From metabarcoding time series to plankton food webs: The hidden role of trophic hierarchy in providing ecological resilience

The advent of metabarcoding (metaB) in aquatic ecology has provided a huge amount of information on plankton biodiversity worldwide. However, the large datasets obtained with that approach are still partially explored, especially for what concerns the study of trophic interactions and food webs. In this study, we analysed a metaB time series from the Long-Term Ecological Research station MareChiara (LTER-MC) in the Gulf of Naples, Mediterranean Sea, Italy, to describe the link between plankton diversity and food-web structure. We derived co-occurrence networks from metaB time series, identified putative trophic interactions among co-occurrences based on biological information (body size and trophic habit) available for planktonic organisms detected by metaB, and converted co-occurrence networks into conceptual models of food webs. The latter showed structural properties resembling ecological processes, because network modularity (the presence of semi-independent sub-networks) paralleled trophic hierarchy (the dimensional difference between predator and prey). We also analysed the role of planktonic organisms in maintaining network modularity. The largest predators occupied distinct modules, suggesting niche partitioning, whereas the smallest preys worked as fundamental connectors between larger predators (and different modules). Overall, the presence of trophic hierarchy and modularity shown herein supports the view of the high ecological resilience of plankton, pursued via food-web rewiring, to environmental shifts.