DOI: 10.5061/dryad.1jwstqk3z
title: Ecological performance of native and invasive benthic freshwater fishes under elevated temperature

description: Climate warming of freshwater ecosystems is altering the performance and
 trophic interactions of native and non-native species. We compared the
 feeding efficiency and thermal tolerance of the Eurasian round goby
 (Neogobius melanostomus) and a trophically analogous native species,
 logperch (Percina caprodes), under current and projected mean summer
 surface temperatures for the nearshore lower Great Lakes (18°C and 25°C,
 respectively). At both temperatures, we quantified the functional response
 ratio (FRR) of these fishes—the ratio of their attack rate and prey
 handling time, which can predict trophic impacts in the field. At 18°C,
 juvenile logperch had a higher FRR than juvenile round gobies; however,
 adult round gobies had a higher FRR than logperch at either temperature,
 indicating a greater potential for trophic impacts. At 25°C, adult round
 gobies and logperch increased their prey consumption and FRR. Following
 acclimation to 18°C and 25°C, juvenile logperch exhibited a greater
 thermal acclimation capacity than the round goby. These results underscore
 the need for risk assessment to account for varied responses by native and
 non-native species to shifting thermal contexts.
description: <strong>Quantifying Habitat
 Temperatures</strong> Water temperature data for
 the upper St. Lawrence River were obtained from Melocheville, Quebec
 (45.319° N, 73.927° W), and Maitland, Ontario (44.635° N, 75.613° W),  and
 used as approximations for collection sites at Beauharnois and Morrisburg,
 respectively. Data from Melocheville was obtained in the summer of 2020
 from Reid and Ricciardi (2022) using a temperature logger that recorded
 water temperatures once per hour. Water temperature data from Maitland was
 retrieved during the summer of 2022 from the St. Lawrence River Institute
 using a temperature logger that recorded water temperatures at 15-minute
 intervals. For each location, mean daily temperatures were calculated for
 each 24-hour period from 16 July to 30 September 2022. The mean daily
 temperatures of Melocheville and Maitland were 22.3±0.30°C (17.2–34.0°C,
 min-max) and 22.6±0.23°C (16.0–27.3°C, min-max), respectively (Fig. 2).
 The number of days ≥25°C were 6 for Melocheville and 2 for
 Maitland. <strong>Comparative Functional
 Responses</strong> We examined the comparative FR
 of juvenile logperch and both adult and juvenile round gobies at two
 acclimation temperatures, 18°C and 25°C, which were selected to represent
 mean maximum nearshore surface water temperatures at present and in the
 latter half of this century, respectively, for nearshore lakes Erie and
 Ontario (Trumpickas et al., 2009, 2015). Both species and life stages were
 provided with a 2-week temperature acclimation before FR trials began,
 with the exception of logperch acclimated to 18°C. Logperch were provided
 with an additional 14 days of acclimation at 18°C to stabilize water
 quality (Yao et al., 2020; Saeed et al., 2022). At the start of FR trials,
 individuals were isolated in a 10-gallon aquarium (50 × 19 × 25 cm) and
 left to acclimate for a 24-hour period, during which they were starved to
 standardize hunger levels (Mofu et al., 2019a; Reid & Ricciardi,
 2022). The sides of aquaria were covered with an opaque barrier to prevent
 external visual stimuli from affecting prey consumption (Murray et al.,
 2013). Each experimental aquarium was maintained at the corresponding
 acclimation temperature (± 0.5°C). Aquaria also contained an air stone for
 oxygenation and a shelter (PVC pipe) as refuge to reduce stress.
 Prey items used in the FR trials were chironomid
 (<em>Chironomus </em>sp.) larvae, which are typically found in
 habitats occupied by logperch and round gobies and are a common component
 of their diets (French & Jude, 2001; Kornis et al., 2012). Hikari
 chironomid larvae (previously frozen and subsequently thawed for
 experiments) were distributed in seven densities (n=2, 4, 8, 16, 32, 64,
 and 140 larvae for logperch and juvenile round gobies; n=2, 4, 8, 16, 32,
 64, 180 larvae for adult round gobies) with four replicates per density.
 Within each series of 18ºC and 25 ºC temperature experiments, following
 the 24-hour trial acclimation period, each individual fish was used in one
 feeding trial (i.e., at one prey density assigned at random) and allowed
 to feed for three hours (Mofu et al., 2019a; Mofu et al., 2019b). The use
 of lower prey densities enables us to distinguish between Type II and Type
 III functional responses (Juliano, 2001). At the end of each FR trial,
 individuals were removed from their experimental tank, weighed, and
 measured for total length. The remaining chironomid larvae were collected
 and counted to identify the number of prey eaten (Mofu et al., 2019a).
 Control trials without fish were conducted at each prey density to confirm
 that the observed depletion of prey from the experimental tanks was a
 direct result of predation. <strong>Critical
 Thermal Maximum</strong>
 CT<sub>max</sub> was measured in a 38-L aquarium (50
 × 19 × 25 cm) at acclimation temperatures of 18°C and 25°C. Individuals
 were acclimated to each temperature treatment for 4–6 weeks prior to
 trials. A total of 12 logperch and 12 juvenile round gobies were tested
 per acclimation temperature, while 10 adult round gobies were tested at
 18°C and 9 individuals were tested at 25°C (McDonnell & Chapman,
 2015; Reid & Ricciardi, 2022). Size-matching based on total length
 was conducted within all groups and between logperch and juvenile round
 gobies. The experimental aquarium was equipped with an aerator for
 oxygenation, and an isolating breeding box containing gravel and a PVC
 shelter to decrease stress and offer refugia. For logperch and juvenile
 round gobies, two individuals from the same rearing tank were placed in
 separate chambers of the breeding box (25 × 14 × 15 cm) divided using an
 opaque barrier. Adult round gobies were tested in their own individual
 breeding box (26 × 15 × 16 cm). Logperch used in CT<sub>max
 </sub>trials were the same individuals used for FR trials.
