Shipwrecks do more than cut short lucrative deals – they also alter the microbial communities of the seabed, at least in the case of wooden ships.
A new study by researchers at the University of Southern Mississippi reports that historic wooden shipwrecks produced local changes in microbial communities on the sea floor where they lay. The millions of such shipwrecks scattered across the world’s oceans each create a potentially unique habitat and micro-ecosystem for different strains.
These findings, the team says, are the first evidence of the impact of human structures on the distribution of microbes on the seabed.
“Knowing and understanding microbial communities is important because they provide early and clear evidence of how human activities are changing life in the ocean,” said corresponding author Dr Leila Hamdan of the University of Southern Mississippi. “Oceanologists know that hard natural habitats, some of which have been present for hundreds or thousands of years, shape the biodiversity of life on the sea floor.”
“This work is the first to show that built habitats (places or things made or modified by humans) also impact the films of microbes (biofilms) that cover these surfaces. These biofilms are ultimately what allow harsh habitats to turn into islands of biodiversity.
Much like natural geological features on the seabed, wooden shipwrecks create habitats that deep-sea microbes can inhabit. While we knew that wooden shipwrecks could harbor impressive communities of macroscopic life inside the hulls of ancient ships, we had very little data on the microbes that also inhabit these structures.
Since microbes are at the base of ocean food chains, understanding how man-made structures (including shipwrecks) can impact their diversity can teach us a lot about how to better protect the oceans. According to UNESCO estimates, there are up to three million shipwrecks in the world, most of which are wooden.
To better understand the local effect of shipwrecks, the team worked on two sites, the wrecks of wooden sailboats that sank in the Gulf of Mexico in the late 19th century.
UNESCO estimates that there are up to three million shipwrecks in the world, most of which are wooden. As the first study of microbial life around these sites, Hamdan and his collaborators chose two wooden sailing ships that sank in the Gulf of Mexico in the late 19th century. Samples were taken from these sites by placing pieces of pine and oak wood at different distances (0-200 meters) from the wrecks and leaving them there for four months. After recovery, these pieces of wood were analyzed for their content of bacteria, archaea and fungi using genetic sequencing.
The type of wood used had the greatest impact on the diversity of bacteria seen in the microbial samples – oak was more palatable to these little creatures than pine – although it had a much smaller influence on the diversity of archaea and fungi.
Meanwhile, the greatest influence on the overall diversity of species identified in the samples was proximity to the site. Surprisingly, however, it was not those closest to the wrecks that showed the greatest variety, but those within about 125 meters of the downed ships.
Overall, the team explains that the presence of shipwrecks has a significant impact on the microbial richness of their surrounding area, with significant changes in biofilm composition and dispersion. Environmental factors such as depth and local nutrient availability also influenced the behavior of biofilms at the site of a shipwreck, the team adds.
Although the current article focuses on wooden shipwrecks, the authors note that many man-made underwater structures today are made of metal – oil and gas platforms or pipelines, for example, are scattered in the whole world. Further research will also be needed to understand the impact of such a structure.
“While we are aware that human impacts on the seabed are increasing due to multiple economic uses, scientific discovery does not track how this shapes the biology and chemistry of underwater natural landscapes,” Hamdan said. “We hope this work will initiate a dialogue that will lead to research into how built habitats are already altering sea depths.”
The article “Historic Wooden Shipwrecks Influence Dispersal of Deep-Sea Biofilms” has been published Marine Science Frontiers.