DOI: 10.5061/dryad.2v6wwpzsz
title: Macroinvertebrate ecosystem engineering affects streambed retention of microplastics

description: Microplastic pollution of aquatic environments threatens human health,
 ecosystem processes, and biodiversity. Many existing models of
 microplastic movement in streams do not account for biotic effects on
 microplastic fate. Ecosystem engineering by net-spinning caddisflies
 (Hydropsychidae) has been shown to substantially affect sediment and
 organic matter transport as well as streambed hydrology. Caddisfly
 engineering may likewise affect the movement of microplastic pollution in
 streams. We used a controlled 11-d flume experiment to investigate the
 potential for caddisflies to serve as a biotic control on microplastic
 transport. Flumes containing a single gravel dune were randomly assigned
 to density treatments: control (0 caddisflies/m2) or stocked with 500,
 800, or 2500 caddisflies/m2, incubated (d 1–10) to allow for caddisfly
 silk structure construction, inoculated (d 11) with PVC microplastics (333
 µm–1 mm), and sampled (d 12). Microplastic was quantified as caught in a
 drift net (downstream transport), eaten by caddisflies (ingestion), or
 captured in caddisfly silk structures or settled into the gravel dune
 (i.e., total streambed retention). Mean downstream plastic transport was
 9% lower than the control in the 800 caddisflies/m2
 treatment and 10% lower in the 2500 caddisflies/m2
 treatment (p &lt; 0.001 and p = 0.003, respectively). Mean
 total streambed retention was 9% higher than control in the 800
 caddisflies/m2 treatment (p &lt; 0.001) and 910% higher in
 the 2500 caddisflies/m2 treatment (p = 0.004). Ingestion of
 plastic by caddisflies was rare and highly variable (0–0.55% of plastic
 particles) but did increase with caddisfly density (p = 0.002). This work
 represents one of the first investigations of animal ecosystem engineering
 as a control on the movement and fate of microplastic particles in fresh
 waters and establishes a foundation for future research on biotic control
 of microplastic transport. Our results suggest that ecosystem engineering
 by net-spinning caddisflies may serve as a biotic control of microplastic
 transport in freshwater streams. 
description: # Macroinvertebrate ecosystem engineering affects streambed retention of
 microplastics: *** The dataset contains counts of microplastic particles
 recovered from different locations within experimental flumes which were
 set up to test the effect of caddisfly population density on microplastic
 transport and fate. The used GLMMs to show that downstream transport of
 microplastics was reduced at the two highest stocked densities of
 caddisflies, which corresponded to an increase in microplastic stored in
 the streambed. Caddisflies also consumed a minimal amount of microplastic.
 ## Description of the Data and file structure The raw data is stored in
 the file "flumestats\_R.csv". Each row in the data represents
 measurements from a single trial in the experiment. The raw data includes
 the following variables: Flume\_Number : A numerical identifier for the
 experimental flume used for a given trial. Trial\_Number: A numerical
 identifier for the time block of a given trial. Stock\_Dense: The number
 of caddisflies per square meter stocked in the flume. Stock\_Number: The
 raw number of caddisflies stocked in the flume. Final\_Number: The number
 of live caddisflies recovered from the flume at the end of the experiment.
 Per\_Mort: The proportion of caddisflies which died before the conclusion
 of the trial. Caddis\_Biomass: The biomass of the dried bodies of
 caddisflies which were living at the end of the experiment, reported in
 grams. Silk\_Num: The number of microplastic particles recovered from
 caddisfly silk in the trial. Silk\_Per: The proportion of all recovered
 microplastic particles from the trial which were recovered from silk.
 Net\_Num: The number of microplastic particles recovered from the drift
 net in the trial. Net\_Per. The proportion of all recovered microplastic
 particles from the trial which were recovered from the drift net.
 Caddis\_Num: The number of microplastic particles recovered from caddisfly
 bodies in the trial. Caddis\_Per: The proportion of all recovered
 microplastic particles from the trial which were recovered from caddisfly
 bodies. Dune\_Num: The number of microplastic particles recovered from the
 gravel dune in the trial. Dune\_Per: The proportion of all recovered
 microplastic particles from the trial which were recovered from caddisfly
 bodies. Total\_Num: The total number of microplastic particles recovered
 from each trial. MP\_mg\_caddis: The number of microplastic particles
 recovered in caddisfly bodies per milligram of dry caddisfly tissue. The
 file named "Final Microplastic analysis.Rmd" contains the R code
 necessary to reproduce the analysis reported in the manuscript, as well as
 some code used for exploratory analysis and generation of figures for
 conference presentations. The analysis can be repeated by knitting the
 .Rmd file provided that the .csv file is stored in the same location.
 Running the code contained in the .Rmd will write additional .csv files
 used for making tables and several .tiff images containing figures to the
 working directory. ## Sharing/access Information The data can also be
 requested by contacting the lead author at
 samuel.fritz2@student.montana.edu Raw counts of microplastic particles
 were derived from images taken under a Leica D60 dissecting microscope.
 The original images may be obtained upon request.