there all the time and the conditions became conducive to their flowering after a ship sank.
"That is the $ 1 million question in microbial ecology," says Hamdan.
Translation by Luiz Roberto M. Gonçalves
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