Research into microbial communities on and surrounding deep-sea shipwrecks reveals just how important these lost vessels can be for marine life.
Last year the world was stunned after the first crewed dive in over 14 years revealed brand new images of the wreckage of the Titanic. The two halves of the infamous ship, resting at a depth of 3,810m in Newfoundland, were unrecognisable. The rusting iron hull was not only covered in a thick film of marine life, but it was also slowly disappearing. Researchers explained that specialised metal-eating bacteria and other microbes were slowly but surely transforming the vessel back into its natural components and as a result breathing new life into the area surrounding it. However the titanic is just one example of how the tiniest of organisms can turn sunken ships into biodiversity hotspots.
You may not be able to see them, but our world is teeming with microscopic life and nowhere is that more true than the deep sea. The sediment lining the seafloor is rich in all forms of microbes, including bacteria and archea, which are over 10,000 times more abundant here than in the water above. It has been this way for millions of years, but in the last few hundred it has changed in a big way. That change is of course because of us. The seafloor is now littered with countless new man-made structures that do not naturally belong there, including oil rigs, mining equipment and of course shipwrecks. However these deep-sea intruders are not necessarily unwelcome ones. The complex and chemically rich structures can become building blocks for some of the deep’s most biologically rich communities.
Over time microbes form the seafloor start to cover these invasive structures with a sticky layer of what is known as bio-film. This coating of microscopic life consists of the types of ‘hard-core’ bacteria that can break down metals, wood and other chemically rich compounds and turn them into energy. This energy rich bio-film then attracts slightly larger creatures like barnacles and algae, which in turn bring in the worms, crabs and starfish of the deep. Before too long an entire ecosystem has developed around these structures and turned them into artificial reefs with octopuses, sharks and other top predators. However none of this is possible without the microbes that transform these forgotten objects into bio-available energy.
Exploring the deep
Shipwrecks in particular are excellent candidates for these artificial reefs because they are extremely complex and bring with them a wealth of other objects and substances for microbes to feed on. In the Gulf of Mexico there are over 2,000 known historical shipwrecks spanning over 500 years from the 16th century to WWII. This makes it a perfect place to study this new phenomenon up-close. Step forward Dr Leila Hamden and her research team from the University of Southern Mississippi’s Gulf Coast Research Lab. They specialise in what they call shipwreck microbial ecology. According to Dr Hamden, who recently spoke to the New York Times, “as far as we know, we’re the only ones doing it right now”. The niche area of study spans archaeology, biology, ecology and marine science, but what Dr Hamden and her team are really interested in is the microbes.
Using the research vessel Point Sur the team visit shipwreck sites in the gulf, which they locate using sonar, and explore them using an advanced ROV (remote operated vehicle) called Odysseus. Such as in 2018 when they visited an early 20th century deluxe yacht known as the Anora, which sunk 70 miles off the coast on a voyage to the British West Indies in 1944. As with their normal surveys the ROV took pictures of the marine species living there, as well as collecting samples from its hull to analyse the microbes surrounding it. However this time the team also collected core samples from the seafloor at varying distances surrounding the site. Last year they also repeated this procedure at two other sites involving similar sized yachts from the same time period, all of which had remained intact and upright. The only main difference between them was their respective depths.
At the recent 2020 Ocean Sciences Meeting in San Diego, Dr Hamden revealed some very interesting results about what they had found at these sites. Upon analysing the abundance and diversity of microbes in each of the samples they realised two things. Firstly the microbe communities changed with distance from the wreckage. The highest number of different microbes was found between 160-330 feet away from the actual ship, something Dr Hamden says was expected because “resources begin to spread over time”. Whereas on the actual vessel there were higher concentrations of just a few species of bacteria, those that degrade cellulose found in wood. This shows that the microbial communities in shipwrecks are much more dynamic and spatially complex than previously thought.
The second thing they discovered was that these complex communities were also significantly different between the sites, even though the only thing separating them was depth. This was a much more surprising finding for the team and suggests that location is an important factor in how these artificial habitats develop. Combined with the fact that other shipwrecks differ greatly in size, shape, materials and time left on the seafloor, it suggests that no two microbial communities will likely be the same. This is an important development because it means that every shipwreck in our oceans, of which there are tens if not hundreds of thousands, could be capable of sustaining its own unique ecosystem. Meaning we have created thousands of isolated underwater islands scattered across the seafloor and full of life.
What makes them so unique?
The teams new discovery raised the question of how the microbial communities surrounding shipwrecks could be so different, when all that was changed was their depth. Do different microbes get transported to different depths, or are they all present on the seafloor and just prefer different depths? “That is the million dollar question” says Dr Hamden, who is now looking into this very topic. She suspects that it is probably the latter and that all deep-sea microbes can be found at every site, but that the conditions of each site will determine which species thrive and which take a back seat. Whilst depth is the main difference between sites, this also means conditions like temperature, pressure and salinity could also contribute.
Isolated but not invulnerable
These newly formed shipwreck habitats are not just a fascinating area of research for Dr Hamden and her team. They are also becoming key ecosystems that provide life in the deep-sea with an abundance of energy and nutrients in waters that never see the light of day. Their individuality by isolation could be crucial in maintaining biologically diverse and rich oceans that are already suffering in this department due to human caused issues. However ironically these man-made habitats, responsible for undoing man-made problems, are themselves facing man-made threats as well.
In 2014 Dr Hamden and her colleagues were also part of a study, alongside the Bureau of Ocean Energy Management in New Orleans, that showed these new habitats are particularly susceptible from oil spills. After the Deepwater Horizon disaster, where 4 million barrels of oil were released into the ocean, oil was found to impede the ability of microbial communities to develop on nearby shipwrecks. It is hardly the most important impact of major oil spills like this one, but it just goes to show that the more we pollute and invade in the marine world, the more unforeseen effects we will have.