An international team of scientists around Tanja Stratmann from the Max Planck Institute for Marine Microbiology in Bremen, Germany, and Utrecht University, the Netherlands, and Daniëlle de Jonge from Heriot-Watt University in Edinburgh, Scotland, has investigated the food web of the deep seafloor to see how it is affected by disturbances such as those caused by mining activities.
For this, the scientists travelled to the so-called DISCOL area in the tropical East Pacific, about 3000 kilometres off the coast of Peru. Back in 1989, German researchers had simulated mining-related disturbances in this manganese nodule field, 4000 metres under the surface of the ocean, by ploughing a 3.5 km wide area of seabed with a plough-harrow. “Even 26 years after the disturbance, the plough tracks are still there,” Stratmann described the site. Previous studies had shown that microbial abundance and density had undergone lasting changes in this area. “Now we wanted to find out what that meant for carbon cycling and the food web of this deep ocean habitat.”
“We looked at all different ecosystem components and on all levels, trying to find out how they work together as a team,” de Jonge explained who carried out the project as part of her Master’s Thesis at the NIOZ Royal Netherlands Institute for Sea Research and the University of Groningen, The Netherlands. The scientists quantified carbon fluxes between living and non-living compartments of the ecosystem and summed them up as a measure of the “ecological size” of the system.
They found significant long-term effects of the 1989 mining simulation experiment. The total throughput of carbon in the ecosystem was significantly reduced. “Especially the microbial part of the food web was heavily affected, much more than we expected,” said Stratmann. “Microbes are known for their fast growth rates, so you’d expect them to recover quickly. However, we found that carbon cycling in the so-called microbial loop was reduced by more than one third.”
The impact of the simulated mining activity on higher organisms was more variable. “Some animals seemed to do fine, others were still recovering from the disturbance. The diversity of the system was thus reduced,” said de Jonge. “Overall, carbon flow in this part of the food web was similar to or even higher than in unaffected areas.”