JPI Oceans - Deep Sea Mining - Assessing ecosystem functioning in the DISCOL site 26 years after disturbance

This is one of the few studies that investigate ecosystem function in an abyssal plain that was previously disturbed by a mimicked deep-sea mining experiment. Despite the low number of replications, the results indicate that the processing of fresh phytodetritus has not fully recovered after 26 years as the uptake of fresh phytodetritus by bacteria, nematodes and holothurians is significantly lower in plow tracks compared to reference sites. Furthermore, the deployment of large (0.25 m2) benthic incubation chambers allowed to determine the role of holothurians in the uptake of phytodetritus and showed that their uptake is highest compared to the other metazoans (meiofauna, macrofauna). The analysis of size-class dependent uptake of the phytodetritus resulted in a higher biomass-specific uptake of phytodetritus for holothurians than for nematodes implying that for the metabolism of holothurians phytodetritus is relatively more important than for the metabolism of smaller size classes. Additionally, the elevated C:N-ratios of incorporated phytodetritus in nematodes and macrofauna relative to their tissue C:N ratio let us speculate that these benthic organisms are likely more carbon than nitrogen limited at this particular study site

During the RV Sonne cruise 242-2, IRIS will investigate (with JPI-Oceans Mining Impact project partners NIOZ and the University of Gent) how the impact of mechanical disturbance of the sediment (from a stimulated mining event) affects the food web and changes the processing or cycling of organic matter in the sediment ? a key function of benthic ecosystems. The experiments will be conducted in the DISCOL area of the eastern Pacific ocean. We will use a stable isotope pulse chase approach in which 13C/15N labeled algae will be added to the sediment along the disturbance gradient at the DISCOL area (see above). We will monitor the uptake and assimilation of these algae by all food web components including microbes and animals of all size classes (meio-, macro- and megafauna) and the conversion to inorganic carbon (DIC) upon remineralization. These experimental data in combination with biomass assessments made in WP2 of the JPI-Ocean Mining Impact project will be integrated using food-web modeling to add to our knowledge on the functioning of deep-sea ecosystems, and changes that are expected following deep-sea mining disturbance.