Network-Based Biomonitoring: Exploring Freshwater Food Webs With Stable Isotope Analysis and DNA Metabarcoding

Zacchaeus G Compson,Michael T G Wright,Mehrdad Hajibabaei,Mohammad Sadnan Al Manir,R Allen Curry,Wendy A Monk,Teresita M Porter,Brian Hayden,Donald J Baird,Christopher J O Baker,Zoë O'Malley,Alex Bush

doi:10.3389/fevo.2019.00395

Abstract

Threatened freshwater ecosystems urgently require improved tools for effective management. Food web analysis is currently under-utilized, yet can be used to generate metrics to support biomonitoring assessments by measuring the stability and robustness of ecosystems. Using a previously developed analysis pipeline, we combined taxonomic outputs from DNA metabarcoding with a text-mining routine to extract trait information directly from the literature. This pipeline allowed us to generate heuristic food webs for sites within the lower Saint John/Wolastoq River and the Grand Lake Meadows (hereafter called the “GLM complex”), Atlantic Canada's largest freshwater wetland. While these food webs are derived from empirical traits and their structure has been shown to discriminate sites both spatially and temporally, the accuracy of their properties have not been assessed against other methods of trophic analysis. We explored two approaches to validate the utility of heuristic food webs. First, we qualitatively compared how well-trophic position derived from heuristic food webs recovered spatial and temporal differences across the GLM complex in comparison to traditional stable isotope approaches. Second, we explored how the trophic position of invertebrates, derived from heuristic food webs, predicted trophic position measured from δ 15N values. In general, both heuristic food webs and stable isotopes were able to detect seasonal changes in maximum trophic position in the GLM complex. Samples from the entire GLM complex demonstrated that prey-averaged trophic position measured from heuristic food webs strongly predicted trophic position inferred from stable isotopes (R 2 = 0.60), and even stronger relationships were observed for some individual models (R 2 = 0.78 for best model). Beyond their areas of congruence, heuristic food web and stable isotope analyses also appear to complement one another, suggesting a surprising degree of independence between community trophic niche width (assessed from stable isotopes) and food web size and complexity (assessed from heuristic food webs). Collectively, these analyses indicate that trait-based networks have properties that correspond to those of actual food webs, supporting the routine adoption of food web metrics for ecosystem biomonitoring.

Highlights

Freshwater ecosystems, which house a disproportionate amount of Earth’s biodiversity (Dudgeon et al, 2006), face multiple threats (Cazzolla Gatti, 2016; Hu et al, 2017)
Heuristic food webs constructed from DNA and paired trait information elucidated both spatial and temporal patterns in the Grand Lake Meadows (GLM) complex
Metawebs from the wetland region of the complex were relatively larger, denser, and had a higher maximum trophic position than metawebs from the transition and mainstem regions of the complex; metawebs from the transition region were generally the smallest and sparsest, with lower numbers of nodes, links, and maximum trophic positions compared to metawebs of the other regions (Figure 2)

Summary

Introduction

Freshwater ecosystems, which house a disproportionate amount of Earth’s biodiversity (Dudgeon et al, 2006), face multiple threats (Cazzolla Gatti, 2016; Hu et al, 2017). The very structural and ecological complexity that gives freshwater systems their capacity for biodiversity and ecosystem services makes them very difficult to study. This is true for the planet’s wetlands, which are generally viewed as hard to define, seasonally variable, and often inaccessible. Food web networks explicitly show biodiversity, species interactions, and structural and functional relationships of ecosystems (Dunne et al, 2002b; Thompson et al, 2012), and are an intuitive communication tool for environmental managers, when presenting to lay audiences. Constructing food webs is laborious (Thompson et al, 2012), underscoring the need for new tools that can facilitate this process to support wider implementation in bioassessment (Bohan et al, 2017)

Methods

Results

Conclusion