Shipwrecks under the microscope: feeding the deep

Abstract

The sediment of the deep sea is one of the largest ecosystems on the planet and also one of the least explored. The lack of light, high pressure and low temperature mean that only specialised organisms can inhabit these areas. These include microbes, often relying on any form of sustenance they can get, and what starts as just a cluster can form the base of biodiverse communities. Examples of deep-sea microbial hotspots include the areas around whale carcasses, which have been reasonably well studied, and wooden-hulled shipwrecks, both of which provide nutrition, a safe place to hide and surfaces to be colonised. However, the sites of shipwrecks have rarely been examined under the microscope. Justyna Hampel and colleagues from the University of Southern Mississippi, USA, and the US Bureau of Ocean Management examined two wooden-hulled deep-sea shipwrecks in the northern Gulf of Mexico: one relatively shallow (∼525 m) and one deep (∼1800 m), both from the late 19th century.To describe the microbial ecosystems in the sediment surrounding the two historic sites, the authors used a remotely operated vehicle to take samples of the sediment at distances from 4 to 60 m along and out from each wreck. The team then extracted and sequenced DNA from any organisms that they collected in the sediment cores to find out what lifeforms were there. Finally, they analysed the differences between the microbial communities at the two shipwreck sites.The team found the greatest microbiome diversity at the site of each shipwreck, decreasing the farther they moved away from it. They also discovered that the shipwrecks have a larger than expected influence on the local microbiology, with distinctive and unique core microbiomes at the two wreck sites. In addition, the presence of the shipwreck changed the availability of nearby tasty elements, such as nitrogen and carbon, that microbes can convert into food for larger organisms. However, the two wrecks affected the seabed in their respective areas in different ways, and the scientists think that this is largely due to differences in shipwreck depth, as well as their proximity to the mouth of the Mississippi river (∼30 km and ∼100 km), washing nutritious material from the land out to sea. Essentially, shipwrecks play a role in supplying deep-sea ecosystems with sustenance to an extent similar to that of other dead material from above, such as whale carcasses.The authors conclude that wooden shipwrecks not only serve to provide refuge and surfaces for organisms to colonise but also are a significant and long-term source of the building blocks upon which diversity can flourish in a setting short of nutrients and far from the shore. Recent surveys of the seafloor in this area of the Gulf of Mexico have identified what appear to be many more nearby shipwrecks with depths in excess of 1000 m that have yet to be surveyed. These unexplored and unidentified sites can undoubtedly tell us more about the ecology of deep-sea microbes and how the arrival of structures made by humans changes the microbial diversity and composition of the seafloor.