Stable isotopes (¹⁵N) facilitate non‐invasive labelling of large quantities of macroinvertebrates across different species and feeding types

Abstract

While macroinvertebrate dispersal operates at the individual level, predictions of their dispersal capabilities often rely on indirect proxies rather than direct measurements. To gain insight into the dispersal of individual specimens, it is crucial to mark (label) and capture individuals. Isotopic enrichment with 15N is a non‐invasive method with the potential of labelling large quantities of macroinvertebrates. While the analysis of 15N is widely utilised in food web studies, knowledge on the specific utility of isotopic enrichment with 15N for mass labelling of macroinvertebrate individuals across different taxa and feeding types is limited. Previous studies have focused on single species and feeding types, leaving gaps in our understanding of the broader applicability of this method. Therefore, this study aimed to test and compare isotopic mass enrichment across several macroinvertebrate taxa and feeding types. We released 15NH4Cl at five stream reaches in North‐Rhine Westphalia, Germany, and successfully enriched 12 distinct macroinvertebrate taxa (Crustacea and Insecta). Significant enrichment was achieved in active and passive filter feeders, grazers, shredders and predators, and predominantly showed positive correlations with the enrichment of the taxa's main food sources phytobenthos and particulate organic matter. Enrichment levels rose rapidly and peaked at distances between 50 m and 300 m downstream of the isotopic inlet; significant enrichment occurred up to 2000 m downstream of the isotopic inlet in all feeding types. Macroinvertebrate density estimates on the stream bottom averaged to a total of approximately 3.4 million labelled individuals of the 12 investigated taxa, thus showing the high potential of isotopic (15N) enrichment as a non‐invasive method applicable for mass labelling across different macroinvertebrate feeding types. Hence, isotopic enrichment can greatly assist the analysis of macroinvertebrate dispersal through mark‐and‐recapture experiments, as it allows to measure the movement at the level of individual specimens.

Contributions of source populations, habitat suitability and trait overlap to benthic invertebrate community assembly in restored urban streams

“…Passive aerial dispersal is also possible for hololimnic species, e.g., via phoresy (Figuerola & Green, 2002;Van Leeuwen et al, 2013). Hence, taxa could have entered the Boye system from a 22 neighbouring stream network, e.g., the Rotbach or Schwarzbach (Enss et al, 2024). Both streams are in near-natural conditions and could act as potential source populations for the Boye system (Winking et al, 2016).…”

Drivers of recovery and degradation of riverine benthic macroinvertebrate communities: A nationwide analysis of time series

“…A recent case study by Gillmann et al (2024a) on a restored catchment provided initial evidence supporting the ARC, highlighting the importance of species' dispersal capacity and increasing interspecific competition during recovery, as well as a decrease in the present species' tolerance to organic pollution with increasing recovery. Further studies by Enss et al (2024) and Gillmann et al (2024b) emphasized the relevance of dispersal. However, the role of biotic interactions, especially competition, remains unclear beyond the initial insights from Gillmann et al (2024a), which were limited to one catchment with eleven sampling sites.…”

“…However, the response of biota is often weaker than the level of improved conditions would suggest (Lorenz et al, 2018). Reasons for the delayed or even absent biotic recovery may be related to remaining stressor impacts (Brettschneider et al, 2019), or to biotic constraints such as dispersal capacity (Sundermann et al, 2011;Enss et al, 2024) or biotic interactions including competition for food and space (Lake et al, 2007).…”