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

Abstract

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.

The Gulf of Naples as a model system for plankton ecology studies

“…A whole range of classical and advanced approaches were used to address plankton variability, including the analysis of physical-chemical, biological and diversity data from the natural environment (Kokozska et al, 2023;Mazzocchi et al, 2023;Romillac et al, 2023;Zingone et al, 2023), laboratory experiments (e.g., Carotenuto et al, 2023;René et al 2023;Traboni et al, 2023) and more sophisticated chemotaxonomic (Saggiomo et al, 2023) and biomolecular approaches (Di Capua et al, 2023;Mordret et al, 2023;Russo et al, 2023). The latter studies have addressed temporal trends in groups of species hardly detected by morphological studies, unveiling, for example, a high amount of dinoflagellate diversity not assigned to any described taxa (Mordret et al, 2023).…”

Inferring species interactions from co-occurrence networks with environmental DNA metabarcoding data in a coastal marine food-web

“…Current estimates suggest between a quarter and half of co-occurrences in networks could be trophic in origin. However, these have been primarily estimated using putative trophic interactions for plankton data, which are not well resolved, or using presence-absence datasets (Freilich et al, 2018; Russo et al, 2023; Russo et al, 2022). Detecting trophic interactions in co-occurrence networks is particularly challenging as they exhibit strong spatial dependency resulting in either positive or negative co-occurrences (Cazelles et al, 2016; Russo et al, 2023; Thurman et al, 2019).…”

“…However, these have been primarily estimated using putative trophic interactions for plankton data, which are not well resolved, or using presence-absence datasets (Freilich et al, 2018; Russo et al, 2023; Russo et al, 2022). Detecting trophic interactions in co-occurrence networks is particularly challenging as they exhibit strong spatial dependency resulting in either positive or negative co-occurrences (Cazelles et al, 2016; Russo et al, 2023; Thurman et al, 2019). Negative co-occurrences are expected at finer scales where prey are successfully avoiding predators, whilst positive co-occurrences over greater scales indicate predators tracking their prey (Thurman et al, 2019).…”

Cryptic species in time and space: an assessment of cryptic diversity within eight nominal species of Hydrozoa (Cnidaria)

“…This is true in the marine environment, especially for planktonic marine invertebrates. Planktonic communities are highly variable on a temporal scale [ 1 ]. Frequent and long-term sampling is crucial to understanding their ecological and temporal dynamics and essential for estimating biodiversity patterns.…”

“…Cosmopolitan nominal species have often been shown to be complexes of local cryptic species with allopatric ranges. However, planktonic species that are morphologically indistinguishable and inhabit the same locality, but show different seasonality have received little to no attention due to the dense long-term sampling that is needed to discover them [ 1 ].…”