 CT<sub>max </sub>trials were conducted after completing FR
 experiments and each fish was given a minimum of seven days between
 experimental trials for recovery (Reid & Ricciardi, 2022). Fish
 were not reused among CT<sub>max </sub>experiments.
 Prior to the start of each trial, fish were starved for a 24-hr
 period (McDonnell & Chapman, 2015; Wells et al., 2016). The
 experimental aquarium was maintained at the corresponding acclimation
 temperature (± 0.5°C). Fish were placed in the breeding box and left to
 acclimate for two hours while the CT<sub>max</sub> apparatus
 circulated water so individuals could recover from handling stress and
 acclimate to trial conditions (Potts et al., 2021; Reid &
 Ricciardi, 2022). Water temperature within the experimental aquarium was
 controlled by a heating immersion circulator (Julabo
 CORIO<sup>TM</sup>, Seelbach, Germany). At the start of each
 trial, the water temperature was increased at a fixed rate of 0.3°C/min
 (Becker & Genoway, 1979) and monitored and recorded for the
 duration of each trial. Fish were exposed to increasing water temperature
 until they displayed a loss of equilibrium (Becker & Genoway,
 1979), at which point the end temperature (CT<sub>max</sub>)
 was recorded. Loss of equilibrium for round gobies was determined manually
 since this species lacks a swim bladder (Kornis & Vander Zanden,
 2010). When individuals began to show signs of increased breathing rates
 and reduced movement, a probe was used to gently turn the fish over
 (Matern, 2001). If fish were unable to re-orient themselves after five
 seconds, they were considered to have lost equilibrium (Carline &
 Machung, 2001). Immediately following loss of equilibrium, fish were
 transferred into a recovery aquarium, containing an aerator, and
 monitored. Once recovered, the total length and weight were recorded, and
 any mortality was noted. A time-stamped webcam
 monitored fish behaviour during trials to reduce disturbance. The footage
 was reviewed to confirm the onset of behavioural thresholds;
 CT<sub>max</sub> and agitation temperature
 (T<sub>ag</sub>). T<sub>ag</sub> was identified as
 the temperature at which a fish swims agitatedly around the breeding box
 for a period longer than 40 seconds, indicating the onset of avoidance
 behaviour before CT<sub>max </sub>is reached (McDonnell
 & Chapman, 2015; Potts et al., 2021). This avoidance behaviour is
 indicative of the threshold at which fish seek out a cooler environment
 (McDonnell & Chapman, 2015; Wells et al., 2016). Additional
 metrics were derived using CT<sub>max </sub>and
 T<sub>ag</sub> values and compared between acclimation
 treatments. First, the thermal agitation window
 (T<sub>aw</sub>) was calculated by subtracting Tag from CTmax
 (Wells et al., 2016). The acclimation agitation window
 (A<sub>aw</sub>) was calculated by subtracting the acclimation
 temperature from T<sub>ag </sub>(McDonnell et al., 2021). The
 modified thermal safety margin (TSM) was calculated by subtracting the
 acclimation temperature from CT<sub>max</sub> (McArley et al.,
 2017; McDonnell et al., 2021). Lastly, the acclimation response ratio
 (ARR), a metric for quantifying thermal plasticity, was calculated as the
 change in CT<sub>max</sub> per degree change in the
 acclimation temperature (T<sub>acc</sub>) for both acclimation
 treatments (Claussen, 1977).
description: # Ecological performance of native and invasive benthic freshwater fishes
 under elevated temperature
 [https://doi.org/10.5061/dryad.1jwstqk3z](https://doi.org/10.5061/dryad.1jwstqk3z) ## Description of the data and file structure Three files are provided: 1) an Excel spreadsheet containing raw data from field temperature loggers, functional response (FR) experiments, and thermal tolerance (CTmax) experiments; 2) a Word file with the R-script used to analyze the data; and 3) supplementary tables & figure. ## Variables - Functional response (FR) data HT = holding tank EX = experimental tank Length = total length of fish (mm) Weight = live mass of fish (g) Trial temp = temperature during the trial (Celsius) Density = food (prey) density (#) Left = unconsumed food (#) Eaten = consumed food (#) Treatment = temperature (18C or 25C) Prop= proportion of food consumed Tacc = Acclimation temperature LS = life stage Sp = fish species ## **Variables - Critical Thermal Maximum (CTmax) data** TAGW = thermal agitation window TAGTemp = agitation temperature AAW = acclimation agitation window TSM = thermal safety margin Length = total length of fish (mm) Weight = live mass of fish (g) BB = Breeding box (divided into two sections, Left and Right) in which the treatment was applied. Acc Time = acclimation time HT = holding tank Sp = species LS = life stage NA = Not available ## Temperature logger data Date = date of data collection at either of two sites (Melocheville, or Maitland) on the St Lawrence River. Temperature data (Celsius) for each of the two sites is listed for each date. ## Code R-code for functional response data analyses