DOI: 10.5061/dryad.0zpc8670z
title: Ecological data for: Subsidy accessibility drives asymmetric food web responses

description: Global change is fundamentally altering flows of natural and anthropogenic
 subsidies across space and time. After a pointed call for research on
 subsidies in the 1990s, an industry of empirical work has documented the
 ubiquitous role subsidies play in ecosystem structure, stability and
 function. Here, we argue that physical constraints (e.g., water
 temperature) and species traits can govern a species’ accessibility to
 resource subsidies, which has been largely overlooked in the subsidy
 literature. We examined the input of a high quality, point-source
 anthropogenic subsidy (aquaculture feed) into a recipient freshwater lake
 food web. By using a combined bio-tracer approach, we detect a gradient in
 accessibility of the anthropogenic subsidy within the surrounding food web
 driven by the thermal preferences of three constituent species,
 effectively rewiring the recipient lake food web. Since aquaculture is
 predicted to increase significantly in coming decades to support growing
 human populations, and global change is altering temperature regimes, then
 this form of food web alteration may be expected to occur frequently. We
 argue that subsidy accessibility is a key characteristic of recipient food
 web interactions that must be considered when trying to understand the
 impacts of subsidies on ecosystem stability and function under continued
 global change.
description: <strong>Biomass Distribution
 Data:</strong> The proportion of
 total biomass of each species sampled during the Ontario Ministry of
 Northern Development, Mines, Natural Resources and Forestry (MNDMNRF) 2017
 Broad-scale Monitoring program across five sites in Georgian Bay were
 extracted from the Upper Great Lakes Management Unit Lake Huron Report
 PS-LHA-2017-01 (MNDMNRF, 2018). Data was extracted from Figure 4, Figure
 7, Figure 10, Figure 12, and Figure 14 using WebPlot Digitizer. Data was
 normalized to 100 and summed for each thermal guild. 
 <strong>Fatty Acid Data:</strong>
 Muscle tissue samples were collected from fish and whole
 invertebrates for fatty acid (FA) analysis from both Parry Sound and
 control sites in the summer of 2016 and 2017. Fish samples were collected
 using Ontario multi-mesh gill nets following a modified broad-scale
 monitoring (BsM) protocol of the fish community (Sandstrom et al., 2013)
 and supplemented with targeted angling. Both overnight and daytime sets
 were employed in the sampling protocol. All gill nets were set for a
 duration of ~12 h before retrieving fish. Weight (g), length (mm), and two
 muscle tissue plugs from behind the dorsal fin were collected from fish.
 Snails and mussels (Unionidae sp., and Dreissena polymorpha) were
 collected from each sampling site to provide baseline stable isotope
 values. Additionally, feed and muscle tissue from farmed rainbow trout was
 also collected each year from Aqua-Cage Fisheries in Parry Sound. All
 samples were stored at -20˚C after collection until further analysis.
 Muscle tissues from a subset of the fish collected were sent for fatty
 acid analysis, along with feed and baseline samples. Frozen samples were
 delivered to Ryerson University – The Arts Lab (Toronto, ON, Canada) in
 2016, and both the Laboratory of Aquatic Sciences (Chicoutimi, QC, Canada)
 and Lipid Analytical Services (Guelph, ON, Canada) in 2017. All labs
 conducted fatty acid analysis using a combination of Bligh & Dyer
 and Morrison & Smith methods (Bligh & Dyer, 1959; Morrison
 & Smith, 1964). Individual FA weights (ug/g) were converted to a %
 FA composition and fatty acids with &gt;1% presence were retained for
 analysis. See Appendix S2: Section S2 of manuscript for details on
 statistical methods. <strong>Stable Isotope
 Data:</strong> A combination of data collected by
 the McCann Lab and the MNDMNRF were used. Note these methods pertain to
 samples collected by the McCann Lab in 2016 and 2017. Details on sample
 collection of additional Ontario Ministry of Northern Development, Mines,
 Natural Resources and Forestry (MNDMNRF) samples used in stable isotope
 analysis can be found in the Annual Report of Fisheries Assessment
 Projects Conducted on Lake Huron, 2017 (MNDMNRF, 2018).Muscle tissue
 samples were collected from fish and whole invertebrates for stable
 isotope (SI) analysis from both Parry Sound and control sites in the
 summer 2017. Fish samples were collected using Ontario multi-mesh gill
 nets following a modified broad-scale monitoring (BsM) protocol of the
 fish community (Sandstrom et al., 2013) and supplemented with targeted
 angling. Both overnight and daytime sets were employed in the sampling
 protocol. All gill nets were set for a duration of ~12 h before retrieving
 fish. Weight (g), length (mm), and two muscle tissue plugs from behind the
 dorsal fin were collected from fish. Snails and mussels (Unionidae sp.,
 and Dreissena polymorpha) were collected from each sampling site to
 provide baseline stable isotope values. Additionally, feed and muscle
 tissue from farmed rainbow trout was also collected each year from
 Aqua-Cage Fisheries in Parry Sound. All samples were stored at -20˚C after
 collection until further analysis. One muscle plug from all fish, feed,
 and baseline samples collected were prepared for stable isotope analysis.
 Samples were thawed in the lab and dried at 60 °C in a drying oven for 48
 h. Once dried, they were individually ground using a mortar and pestle and
 scooped into a labelled centrifuge tube. The samples were sent to the
 University of Windsor GLIER (Windsor, ON, Canada) laboratories for carbon
 and nitrogen isotopic analysis. See Appendix S2: Section S4 of manuscript
 for details on statistical methods.
 <strong>Hydroacoustic Data:</strong>
 In July 2017, both night-time and day-time hydroacoustic surveys
 were conducted in Lake Huron along four transects at increasing distances
 from the Aqua-Cage Fisheries cage-culture (Parry Sound, Ontario, Canada;
 Fig. 6). The central (C), transect started closest to the net-pen and was
 considered the experimental transect with the strongest predicted
 influence of net-pen, the west (W), east (E), and far eastern (EE)
 transects were considered reference transects. The C, W and E transects
 had a maximum depth of 111m, the EE transect had a maximum depth of 91m. 
 The day-time surveys were conducted from 2:30pm to 7pm, while the
 night-time surveys were conducted from 11:45pm to 4 am. The thermocline
 was estimated based on temperature profiles, sitting at approximately 10m
 below the surface.  All transects started well below the thermocline (all
 start depths &gt;40m). Hydroacoustic procedures were based on
 Parker-Stetter et al.’s (2009) “Standard operating procedures for
 fisheries acoustic surveys in the great lakes”. See Appendix S2: Section
 S3 of manuscript for full explanation of hydro acoustic survey and data
 post-processing.